Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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potential to the first variety (IR 8) but have a better

resistance or tolerance to biotic and abiotic stresses.

‘Super’ rice being bred has fewer tillers but with all of

them productive (bearing panicle).

0003 Only about 4–5% of the world’s rice production

enters the international trade. The major exporters in

1997 were Thailand, Vietnam, India, the USA, and

Pakistan. The major importers in 1997 were Iran,

Brazil, Nigeria, the Philippines, Iraq, Saudi Arabia,

Malaysia, South Africa, and Co

te d’ Ivoire.

Morphology and Anatomy of the Spikelet

or Grain

0004 The rice grain (rough rice or paddy) consists of an

outer protective covering, the hull (husk), and the

edible rice caryopsis or fruit (brown, cargo, dehulled,

or dehusked rice) (Figure 1). Brown rice consists of

the outer layers of pericarp, seed coat, nucellus, and

germ or embryo, which are the maternal tissues, and

the endosperm. The endosperm consists of the aleur-

one layer and the starchy or inner endosperm. Pig-

ment is confined to the pericarp, but there is a varietal

difference in the extent of retention of pigment with

the degree of milling. The aleurone layer encloses the

embryo.

0005 The inedible hull constitutes 16–28% (mean 20%)

of rough rice weight. Brown rice consists of 1–2%

pericarp, 4–6% aleurone plus nucellus and seed coat,

1% embryo, 2% scutellum and 90–91% endosperm.

The aleurone and embryo cells are rich in lipid bodies

(spherosomes, 0.2–1.5 mm) and in protein bodies

(aleurone grains) containing inclusions of phytic acd

bodies or globoids (1–3 mm).

0006The endosperm cells are thin-walled and packed

with amyloplasts containing polyhedral compound

starch granules about 3–9 mm in size. Protein occurs

mainly in the form of large (1–2 mm) and small (0.5–

0.8 mm) spherical protein bodies and crystalline pro-

tein bodies (2–4 mm). Spherical protein bodies (PB I)

are rich in prolamin (alcohol-soluble protein), and

crystalline protein bodies (PB II) are rich in glutelin

(alkali-soluble protein). Spherosomes are present in

the subaleurone or the two outermost cell layers of

the endosperm.

Chemical and Nutritional Composition

0007Rice has one of the lowest protein contents (7%)

among the cereals. The bran layers and embryo are

richer in nonstarch constituents than the milled rice

(Table 1). The major nutritional advantage of brown

rice over milled rice is its higher content of B vitamins.

Although higher in minerals, bran phytic acid and

probably dietary fiber in the aleurone form com-

plexes with minerals and proteins, reducing their

bioavailability. The energy content of brown rice

and bran is higher than that in milled rice, owing

to the higher fat content. Rice has no vitamin A,

C, or D.

Awn

Lemma

Palea

Hull

Pericarp

Seed coat

Nucellus

Aleurone layer

Scutellum

Epiblast

Plumule

Embryo

Radicle

Rachilla

Inner

endosperm

Starchy

endosperm

Sterile lemmae

Dorsal

Ventral

Subaleurone

layer

fig0001 Figure 1 Longitudinal section of the rice grain. From Juliano BO (1984) In: Whistler RL, BeMiller JN and Paschall EF (eds) Starch

Chemistry and Technology, 2nd edn, p. 509. Orlando, FL: Academic Press, with permission.

4996 RICE

0008Although cereal proteins are deficient in lysine, rice

protein has one of the highest lysine contents among

them, corresponding to an amino acid score of 59%

in milled rice based on the Food and Agriculture

Organization/World Health Organization/United

Nations University (FAO/WHO/UNU) amino acid

pattern of 5.8% lysine as 100% (Table 2). The solu-

bility fractions of protein are about 15% of albumin–

globulin (water- and salt-soluble), 20% prolamin

(PB I) and 65% glutelin (PB II) in milled rice. Bran

proteins are 66–98% albumins. Prolamin is poor in

lysine but rich in sulfur amino acids. The high lysine

content of rice protein is due to the low prolamin

content.

0009The energy digestibility is higher in milled rice than

in brown rice owing to the lower dietary fiber and

phytic acid levels, as verified by the poor energy

digestibility of rice bran (Table 2). The true digestibil-

ity (TD) of milled rice protein is also higher than that

of brown rice, but the biological value (BV) is lower,

resulting in a similar net protein utilization (NPU).

Bran protein has a lower TD but a higher BV than

brown and milled rice proteins. The amino acid score

corrected for TD in rats proposed by the FAO as a

protein quality index shows similar values to NPU for

the rice proteins. Black or purple rice has a lower

brown rice NPU (72%) and higher tannin level

(0.6%) than red (NPU 83% and 0.2% tannin) and

nonpigmented rices (NPU 97% and  0.02% tannin),

but their milled rices have identical NPUs. Rice

tbl00 01 Table 1 Comparisonofnutrientcompositionofbrownrice,

milledriceandricebran

PropertyAmountsper100g

BrownriceMilledriceRicebran

Moisture(g)14.014.014.0

Energycontent(KJ)1520–16101460–15601670–1990

Energycontent(kcal)363–385349–373399–476

Crudeprotein(g)7.1–8.36.3–7.111.3–14.9

Crudefat(g)1.6–2.80.3–0.515.0–19.7

Crudefiber(g)0.6–1.00.2–0.57.0–11.4

Crudeash(g)1.0–1.50.3–0.86.6–9.9

Availablecarbohydrates(g)73–8777–8934–62

Totaldietaryfiber(g)2.9–4.00.7–2.317–29

Water-insolublefiber(g)2.00.515–27

Sugars(g)1.90.2–0.56.4

Thiamin(mg)0.3–0.60.02–0.111.2–2.5

Riboflavin(mg)0.04–0.140.02–0.060.18–0.43

Niacin(mg)3.5–5.31.3–2.426.7–49.9

Pantothenicacid(mg)1.41.06.8

VitaminB

(mg)0.50.23.7

Folate(mg)19858

VitaminE, a-tocopherol

(mg)

