Almost 80 million Americans don't have low vitamin D levels after all, an expert group says. The new, lower guidelines on vitamin D come from the Institute of Medicine. This is an independent group that provides research-based advice on medical care. Current guidelines don't agree on what blood level of vitamin D is too low. For example, the Endocrine Society says that people should have at least 30 nanograms of vitamin D per milliliter of blood (ng/ml). Anyone with lower levels may need vitamin D pills, the group says. The new Institute of Medicine guidelines say that 20 ng/ml is enough. An estimated 78.7 million American have levels between 20 and 30. The new study included more than 15,000 adults. Information about them came from a major health survey. This was compared with a national death registry. Death rates were much higher with vitamin D levels of less than 12 ng/ml than with levels of 24 to 30. But there was little difference for people with vitamin D levels in between. The journal PLoS One published the study online. HealthDay News wrote about it October 24.

By Robert H. Shmerling, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Vitamin D is an important nutrient. But just how important is it? We know it's vital for helping the body build strong bones and absorb calcium. But in recent years other health benefits have been suggested.

For example, there is some evidence that vitamin D may help to:

• Prevent cancer
• Improve immune function
• Keep joints healthy
• Improve brain function
• Lower the risk of heart disease and death

These are difficult claims to prove. Most of them come from studies linking low levels of vitamin D with an increased risk of disease. But it's possible that people with low vitamin D also smoke more, exercise less or have other causes for their higher rates of disease and death.

Interestingly, no one seems sure just how much vitamin D is enough. Experts have looked at vitamin D in the diet, pills of various types and doses, and the results of blood tests. They have not always agreed about what the results mean. Our hospital’s laboratory considers a normal blood vitamin D level as 20 nanograms per milliliter (ng/ml) or higher. But standard guidelines suggest that 30 ng/ml or above is better.

So should you worry if your vitamin D level is 26 ng/ml? According to a new study, the answer is no. And neither should the nearly 80 million people in the United States with similar levels.

Researchers affiliated with the Institute of Medicine reviewed data from thousands of studies. The institute is an influential group that works to improve health care. Researchers also sought opinions from scientists who study vitamin D. They reached these conclusions:

• The primary benefit of vitamin D is related to its effects on bone health. The other proposed benefits are much less certain.
• A blood vitamin D level of 20 ng/ml or higher should be considered normal.
• About 40% of adults in the United States have vitamin D levels between 20 ng/ml and 30 ng/ml. That's 78.7 million people who may receive treatment they don't need to increase their levels.

Why does this matter? Changing definitions of "normal" can have huge effects. Billions of dollars are spent on vitamin D tests and pills. And then there's the worry of having "abnormal" results or the downside of changing your diet to one you may like less.

Fortunately, vitamin D in the diet and in pills is quite safe. Recommended doses rarely cause big side effects. However, excessive doses can be dangerous. And there is the cost of pills to consider.

What Changes Can I Make Now?

While vitamin D is important, recent claims about its health benefits may not all hold up. The ideal amount of vitamin D in the blood is not entirely clear. But you can take steps to avoid having low levels (less than 20 n ml).

• Increase vitamin D in your diet. Some good sources are:
  
  • Dairy products, such as low-fat or skim milk or low-fat yogurt
  • Some fish, such as swordfish or salmon
  • Fortified foods, such as cereals and orange juice


• Get some sun. Just 10 to 15 minutes a day may be enough. Too much sun increases the risk of skin cancer and other skin problems.



• Take vitamin D pills. This is especially important if you have factors that increase your risk of low vitamin D levels. Factors include low vitamin D in your diet, minimal time in the sun or a medical condition that reduces absorption of nutrients. For most people, 800 to 1,000 units per day is enough. Avoid megadoses of vitamin D.



• Get your blood level checked. This may not be needed as a routine test. However, it may be a good idea if you (or your doctor) are unsure whether you should take vitamin D pills. And testing is recommended if you have a condition (such as osteoporosis) in which it is important to avoid low vitamin D. Make sure the test checks the 25-hydroxy-vitamin D level. This is the most accurate measure of the body's vitamin D status.

It may also be a good idea to look again at your intake of calcium, which is also important for bone health. This study suggests that many people who take vitamin D pills now may not need them. If you aren't sure about any products you're taking, talk to your doctor about the pros and cons of stopping them.

What Can I Expect Looking to the Future?

This study is not likely to be the last word on how much vitamin D is enough. Ongoing studies should clarify:

• The role of vitamin D in health and disease
• The ideal blood level of vitamin D and which people should be tested
• The best candidates for treatment with vitamin D pills

In the meantime, watch for news about vitamin D. What's considered normal could change again.