Function:
Although a number of compounds have vitamin D activity,
the two most important ones are vitamins D2(ergocalciferol)
and D3(cholecalciferol).
Vitamin
D is required for the maintenance of bone metabolism and
for proper balance and utilization of calcium and phosphorus
in the body. It also regulates the absorption of calcium
and phosphorus from the small intestine.
Recommended
Dietary Allowance:
For
adults 19 to 51 years 5 mcg. For adults 51 to 70 years 10
mcg, and over 70 years 15 mcg per day.
One
mcg of vitamin D3, cholecalciferol, equals 40 IU.
Deficiency:
Vitamin D deficiency results in rickets in children and
osteomalacia (a relative deficiency of calcified bone) in
adults. It also plays a significant role in the development
of osteoporosis.
Sources:
Vitamin
D occurs in very few foods including liver, eggs, and fatty
fish. Milk is fortified with 10 mcg (400 IU) per quart.
The
primary source is produced by the action of sunlight on
7-dehydrocholesterol in the skin. There is a built-in production
limitation in those who are exposed to large amounts of
sunlight. Above and below 40 degrees north and south latitudes
synthesis from the skin is almost zero for three to four
winter months and for six months at more extreme latitudes.
Clothing and sunscreen also play a significant role in reducing
vitamin D production.
Over
the age of 65 the capacity to produce vitamin D is reduced
by four times the ability at age 20 or 30.
Toxicity
and UL:
Too
much vitamin D possibly results in increased calcium absorption
from food and increased release from bone. It may result
in excessive thirst and urination and in the extreme kidney
stones and calcium deposits elsewhere in the body.
A review
of the world literature printed in the American Journal
of Clinical Nutrition recently suggested that side effects
were rare or absent even with very large doses.
Very
large amounts of vitamin D have been taken as a component
of cod-liver oil worldwide for many years.
The
UL is 50 mcg (2,000 IU) per day.
Recommendation:
Some reports suggest that 1,300 to 3,800 IU daily might
protect against osteoarthritis, multiple sclerosis, breast,
ovarian, prostate, colorectal cancers and hypertension.
I recommend
supplementation with 5 to 15 mcg (200 to 600 IU) per day
to assure adequate intake of this important vitamin.