0.8–2.5<0.01–0.303–15

Calcium (m g)10–5010–3030–120

Phosphorus(g)0.17–0.430.08–0.151.1–2.5

PhyticacidP(g)0.13–0.270.02–0.070.9–2.2

Iron(mg)0.2–5.20.2–2.88.6–43.0

Zinc(mg)0.6–2.80.6–2.34.3–25.8

From JulianoBO(ed.)(1985)Rice:ChemistryandTechnology.St.Paul,MN:

AmericanAssociationofCerealChemists;UnitedStatesDepartmentof

Agriculture(USDA)(1998)NutrientDatabaseforStandardReference,

Release12.Riverdale,MD:NutrientDataLaboratory,USDABeltsville

HumanNutritionResearchCenter(availableathttp://www.nal.usda.gov/

fnic/foodcomp/).

tbl00 02 Table 2 Essentialaminoacidprofileandenergyandnitrogenbalanceingrowingratsofrawbrownrice,milledriceandricebran

PropertyBrownriceMilledriceRicebran

Arginine(gper16gN)7.17.97.6

Histidine(gper16gN)2.42.22.5

Isoleucine(gper16gN)4.04.14.0

Leucine(gper16gN)7.97.97.3

Lysine(gper16gN)3.63.44.6

Methionine(gper16gN)2.22.22.2

Methionineþcystine(gper16gN)3.34.24.4

Phenylalanine(gper16gN)4.95.14.5

Phenylalanineþtyrosine(gper16gN)8.58.37.5

Threonine(gper16gN)3.53.44.0

Tryptophan(gper16gN)1.21.10.8

Valine(gper16gN)5.65.86.3

Aminoacidscore

(%)635980

Digestibleenergy

(percentageoftotal)94.3b96.6a67.4c

Truedigestibility(TD)

(percentageofdietN)96.9b98.4a78.8c

Biologicalvalue

(percentageofdigestedN)68.9b67.5b86.6a

Netproteinutilization

(percentageofdietN)66.7b66.4b68.3a

AminoacidscoreTD(%)615863

Basedon5.8goflysineper16gofNas100%.

Ineachline,meanvaluesfollowedbythesameletterarenotsignificantlydifferentatthe5%level(byDuncan’smultiplerangetest).

From Eggum BO,JulianoBO,andManin

gatCC(1982)Proteinandenergyutilizationofricemillingfractionsbyrats.QualitasPlantarumPlantFoodsfor

HumanNutrition31:371–376.

UnitedStatesDepartmentofAgriculture(USDA)(1998)NutrientDatabaseforStandardReference,Release12.Riverdale,MD:NutrientDataLaboratory,

USDA.BeltsvilleHumanNutritionResearchCenter(availableathttp://www.nal.usda.gov/fnic/goodcomp/).

RICE 4997

complements legumes in amino acid composition for

human diets.

0010 Cooking and parboiling reduces the TD in growing

rats by 5–15%, with a corresponding increase in BV

but little change in NPU. However, lysine digestibility

remains close to 100%, and cystine digestibility drops

to about 82%. The fraction that remains in the feces

as fecal protein particles represents the lipid-rich core

of large PB I, with less than 1% lysine in its protein

but is rich in cystine. PB II is readily digested.

0011 Starch varies in apparent amylose content (as de-

termined by iodine colorimetry): waxy, 1–2%; very

low amylose, 2–10%; low, 10–20%; intermediate,

20–25%; and high, 25–33%, all on a milled rice dry-

weight basis. The glycemic index of cooked brown

rice tends to be lower than that of cooked milled rice

owing to the higher amounts of phytic acid and

fiber in brown rice. Among cooked milled rices, the

glycemic index decreases with increasing amylose

content regardless of the cooking method (Table 3).

Processing, including parboiling, tends to reduce the

glycemic index. Resistant starch is 5% and may

not be as discriminating as the glycemic index in

humans.

0012Breeding efforts to improve the nutritional value of

rice grain include: a higher micronutrient density,

(higher iron, zinc, and vitamin A), low phytic acid

(high phosphate) content, low prolamin content

absence of lipoxygenase-3 activity and allergenic

globulin, and transgenic rice endosperm with vitamin

A, with the soybean glycinin gene, and with the

soybean ferritin gene.

Grading, Handling, and Storage

0013There is no international standard for milled rice

size and shape. The International Rice Research

Institute (IRRI) uses the following scale for size:

extra long, > 7.50 mm; long, 6.61–7.50 mm; medium,

5.51–6.60 mm; and short, < 5.50 mm. For grain shape

based on the length:width ratio, the following scale is

used: slender, > 3.0; medium, 2.1–3.0; bold, 1.1–2.0;

and round, 1.0. Grades are based on grain size

and shape, degree of milling, percentage head or

tbl0003 Table 3 Comparison of glycemic index and in vivo resistant starch of various rice and rice products

Ricefood

Amylose content

(%) Glycemic index

In-vivo resistant

starch (%)

Percentage of glucose Percentage ofbread (no.)

