What is vitamin D?
Vitamin D is actually a term for a group of hormones that are stored
mainly in the liver, as well as fat and muscle tissue. It is one of three
vitamins naturally manufactured by the body, and it is produced by a chemical
reaction to the ultraviolet radiation contained in sunlight.
Why do we need it?
Vitamin D increases the body's absorption and metabolism of calcium and
phosphorus. This makes it essential to maintaining strong, healthy bones
How much vitamin D should I take?
According to the National Academy of Sciences, the recommended daily
allowance (RDA) for vitamin D is as follows:
- Adult men: 200 international units (5 micrograms)/day
- Adult women: 200 international units (5 micrograms)/day
- Adults age 51-70: 400 international units (10 micrograms)/day
- Adults 71 and over: 600 international units (15 micrograms)/day
- Children aged 7-10: 200 international units (5 micrograms)/day
- Infants: 200 international units (5 micrograms)/day
- Pregnant/lactating women: 200 international units (5 micrograms)/day
What are some good sources of vitamin D?
Exposure to sunlight is the easiest way to build up stores of vitamin
D. By exposing the face, hands and forearms for between 15-20 minutes
two or three times per week, most people can manufacture all the vitamin
D they need.
Vitamin D is also found in a number of food products, most notably vitamin
D-fortified milk. Other sources include egg yolks, fish, cheese, fortified
cereals and liver.
What can happen if I don't get enough vitamin
Vitamin D deficiency can result in bone-related disorders such as rickets
in children and osteomalacia in adults. Vitamin D deficiency also increases
the risk of hip fractures in postmenopausal women, and has been linked
to higher incidences of prostate cancer and breast cancer.
What can happen if I take too much vitamin D?
High doses of vitamin D can be very toxic. In children, large doses can
cause mental retardation, stunted growth and kidney failure. In older
children and adults, too much vitamin D can result in weakness, anorexia,
nausea, diarrhea and changes in a person's mental state. With the exception
of kidney failure, low-calcium diets and withdrawal of vitamin D from
a person's diet can usually reverse these side-effects.
- Hypovitaminosis D in medical patients. New England
Journal of Medicine March 19, 1998.
- Safe amounts of vitamins. Health News August
- Vitamins, minerals, diet and prostate cancer. Harvard
Men's Health Watch May 1998.
- Vitamin D deficiency ups fracture risk. Reuters Health,
April 27, 1999.
- Vitamin D in infancy increases girls' bone density.
Reuters Health, December 28, 1999.