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Getting enough vitamin D
It's estimated that 30-50% of Americans suffer from vitamin D deficiency. The human body produces vitamin D, which is actually a hormone, when exposed to sunlight. However, during the winter, it is impossible to get enough exposure anywhere north of San Francisco or Philadelphia. People in southern states who slather on sun block or who stay indoors most of the time may not be getting enough either. The same goes for people who are housebound due to illness or whose work keeps them inside all day. In addition to lack of sunshine, other conditions may increase likelihood of vitamin D deficiency:
Infants who are exclusively breastfed. Mother's milk may not provide sufficient levels. The American Academy of Pediatrics recommends a supplement of 400 IU per day.
Older adults. The elderly do not synthesize vitamin D as effectively as younger people and tend to spend more time indoors.
People with dark skin. The pigment melanin can reduce the body's ability to produce vitamin D from sunlight.
Obese people. Body fat alters the way vitamin D is released into the system.
Choosing a vitamin D supplement
If you are shopping for a supplement, research suggests that vitamin D3 is more effective than vitamin D2. Food sources rich in vitamin D include cod liver oil, fatty fish (such as mackerel), eggs, and fortified milk and orange juice.
There is some debate over how much vitamin D to take. The National Institutes of Health recommends 600 IU per day for adults but some experts say that taking a supplement that contains between 1000-2000 IU can be beneficial. Its important to stay within the appropriate range--there is a toxicity risk at over 10,000 IU. The best way to determine how much you might need is to have your physician administer a simple blood test and make a recommendation based on the current level in you system.