Brown rice

Waxy purple 0–2 78 + 8 112 + 11 (1)

Low amylose 15–20 81 + 7 116 + 10 (3)

Intermediate amylose 20–25 55 + 579+ 6 (3)

High amylose 25–33 66 + 794+ 10 (1)

Milled rice

Waxy/low amylose 0–2/15–20 88 + 3 126 + 4 (3)

Long grain 20–33 56 + 281+ 3 (13) 3.9

Intermediate/high amylose 20–33 59 + 383+ 5 (3)

Instant rice 15–25 91 + 4 128 + 4 (2) 5.1

Milled parboiled rice

Low/intermediate/high amylose 15–33 47 + 368+ 4 (13) 3.6 + 0.9

Specialty rices 20–25 54 + 178+ 1 (4)

Rice pasta, brown 15–20 92 + 8 131 + 11 (1)

Rice noodles (Chinese) 25–33 58 + 483+ 5 (1)

Rice noodles (Thai) 25–33 54 + 577+ 7 (2)

Brown-rice cakes, molded 15–20 86 + 9 123 + 6 (2)

Brown-rice cakes, molded 25–33 61 + 587+ 7 (1)

Puffed rice 15–20 86 + 7 123 + 11 (3)

Rice Bubbles 15–20 88 + 7 126 + 10 (2)

Rice Krispies 15–20 82 + 4 117 + 5 (1)

Rice Chex cereal 15–20 89 + 4 127 + 5 (1) 2.9

Rice bran 15–20 19 + 327+ 4 (1)

White bread with 20% rice bran 25–33 55 + 879+ 12 (1)

Apparent amylose content: waxy 1–2%, low 15–20%, intermediate 20–25%, and high 25–33%.

Mean + standard deviation. Based on blood plasma glucose value for the glucose diet as 100%, and that for the white bread diet as 100%, respectively

(GI of glucose is 0.70 of the GI of white bread). Number of reports in parentheses.

From Food and Agriculture Organization (1998) Carbohydrates in Human Nutrition. Rome: FAO; Foster-Powell K and Brand Miller J (1995) International

Tables of Glycemic Index. American Journal of Clinical Nutrition 62: 869S–893S; Panlasigui LN (1989) Glycemic Response to Rice, Ph.D. dissertation,

University of Toronto; Jenkins DJA, Cuff D, Wolever TMS et al. (1987) Digestibility of carbohydrate foods in an ileostomate: relationship to dietary fiber, in

vitro digestibility, and glycemic index. American Journal of Gastroenterology 82: 709–717.

4998 RICE

whole-grain milled rice, immature grains, damaged

(discolored) and heat-damaged grains (chalky grains,

red grains and red-streaked grains), aroma, and

organic and inorganic extraneous matter.

0014 An important property of harvested grain is its

moisture content: 14% on a wet-weight basis is

considered a safe storage value; grains become

susceptible to fissuring from moisture adsorption

stress below critical moisture contents of 12–16%,

depending on the variety. Aging of sun-/oven-dried

rough rice for up to 2 months after harvest at ambient

temperature < 15



C improves milling yields and

makes milled rice expand more during cooking and

become more flaky. Heating during grain drying

accelerates aging.

Processing and Food Uses

0015 The per-capita consumption of milled rice is 86 kg per

year in 1999 in Asia as compared with 4–31 kg in

other continents. It is consumed mainly as milled rice.

About 20% of rice is consumed as parboiled rice.

Parboiling consists of boiling or steaming steeped

rough rice until the hull starts to open, and then

cooling and drying the gelatinized grain. Diffusion

of bran B vitamins into the endosperm occurs during

parboiling. Mycotoxins are a potential problem in

parboiled rice. Milling involves dehulling, followed

by removal of the outer 7–10% of the brown rice,

either by friction or by abrasion, removing most of

the pericarp, seed coat, nucellus, aleurone layer, and

the germ. In the Engelberg mills, hull and bran are

removed together in one step with high grain break-

age. Milling is done in several steps in modern cone

mills with tempering in between to minimize break-

age. Many modern mills have shifted to milling

at > 14% moisture to minimize grain breakage and

to moisture mist treatment (through hollow shaft)

during milling to soften the bran and improve surface

gloss.

0016 There are various ways of cooking milled rices. In

tropical Asia, they are prewashed to remove dirt, but

this results in losses of B vitamins and fat. Presoaking

for 30 min reduces cooking time (particularly of par-

boiled rice). Grain cracking during soaking is minim-

ized by adjusting milled rice moisture content to 15%

by high-pressure hydration to minimize cracking.

Rice may be cooked in the amount of water that it

will absorb, or boiled in excess water and the cooking

liquor discarded. A steaming step is used in Indonesia

and also for waxy rices. Oil or ghee may be added in

the Middle East, and this reduces surface stickiness.

Enriched rice premixes containing iron and B vita-

mins resistant to washing have been developed for

rice, but have not been popular because of additional

expense; the enriched rice can be readily distinguished

from ordinary grain.

