Vitamin D is essential to health, especially bone health. Exposure to sunshine helps the body produce vitamin D, and food sources include milk, eggs, fish and cod liver oil. Health organizations are reassessing recommended vitamin D intakes, which some researchers say are too low. Vitamin D deficiency can cause or contribute to disorders such as rickets and osteoporosis. Because the body stores vitamin D, getting too much from foods or supplements can be harmful.
Sources of Vitamin D
The biggest natural source of vitamin D is sunlight. As little as 10 minutes of sun exposure a day can help your body produce adequate amounts of vitamin D. Fortified milk provides much of the vitamin D in many people's daily diets. Fatty fish and fish oils are also good sources. Cod liver oil is a very rich source -- 1 tablespoon provides 1,360 IU of vitamin D.
Recommended Daily Intakes
The United States and Canada have set the recommended daily intake of vitamin D for children and adults up to 50 years old at 200 International Units. Recommended vitamin D intake is 400 IU for adults aged 51 to 70, and 600 IU for adults over 70. Some researchers and organizations, including biochemist Anthony Norman, a leading expert on vitamin D, and Osteoporosis Canada, believe the recommended intakes of vitamin D are too low and that the daily intake for adults should be 2,000 IU.
Deficiency
Because vitamin D helps your body absorb calcium, too little puts you at greater risk of bone loss, leading to osteoporosis. Children who lack enough vitamin D can get rickets. Some researchers, including Norman, emphasize that vitamin D may play a role in reducing the incidence of other disorders such as cancer, type 1 diabetes, high blood pressure, cardiovascular disease and obesity.
Toxicity
The U.S. and Canada have set the safe upper intake of vitamin D at 2,000 IU daily. Some scientists think the safe levels can be much higher, but the U.S. National Institutes of Health, or NIH, says there aren't enough long-term studies to support that. Effects of vitamin D toxicity can include nausea, vomiting, weakness and weight loss. More dangerously, vitamin D in excess can raise calcium blood levels too high, leading to mental changes and abnormal heart rhythms. In one study, women who took both calcium supplements and 400 IU of vitamin D daily showed an increased risk of kidney stones, according to the NIH.
Who's at Risk?
People who are not exposed to enough sunlight may risk vitamin D deficiency. Osteoporosis Canada says that people who live above 35 degrees north latitude -- the northern United States and all of Canada -- risk vitamin D deficiency because the winter sun doesn't provide enough ultraviolet light. Taking too much vitamin D from supplements, such as cod liver oil, over a long period can put you at risk of vitamin D toxicity. According to the NIH, you're very unlikely to get too much vitamin D from overexposure to sunlight, since your body adjusts the level of the vitamin as needed.
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