How Much Vitamin D Should You Get?

 

Roughly one in five American adults takes vitamin D and calcium supplements. But a long-awaited report released last month proclaimed the pills largely unnecessary for healthy people. The supplements provide no additional benefit according to the best available research, and too many can be dangerous, the report said. So, should you strike them from your daily regimen? The answer depends on your health, your beliefs, your fears, and your choice.

We asked vitamin D experts across the country to answer questions about the report and explain the controversy over its findings.

Why is the report’s recommendation controversial?

Research over the last five years has increasingly suggested that vitamin D deficiency plays a role in cardiovascular disease; autoimmune disorders such as lupus, diabetes, and rheumatoid arthritis; brain disorders such as depression, dementia, and Alzheimer’s disease; and cancers, particularly colon cancer. Many experts had hoped and expected the panel to recommend that people take vitamin D supplements to protect against deficiency. The Institute of Medicine panel reported that it is not clear how much vitamin D is needed to protect against these disorders or that vitamin D deficiency is widespread. Everyone agrees that vitamin D, combined with calcium, is crucial for strong bones.

How much vitamin D is the right amount?

It’s still an open question how much vitamin D we need for optimal health. The panel recommended that people reach at least 20 nanograms of vitamin D per milliliter of blood. Since the vast majority of Americans and Canadians already achieve that level through their diet and exposure to sunlight (and most also get enough calcium), the panel decided that supplements are unnecessary for most people. Other scientists believe that people should reach a blood level of at least 30 nanograms/ml of vitamin D for health benefits beyond bone health. That level is much harder to reach without supplements.

Why was the committee so conservative in its recommendations?

In the past, researchers have been very excited about other vitamins and minerals — including vitamin E, beta carotene, and selenium — only to find when they did more definitive studies that such supplements were not helpful and might even be dangerous. The committee said it was only willing to rely on data that proved that the vitamins caused a positive benefit — a standard that is very hard to reach, and that has only been achieved related to vitamin D’s role in bone health.

Why does the panel’s recommendation matter?

The panel’s conclusions will be used by federal, state, and local agencies to plan government-run nutrition programs such as school lunches and Meals on Wheels for senior citizens. Recommendations such as these are also used to set the federal Recommended Daily Allowances that appear on food nutrition labels.

How do we get vitamin D and calcium?

Calcium is abundant in dairy products, including milk and yogurt, which are usually also fortified with vitamin D, because D helps bones absorb calcium. Vitamin D is plentiful in fatty fish, including canned tuna, salmon, and sardines, a serving of which provides about 300 international units — about half the daily amount the panel recommends for people under 70. Most people find it challenging to get the full Recommended Daily Allowance of vitamin D from their diet alone. But the adequate levels found in most people’s blood also reflects the vitamin D we manufacture when exposed to sunlight.

What do vitamin D and calcium do in the body?

Recent research shows that there are vitamin D receptors in nearly every organ and many different cell types, meaning the nutrient is essential to a variety of functions. Calcium is also used by every cell in the body to allow substances to pass in and out of cell membranes. The two work together to make strong bones.

Does the need for these nutrients change as we age?

Members of the panel said they had assumed that children would need more vitamin D than adults, but they found that the strongest evidence suggests that the same 600 IU a day is good for everyone under the age of 70. People over 70 need 200 IU a day more, according to the panel. For calcium, the committee worried that two groups may not be getting enough calcium in their diets: girls 9 to 18, who they said should get 1,100 mg/day; and postmenopausal women, who they said should get 1,000 mg/day. For all other adults, the panel recommended 800 mg/day.

Do different people need different amounts of vitamin D?

Yes. People with dark skin do not absorb vitamin D as efficiently from sunlight, and people who live in northern climates, such as New England, don’t get enough ultraviolet B rays from the sun during the winter, so both groups are at higher risk of being deficient. The same is true for overweight and obese people, who make less vitamin D when exposed to the sun than people of normal weight, and for older people, people with absorption problems, people whose medications cause deficiencies, and those who avoid sun because of fear of skin cancer. Sunscreen blocks the ultraviolet rays that allow the skin to manufacture vitamin D. The committee assumed that people get very little sun exposure, so to reach its recommended amount, you do not need to take more vitamin D in winter or if you live in the northern United States.

Can you get too much vitamin D?

Yes. One of the committee’s key recommendations was that amounts over 4,000 IU per day pose possible health risks, including kidney and tissue damage. Other researchers have criticized this upper limit, saying it should really be set much higher, at about 10,000 IU per day.

What about calcium?

Walter Willett, a Harvard nutrition researcher, said the panel went too far in recommending 1,000-1,200 mg of calcium a day for all adults. He said half that amount — the equivalent of one to two glasses of milk a day — is sufficient to protect bones. People who live in countries where dairy is not consumed regularly still have healthy bones, he said. Too much calcium (see the above chart) can cause kidney stones and increase the risk of heart disease, fatal prostate cancer, and possibly ovarian cancer.

Who should get tested for vitamin D deficiency?

People at high risk of deficiency may want to get a blood test to check their vitamin D level. (The test itself is getting more reliable, but the panel also called for the government to issue guidelines for standardizing testing, so that a reading from one lab would mean the same as a reading from any other lab.) Tests cost about $120 and are usually covered by insurance.

Is more research needed?

Yes, say both panel members and critics. Panel member Dr. JoAnn E. Manson of Brigham and Women’s Hospital is launching a five-year trial of 20,000 subjects to see whether supplements of 2,000 IU of vitamin D per day, along with fish oil, offer benefits beyond bone health. To learn more about this trial, go to www.vitalstudy.org or call 800-388-3963.

So, what’s the bottom line? How much vitamin D do I need?

There is no clear answer. If you’re the type of person who needs solid proof of effectiveness before you put something in your body, then you probably get enough vitamin D in your diet to meet your basic needs — at least according to currently available evidence. If you like to hedge your bets and can afford it, you may want to consider supplements, at least until the next few rounds of major research are completed. The dose you take is more guesswork than science, but anything under 4,000 IU of vitamin D is almost definitely safe, and far more might be, too.

Karen Weintraub can be reached at karen @karenweintraub.com.

Interviewed for this story :

-From “More? Or less? Experts disagree about how much vitamin D and calcium you should get” by Karen Weintraub , Globe Correspondent , The Boston Globe, December 20, 2010 at http://www.boston.com/news/health/articles/2010/12/20/panel_recommends_less_supplementing_of_calcium_and_vitamin_d_some_argue_for_more_research/, retrieved 12/20/10.

 

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