0017Apparent amylose content (AC) correlates posi-

tively with water absorption and volume expansion

during cooking, and with the hardness of boiled rice.

South Asian consumers prefer high-AC intermediate-

gelatinization temperature (GT > 70



C) rice, South-

east Asians prefer intermediate-AC, intermediate-

GT rice. Japonica rices preferred in Japan, Korea,

Taiwan, and northern China are mainly low-AC,

low-GT (70



C), with some having an intermediate

AC in Europe. Only in Laos and north and north-east

Thailand is steamed waxy rice consumed as a staple.

The amylopectin of low-GT, high-AC rice has a

longer mean chain length than the amylopectin of

intermediate-GT, high-AC rice. Among waxy and

low-AC rices, low-GT rice is a softer cooked rice

than high-GT rice, but among intermediate- and

high-AC rices, intermediate GT rice is a softer cooked

rice than low-GT rice. Longer-chain amylopectin con-

tributes to the flaky cooked rice of low-GT, high-AC

rices. Amylopectin staling is lower in low-GT cooked

rice than in higher-GT rice within each amylose type

and is reversed by heating.

0018Specialty rices include Italian Arborio rice for

making risotto, waxy rice (sweet rice with an

opaque grain), Thai Jasmine rice (aromatic low-

AC long grain) and Punjab Basmati (aromatic

intermediate AC long grain that elongates when pre-

soaked rice is cooked). 2-Acetyl-1-pyrroline was

the first major aroma principle identified in raw

and cooked aromatic rices, and others are being

characterized.

0019Various rice products are prepared for which

specific AC types are preferred (Table 4). Freshly

and well-milled rice is preferred for rice products to

prolong shelf-life by minimizing fat rancidity in the

stored products. Parboiled rices are preferably high

and intermediate AC, whereas extruded and flat

noodles use mainly aged, high-AC, low-GT rices.

Rice with a low-starch GT is preferred in rice pud-

dings, breads and cakes, and beer adjuncts. Waxy and

low-AC rices are preferred for rice wines (for a higher

ethanol yield) and in frozen sauces, desserts, snacks,

and sweets, because of their slow staling rate. Rice

crackers are prepared from waxy and nonwaxy rices.

Parboiled rice is preferred over raw rice for idli (pud-

ding) and dosai (cake) with rice:black gram usually

fermented at a 3:1 weight ratio. The thermophysical

properties of starch such as the glass transition tem-

perature, gelatinization temperature, enthalpy of

raw starch, staled amylopectin melting (45–60



C),

amylose–lipid complex I (< 100



C) and II (>100



melting, and staled amylose melting (> 130



of gelatinized starch affect the properties of rice

RICE 4999

products in addition to the amylose–amylopectin

ratio and protein content.

0020 The use of rice bran in cereal products has in-

creased in recent years owing to the hypocholestero-

lemic effect, in humans, of the factor(s) in the high (up

to 4.4%) unsaponifiable fraction of its oil, such as

t-oryzanol (cycloartenol, 24-methylene-cycloartanol

and campestrol esters of ferulic acid), tocopherols

and tocotrienols, an analog of tocopherol (vitamin

E). Defatted bran has no hypocholesterolemic activ-

ity, unlike in oats, where the active principle is soluble

b-glucan. Inactivation of antinutrition factors – tryp-

sin inhibitor, oryzacystatin, and hemaglutinin-lectin –

and lipase and lipoxygenase that are concentrated in

the rice bran by heat treatment and extrusion cooking

improves the shelf-life of the bran and its nutritional

value to poultry. By contrast, the antinutrition factor

phytic acid is heat-stable. Phytic acid in rice bran and

brown rice has been recently reported to have some

medicinal activity in preventing some types of cancer.

Phytic acid content of rice bran is highest among

cereal brans (3–8% phytic acid, Table 1).

0021 The total rice bran oil production in 1986–1988

was 600 000 tonnes per year, mainly in India, China,

Japan, and Vietnam, according to FAO. This

represented only 13% of potential bran oil produc-

tion, requiring immediate oil extraction or stabiliza-

tion because of bran lipase. The high hull

contamination (70%) of rice bran produced by Eng-

leberg mills makes oil extraction from their ‘bran’

uneconomical. Essential fatty acid content of rice oil

is 34.2% 18:2 and 1.5% 18:3. Levels of oryzanol,

tocopherols, and tocotrienols and unsaponifiable

matter differ among crude oils, and oryzanol, toco-

pherols, and tocotienols may be reduced by up to

90% by conventional refining and deodorizing.

See also: Amino Acids: Properties and Occurrence;

Starch: Resistant Starch

Further Reading

Chikubu S, Ishitani T and Ohtsubo K (eds) (1996) Science

of Rice (in Japanese). Tokyo: Asakura Publishing

Company.

De Datta SK (1981) Principles and Practices of Rice Pro-

duction. New York: John Wiley.

