hypophosphatemia. Both of these are characterized by
abnormally low levels of phosphate in the blood.
Normal vitamin D requirements
The United States Institute of Medicine (IOM) of
the National Academy of Sciences has developed values
calledDietary Reference Intakes(DRIs) forvitamins
andminerals. The DRIs consist of three sets of num-
bers. The Recommended Dietary Allowance (RDA)
defines the average daily amount of the nutrient needed
to meet the health needs of 97–98% of the population.
The Adequate Intake (AI) is an estimate set when there
is not enough information to determine an RDA. The
Tolerable Upper Intake Level (UL) is the average max-
imum amount that can be taken daily without risking
negative side effects. The DRIs are calculated for chil-
dren, adult men, adult women, pregnant women, and
breastfeedingwomen.
The IOM has not set RDA values for vitamin D
because of incomplete scientific information and varia-
bility in the amount of vitamin D the body makes when
the skin is exposed to sunshine. Instead, it has set AI
and UL levels. Recently the UL level has become some-
what controversial and has been challenged by some
researchers as being set too low. AI and UL levels are
measured in both weight (micrograms or mcg) and
international units (IU). The IU measurement is the
measurement used on dietary supplement labels. For
vitamin D, 1.0 mcg equals 40 IU.
The following are the AIs and ULs for vitamin D
for healthy individuals:
infants 0–12 months: AI 200 IU or 5 mcg; UL 1,000
IU or 25 mcg
children 1–18 years: AI 200 IU or 5 mcg; UL 2,000
IU or 50 mcg
adults 19–50 years: AI 200 IU or 5 mcg; UL 2,000 IU
or 50 mcg
adults 51–70 years: AI 400 IU or 10 mcg; UL 2,000
IU or 50 mcg
adults 71 years and older: AI 600 IU or 15 mcg; UL
2,000 IU or 50 mcg
pregnant and breastfeeding women: AI 200 IU or 5
mcg; UL 2,000 IU or 50 mcg
Exposing the face, arms, and legs to sunshine for 15
minutes three or four times a week meets the dietary
requirements for vitamin D for people with fair skin
much of the time. However, people who live north of
40 latitude (approximately a line that extends from Phil-
adelphia to San Francisco) may not get enough sun expo-
sure to meet their dietary needs during winter months.
Dark-skinned people may need to spend triple the amount
of time in the sun as fair-skinned people to synthesize
adequate amounts of vitamin D, since the increased
amount melanin pigment in dark skin slows vitamin D
production. Using sunscreen with an SPF of 8 or higher
also slows the production of vitamin D in the skin.
Vitamin D is not found in large amounts in many
foods. However, since the 1930s vitamin D has been
added to about 99%: of all milk, and to some breakfast
cereals, bread, orange juice, and infant formula. In
addition, the Food and Drug Administration requires
all foods containing olestra, a compound that reduces
fat absorption, to be fortified with the fat-soluble vita-
mins A, D, E, and K.
The following list gives the approximate vitamin
D content for some common foods:
cod liver oil, 1 Tablespoon: 1,360 IU
salmon, cooked, 3.5 ounces: 360 IU
mackerel, cooked, 3.5 ounces: 345 IU
tuna, canned in oil, 3 ounces: 200 IU
milk, any type fortified, 1 cup: 100 IU
orange juice, fortified, 1 cup: 100 IU
cereal, fortified, 1 serving: 40 IU (average, serving
sizes vary)
egg, 1 whole: 20 IUPrecautions
Vitamin D deficiency
Vitamin D deficiency results in rickets in children
and osteomalacia in adults. Rickets is a condition in
which the bones do not harder because of a lack of
calcium deposited in them. Instead they remain soft
and become deformed. Osteomalacia is a weakening
of bones in adults that occurs when they are broken
down (demineralized) and calcium in the bones is
returned to the blood. Vitamin D deficiency also can
cause joint and muscle pain, and muscle spasm. Less
severe cases can result inosteoporosisin older adults.
The vitamin D fortification program, along with
the popularity of daily multivitamins, has greatly
reduced the number of people in the United States
who are vitamin D deficient. However some groups
remain at risk of vitamin D deficiency. These include:
infants who are exclusivelybreastfed. Breast milk pro-
vides only about 25 UL of vitamin D per quart (liter).
The American Academy of Pediatrics recommends
vitamin D supplements beginning no later than 2
months of age for babies who are only fed breast milk.
institutionalized or homebound people who rarely
go outside. One study found that 60% of nursing
home patients were vitamin D deficient.Vitamin D