Your body manufactures and stores vitamin D, which forms under your skin during exposure to strong sunlight. Vitamin D is also found in foods like fortified milk and salmon. Storing vitamin D in the body allows people to survive in dark winter climates without running short. Moderate doses of vitamin D taken as supplements make up for any shortages that modern lifestyles create. When your body absorbs massive doses of vitamin D, health problems follow.
Unsafe Doses
Your body absorbs vitamin D with such efficiency that taking extremely large doses could kill you. One study investigated the practicality of taking enough vitamin D for an entire year in one dose, according to the Harvard School of Public Health. Older women participating in the 5-year trial took 500,000 IU of vitamin D once per year. Although vitamin D normally prevents bone diseases, the large dose increased the number of falls the women suffered and put them at greater risk of bone fractures. You could still suffer ill effects by taking much smaller daily doses of vitamin D over the long term.
Safe Upper Limits
Anyone over 9 years old can take as much as 4,000 IU of vitamin D daily without health risk, according to the Office of Dietary Supplements of the National Institutes of Health. The maximum safe dosage is less for younger children. Infants 6 months old or younger should take no more than 1,000 IU. The Food and Nutrition Board set these upper limits conservatively, since the true safe maximum dose still isn't known. Uncertainties remain about minimum needs as well. Your needs depend not only on your age but on details of lifestyle such as where you live, what you wear and how much time you spend in the sun.
Recommended Intake
Exposure to sunlight once provided most of the vitamin D individuals needed, but modern lifestyles often make that impractical. Increased risk of skin cancer could cause you to spend more time indoors and shield yourself from UV light while outside. Vitamin D supplements make up for the lack of sun exposure. Anyone between 1 and 70 years old can take 600 IU of vitamin D daily. If you're over 70, you need at least 800 IU every day. The American Academy of Pediatrics recommends that children under 1 year old take 400 IU daily to prevent vitamin D deficiency disease such as rickets.
Other Opinions
In some instances, you might need more vitamin D than the amouts set by the Food and Nutrition Board. Vitamin D protects you against many diseases including osteoporosis, cancer and influenza. Adequate vitamin D intake maintains bone and muscle strength and reduces the incidence of falls among older people. You'll need from 800 IU to 1,000 IU of vitamin D every day to ensure health benefits, according to the Harvard School of Public Health. The Linus Pauling Institute recommends even more -- 2,000 IU daily for healthy adults. Ask your doctor for advice about the right dosage for you.
References
- Harvard School of Public Health: Vitamin D and Health
- Harvard School of Public Health: Avoid Super High Doses of Vitamin D
- Office of Dietary Supplements: Vitamin D
- Medill Reports -- Chicago; Pediatricians Recommend Double Dose Vitamin D for Infants and Kids; Jenelle Molenaar; October 2008
- Linus Pauling Institute; Micronutrient Information Center -- Vitamin D; Jane Higdon; March 2004
Member Comments