Food and Agriculture Organization (FAO) (1985) Rice

Processing Industries. Proceedings of the FAO/UNDP

Regional Workshop, Jakarta, 15–20 July 1985. Bang-

kok: FAO Regional Office for Asia and the Pacific.

tbl0004 Table 4 Apparent amylose content (AC) type and other properties reported as preferred for various processed rice products

Rice-based product AC type Other properties

Wx Low Int. High

Parboiled rice þ þ þþ þþ

Precooked/quick cooking þþ þþ Based on table rice AC

Expanded rice þþþþ AC not a major factor

Expanded rice, molded þþþþWaxy does not expand

Rice cereals/snacks þþþLow fat, texture affected by AC

Extruded rice food þþþLow fat

Rice-based infant food þþ Low fat

Rice flour and starch þþþþ Wet milling process, freshly milled rice

Rice crackers/biscuits þþ þþ þ þ Japanese arare, senbei

Rice puddings þþ Japanese uiro

Rice breads þþþLow GT

Unleavened rice bread þþ Pakistani roti

Rice cakes, steamed þþþ Fermented/nonfermented

Rice cakes, baked þþþþ Celiac disease, low GT

Flat noodles/rice paper þþþþLow shear process

Extruded rice noodles þþþHard gel consistency

Rice pasta þþþRaw and parboiled rices

Rice frozen sauces þþ Gel stability

Rice desserts/sweets þþ Gel stability

Fermented rice foods þþþþParboiled idli, dosai

Rice wines þþþ Low protein, low fat

Beer adjunct þ Low GT, low fat

Rice in batters and fried foods þ þ þþ þ

Rice in thickeners þþ Gel stability

Wx, waxy; Int., intermediate; GT, gelatinization temperature.

Reported preferred AC type as raw material for rice products.

þþ preferred more often than þ.

Juliano BO (1998) Varietal impact on rice quality. Cereal Foods World 43: 207–211, 214–216, 218–222.

5000 RICE

Huke RE and Huke EH (1990) Rice Then and Now.

Manila: International Rice Research Institute.

International Rice Research Institute (IRRI) – Centro Inter-

national de Agricultura Tropical (CIAT) – West African

Rice Development Association (WARDA) (1997) Rice

Almanac, 2nd edn. Manila: IRRI; Cali, Colombia: CIAT;

Bouake

,Co

te d’Ivoire: WARDA.

Khush GS and Toenniessen GH (eds) (1991) Rice Biotech-

nology. Wallingford, UK: CAB International; Manila:

International Rice Research Institute.

Juliano BO (ed.) (1985) Rice: Chemistry and Technology,

2nd edn. St. Paul, MN: American Association of Cereal

Chemists.

Juliano BO (1993) Rice in Human Nutrition. Rome: Food

and Agriculture Organization; Manila: International

Rice Research Institute.

Juliano BO (1997) Rice Products in Asia. Bangkok: Food

and Agriculture Organization Regional Office for Asia

and the Pacific.

Juliano BO (1998) Varietal impact on rice quality. Cereal

Foods World 43: 207–211, 214–216, 218–222.

Juliano BO and Villareal CP (1993) Grain Quality Evalu-

ation of World Rices. Manila: International Rice Re-

search Institute.

Marshall WE and Wadsworth JI (eds) (1994) Rice Science

and Technology. New York: Marcel Dekker.

Satake T (1990) Modern Rice Milling Technology. Tokyo:

University of Tokyo Press.

Tsuno Foods and Rice (1998) First International Sympo-

sium on Disease Prevention by IP6 and Other Rice

Components, Kyoto, June 8–9, 1998, Abstracts.

Wakayama, Japan: Ito-gun.

United States Department of Agriculture (USDA) (1998)

Nutrient Database for Standard Reference, Release 12.

Riverdale, MD: Nutrient Data Laboratory, USDA Belts-

ville Human Nutrition Research Center (available at

http://www.nal.usda.gov/fnic/food comp/).

RICKETS AND OSTEOMALACIA

J J B Anderson and S U Toverud, University of North

Carolina, Chapel Hill, NC, USA

S C Garner, Duke University Medical Center, Durham,

NC, USA

Introduction

0001 The terms ‘rickets’ and ‘osteomalacia’ refer to condi-

tions in which mineralization is impaired, usually as a

result of nutritional deficiencies of vitamin D and/or

calcium. Although both conditions share common

physical and microscopic abnormalities, rickets,

which is only seen in infancy and childhood, has

more severe manifestations in deformities of bone

because of the greater plasticity of the young skeleton.

Even though deficiency of vitamin D is a frequent

cause of rickets and osteomalacia, vitamin D nutri-

ture of individuals and populations has not been well

investigated, in part because of the significant contri-

bution of sunlight exposure to the nutritional status

of vitamin D and in part because of the difficulty of

accurately assessing vitamin D intakes from foods

and beverages. Although rickets still remains a prob-

lem in much of the developing world, preventive

strategies have led to its virtual disappearance in the

developed world – with a few notable exceptions –

because of food fortification and supplementation of

this essential fat-soluble vitamin. Osteomalacia and

the less severe hypovitaminosis D, on the other

hand, appear to be increasingly more serious public

health problems in the developed nations. As longev-

ity continues to increase, the older segments of

populations in affluent nations are at risk of insuffi-

cient vitamin D.

Dietary Vitamin D Intakes in the USA

0002No national survey findings exist on vitamin D

intakes by populations. A few studies involving

small numbers of subjects have shown that intakes

by elderly women and shut-in females and males have

been consistently below recommended intakes; low

intakes have also been verified indirectly from meas-

urements of serum 25-hydroxyvitamin D concentra-

tions of subjects living at northern latitudes during

winter and spring months.

