Vitamin D: How much is too much?

Is it possible to take too much vitamin D? I know vitamin D is important, but I wonder if too much is dangerous?

- No name / No state given

Answer

Vitamin D is an essential nutrient for your entire body. Still, it's possible to have too much of a good thing.

Vitamin D has long been known to promote healthy bones. Some research suggests that vitamin D may also help prevent certain cancers, as well as diabetes, high blood pressure, multiple sclerosis and various other conditions.

Your body produces vitamin D naturally when you're exposed to sunlight, as long as you're not wearing sunscreen. The best food sources of vitamin D include salmon, mackerel, sardines, tuna and fortified milk. Cod liver oil also contains large amounts of vitamin D.

Recent research suggests that many people may not be getting enough vitamin D. More exposure to sunlight can help, but this increases the risk of skin cancer and other skin problems. The National Academies of Sciences currently recommends 200 international units (IU) of vitamin D a day for children and adults up to age 50 and 400 to 600 IU for adults older than age 50. However, many researchers now question whether these levels are adequate and assert that a daily intake of 800 to 1,000 IU would benefit many people. In fact, the American Academy of Pediatrics recommends 400 IU a day for children, beginning the first few days after birth.

If you're not getting enough vitamin D, your doctor may recommend vitamin D supplements. Still, moderation is important. You're unlikely to get too much vitamin D from the food you eat, and prolonged sun exposure doesn't seem to cause vitamin D toxicity. Over time, however, megadoses of vitamin D supplements can cause nausea, vomiting, poor appetite, constipation, weakness and weight loss. More seriously, excessive doses of vitamin D can raise the level of calcium in your blood — which can cause confusion and changes in heart rhythm. Generally, the upper limit for vitamin D is 2,000 IU a day.

If you're concerned that you're getting too little — or too much — vitamin D, contact your doctor. He or she may recommend a blood test to check the level of vitamin D in your blood.

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