Vitamin D Recommendations

0003Recommended intakes, also known by the specific

term dietary reference intakes (DRIs) in the USA, of

vitamin D have been designated in 1997 as adequate

intakes (AIs), rather than recommended dietary

allowances (RDAs). In its recent reevaluation the

Food and Nutrition Board of the Institute of Medi-

cine did not think that sufficient data were available

to establish with scientific certainty new RDAs for

vitamin D. Table 1 lists the recently established AIs

for vitamin D. Intakes that meet these AIs should

RICKETS AND OSTEOMALACIA 5001

prevent rickets or osteomalacia. Lower intakes of

vitamin D by individuals who get adequate sunlight

on a daily basis should also be able to prevent these

diseases.

Primary Causes and Abnormalities

0004Human vitamin D deficiency, which may result from

inadequate dietary intake and/or skin biosynthesis

of vitamin D (Figure 1), is a primary cause of

rickets. The active hormonal form of vitamin D,

1,25-dihydroxy-vitamin D (1,25(OH)

D, also called

calcitriol, has an important role in intestinal absorp-

tion of calcium and phosphate, bone metabolism

and mineralization, and calcium homeostasis. Other

roles are not yet well understood and include con-

servation of calcium and phosphate by the kidney,

interaction of the hormone with the immune system,

skin and skeletal muscle, and enhanced differenti-

ation of cells. Rickets may also be caused by inad-

equate calcium intake alone, as in the case of children

living in Nigeria. It is characterized by several clinical

features and laboratory measurements of blood

(Table 2).

0005Rickets describes the disordered growth and min-

eralization of the growth plate of the long bones. The

resulting abnormalities, widening of the growth

plate, delayed conversion of the growth plate cartil-

age to bone, and irregularly arranged bone trabeculae,

tbl0001 Table 1 Recommended adequate intakes (AI) of vitamin D in

the USA

Life-stage group: age and gender AI (mg day

1

)

Infants 0–1 years 5

Children

1–3 years 5

4–8 years 5

Males

9–13 years 5

14–18 years 5

19–30 years 5

31–50 years 5

51–70 years 10

>70 years 15

Females

9–13 years 5

14–18 years 5

19–30 years 5

31–50 years 5

51–70 years 10

>70 years 15

Pregnancy

<18 years 5

19–30 years 5

31–50 years 5

Lactation

<18 years 5

19–30 years 5

31–50 years 5

1 mg ¼ 40 IU of vitamin D.

From Institute of Medicine, Food and Nutrition Board (1997) Dietary

Reference Intakes for Calcium, Phosphorus, Magnesium,Vitamin D, and

Fluoride. Washington, DC: National Academy Press, with permission.

Source

No vitamin D in diet

No sunlight

Fat malabsorption

Causes of

deficiency

Biotransformation

of vitamin D

Liver disease

Drug effects

Nephrectomy

Renal disease

Hypo-PTH

Genetic defect

in 1-hydroxylase

Genetic defects in receptor:

Poor hormone binding

Unstable receptor

Diet:

Vitamin D

25-hydroxylase

25(OH)D

1a-hydroxylase

Vitamin D

or D

Skin:

7-dehydrocholesterol

Intestinal

absorption

Intestine Liver

(+)

1,25(OH)

25(OH)D

Kidney Target organs

Bone

Small

intestine

Other

tissues

Hypocalcemia

Hypophosphatemia

PTH

fig0001 Figure 1 Causes of vitamin D deficiency. PTH, parathyroid hormone. Reproduced from Cholecalciferol and Ergocalciferol/Rickets

and Osteomalacia, Encyclopaedia of Human Nutrition, Sadler MJ, Strain JJ and Caballero B (eds), 1999, Academic Press.

5002 RICKETS AND OSTEOMALACIA

are only seen when the vitamin D deficiency occurs

during childhood or adolescence, i.e., before the

growth plates close.

0006 Osteomalacia describes abnormalities resulting

from delayed and reduced mineralization of mature

bone, whether trabecular or cortical. This mineral-

ization defect leads to a widened area of unminera-

lized bone matrix on the bone surface, called osteoid.

Osteomalacia is observed at all ages.

0007 Infants and young children suffer from growth re-

tardation primarily because of the stunted growth of

the long bones, and may become bow-legged because

of the reduced mechanical strength of these bones.

Skeletal muscle weakness and increased urinary

excretion of amino acids may also occur.

0008 Radiographic evidence of rickets includes widening

of the growth plate of the long bones of both arms

and legs, and reduced bone density. In osteomalacia

of the adult, undermineralization of the bones may

manifest as pseudofractures, which are radiolucent

lines on the radiographs that mimic stress fractures.

However, the pseudofractures are usually bilateral

and often involve nonweight-bearing bones such as

the scapula.

Biochemical Changes

0009 Biochemical changes in most cases of rickets and

osteomalacia include decreased serum calcium and

phosphate levels because of the insufficient intestinal

absorption of these ions, increased serum parathyroid

hormone levels as a result of the reduced serum

calcium concentration, and elevated serum alkaline

phosphatase concentration. (Increased alkaline phos-

phatase results from increased osteoblastic activity

related to bone formation.) In cases of inadequate

supply of vitamin D or in liver disease, levels of

serum 25-hydroxyvitamin D (25(OH)D, a metabol-

ite) are invariably low, but the levels of 1,25(OH)

(the active hormone) may still be normal, depending

on the severity of the condition. Kidney disease will

lead to low serum 1,25(OH)

D levels, while serum

25(OH)D may be normal.

Vitamin D Insufficiency and Seasonal Variation in

Biosynthesis

0010A role for vitamin D insufficiency, rather than

a frank deficiency, in the elderly is now being

recognized as a contributing factor in low bone mass

and associated fractures in the aging population. The

age-related reduction in synthesis of vitamin D in

elderly women and men living in institutions or con-

fined to the home is often made worse by limited

exposure to direct sunlight and a decreased intake of

vitamin D. The dietary intake of vitamin D may be

particularly low in Europe, in comparison with the

USA where most dairy products are fortified with

vitamin D. Supplements of vitamin D and calcium

have proved effective at increasing bone mineral dens-

ity while decreasing the rate of hip and other nonver-

tebral fractures in nursing-home residents in Europe.

0011Large numbers of elderly residents in the northern

parts of North America and of Europe have been

shown to have depressed circulating levels of

25-(OH)D and, in some reports, also low serum con-

centrations of 1,25(OH)

D, particularly during

winter. Such seasonal differences have become well

established in these geographic regions, but

1,25(OH)

D insufficiency without symptoms of a

full-scale deficiency have only recently been docu-

mented. Because of the increasing life spans of so

many elderly people, and because so many of them

reside in nursing homes or similar facilities which

permit little exposure of residents to sunlight, frank

deficiency of vitamin D is likely to become more

common and may even reach epidemic proportions.

The public health consequences of osteomalacic bone

tissue and increased fracture incidence could be enor-

mous. Accordingly, some investigators have raised

tbl0002 Table 2 Characteristic clinical features and blood serum measurements in rickets and osteomalacia

Age Clinical features Blood serummeasurements

Children Skeletal deformations (rickets) Hypocalcemia

Impaired growth Hypophosphatemia

Undermineralized bone Secondary hyperparathyroidism

Low 25-hydroxyvitamin D

Elevated alkaline phosphatase

Adults Undermineralized bone (osteomalacia) Hypocalcemia

Fractures Hypophosphatemia

Low 25-hydroxyvitamin D

Elevated alkaline phosphatase

Elevated osteocalcin

This finding has not been consistently reported: see Vieth R (1990) The mechanisms of Vitamin D toxicity. Bone and Mineral 11: 267–272. Reproduced

from Cholecalciferol and Ergocalciferol/Rickets and Osteomalacia, Encyclopaedia of Human Nutrition, Sadler MJ, Strain JJ and Caballero B (eds), 1999,

Academic Press.

RICKETS AND OSTEOMALACIA 5003

questions about the adequacy of the current allow-

ances of vitamin D for the elderly.

Secondary Causes

0012 Causes of rickets and osteomalacia include not only

insufficient dietary intake of vitamin D or inadequate

exposure to sunlight, but also diseases that may

interfere with absorption and biotransformation of

vitamin D

or D

, as well as conditions leading to

decreased tissue responsiveness to the hormone and

to renal loss of phosphate (Figure 1). In fact, relatively

few cases of rickets in the western world today are

due simply to inadequacy of supply of vitamin D, and

most of these are due to strict dietary or religious

practices that involve vegetarian diets devoid of

sources of vitamin D or dress codes that prevent

exposure of the skin to sunlight.

0013 Patients suffering from malabsorption of fats may

have inadequate absorption of vitamin D from the

small intestine. Liver disease may interfere with the

conversion of vitamin D to 25(OH)D. Patients whose

kidneys have been removed or are severely diseased

will have decreased vitamin D hormone production

and may develop osteomalacia.

0014 Finally, inborn errors of metabolism may also

lead to rickets. Vitamin D-dependent rickets type

I is caused by a defect in the kidney enzyme

25(OH)D-1-hydroxylase, which is responsible for

the synthesis of 1,25(OH)

D. In vitamin D-dependent

rickets type II the receptor for 1,25(OH)

D is defect-

ive and cannot mediate the genomic action of the

hormone. In a third condition, called X-linked

hypophosphatemia, defects occur in the renal re-

absorption of phosphate, leading to low circulating

phosphate levels. Rickets and osteomalacia are pre-

sent in this condition despite the presence of normal

adult plasma 1,25-(OH)

D concentrations.

Public Health Consequences of Vitamin D

Deficiency

0015 Vitamin D, derived either from the diet or skin pro-

duction, has become an increasingly important mol-

ecule in human function because of the extended

longevity of human populations in many nations.

0016 Much greater efforts by health organizations are

needed to reduce the incidence and prevalence of

rickets and osteomalacia in both the developing and

the developed nations of the world. Assurance of

adequate calcium intakes must be the first priority,

and then emphasis needs to be placed on daily

sunlight exposure for infants and children.

0017 In recent years, supplements of vitamin D (400 IU

or greater) have been increasingly recommended for

elderly people, especially those who have become

institutionalized or shut-in because of limited mobil-

ity or confining conditions and diseases. Since the

elderly have declining capabilities of skin biosynthesis

and vitamin D conversion, larger doses of vitamin D

supplements are being recommended for this section

of the population. This recommendation is supported

by findings of low circulating blood concentrations of

25(OH)D or 1,25(OH)

D. Such low blood levels of

vitamin D metabolites are now being defined as char-

acteristic of vitamin D insufficiency rather than frank

deficiency.

0018Oral therapy with 1a-hydroxycholecalciferol has

become fairly widespread in the USA among elderly

subjects with low bone mass or fractures. The 1a

form must be converted in the liver to 1,25(OH)

by 25-hydroxylation. Dosages are generally low

because of concerns about toxic effects. The efficacy

of this therapy has not yet been fully evaluated.

Life-Cycle Changes in Vitamin D

Production and Metabolism

0019The skin production of vitamin D does not remain

constant throughout the life cycle, and it depends on

the changes in the skin tissue itself as well as the

environmental conditions in which people live. The

skin of older individuals has considerably less

capacity, for example, to produce vitamin D from

its precursor. In the elderly, the concentration of

7-dehydrocholesterol is diminished, and the rate of

conversion to vitamin D

is also reduced. When one

considers that the elderly usually have reduced sun

exposure as well, it becomes clear that they are at

great risk of developing vitamin D insufficiency

unless they have an adequate dietary supply of

vitamin D.

0020Alterations in the vitamin D endocrine system in

old age, such as a decrease in circulating 1,25(OH)

levels, have been implicated in the pathogenesis

of postmenopausal osteoporosis, because reduced

serum 1,25(OH)

D levels have been found in some

women afflicted with this condition. However, there

is no evidence indicating a general age-related de-

crease in serum 1,25(OH)

D concentration. A recent

study of a large group of healthy white adults ranging

in age from 20 to 94 years revealed no decline in

serum 25(OH)D or 1,25(OH)

D concentrations in

either sex. In another study, involving women aged

26–88 years, serum 1,25(OH)

D levels were actually

higher after age 65 years than in the youngest sub-

jects, but the rate of intestinal calcium absorption was

unaltered, suggesting decreased responsiveness to the

hormone with increased age followed by a compen-

satory increase in hormone synthesis.

5004 RICKETS AND OSTEOMALACIA

Special Problems of Low Vitamin D

Intakes

0021 Four categories of individuals who may have signifi-

cant deficiencies of vitamin D, whether from in-

adequate diet or insufficient skin exposure, are the

elderly, strict vegetarians (vegans), infants and young

children who have been maintained on breast milk for

periods of a year or longer, and migrant populations.

Each of these groups is characterized below.

Elderly

0022 Elderly individuals typically stay indoors most of the

time, and some may even be shut-ins who need

routine assistance with activities of daily living. It

is this latter group of elderly who are most likely

to be vitamin D-deficient and who need daily supple-

mentation of vitamin D, independent of season

and latitude of their homes, as well as calcium

supplementation. Low circulating serum 25(OH)D

concentrations provide a strong indication of second-

ary hyperparathyroidism and bone loss. Long-term

vitamin D treatment may improve bone health both

by enhancing intestinal calcium absorption and

reducing secondary hyperparathyroidism. An elderly

group of women living in nursing homes in Lyons,

France, had significant hypovitaminosis D that was

readily corrected by administration of a combination

of vitamin D (800 IU day

1

) and calcium (1200 mg

day

1

) for 18 months, at which time nonvertebral

fractures were significantly reduced.

Vegetarians

0023 Vegans are at risk of vitamin D deficiency if they have

little or no exposure to sunlight, because they typic-

ally consume unfortified plant foods. In addition to

the risk of osteomalacia, vegans have other nutri-

tional risk factors that put them at greater risk for

osteoporosis.

Long-Term Breast-Fed Infants and Young Children

0024 Rickets is occasionally reported in the USA in infants

who are breast-fed for long periods of time. Breast

milk is low in vitamin D and these nursing infants are

given no other source of vitamin D in their diets. The

risk of vitamin D deficiency is even greater in infants

with dark skin, as increased skin pigmentation has

also been established as reducing the skin’s biosyn-

thesis of vitamin D.

Migrant Populations at Risk

0025 Other groups at risk for vitamin D deficiency are

dark-skinned populations, especially Muslims, from

the Middle East or other Asian nations who have

migrated to the UK and other northern European

countries. These immigrants are vulnerable to vita-

min D deficiency because of inadequate exposure of

their skin to sunlight and little or no consumption of

vitamin D-fortified dairy products. Cultural practices

result in adults, as well as children, wearing clothing

that allows very little skin exposure to sunlight. Sup-

plementation with vitamin D and calcium is effective

in improving bone health in these populations.

Summary

0026While no accurate estimates of the prevalence of

either rickets or osteomalacia exist, hypovitaminosis

D is probably underdiagnosed in otherwise reason-

ably healthy adults, certainly in hospitalized adult

patients. The strong assumption is that vitamin

D consumption, and/or skin exposure for vitamin D

biosynthesis, are insufficient to permit adequate

formation of 25(OH)D, the circulating store of this

fat-soluble nutrient. The result of a low 25(OH)D

level is a fall in serum calcium and a continuous

elevation of serum parathyroid hormone concentra-

tion. (Parathyroid hormone is the culprit responsible

for increased bone turnover and decreases in bone

mass and bone density.) Correction of this problem

can be simply made by treatment with vitamin D

supplements, typically accompanied by calcium sup-

plements, and the consumption of vitamin D-rich

foods, fortified or not. Prevention of this condition

among older populations, however, appears currently

to be woefully inadequate.

See also: Aging – Nutritional Aspects; Bone; Calcium:

Physiology; Cholecalciferol: Properties and

Determination; Physiology; Inborn Errors of

Metabolism: Overview; Osteoporosis; Vegetarian Diets