Vitamin D and Calcium: Are We Getting Enough?
A new report revises daily intake guidelines for these nutrients, based on a thorough review of existing research.
Nearly all Americans get enough vitamin D through diet and exposure to sunshine, the report says, and there isn’t yet enough evidence that vitamin D offers protection against cancer, diabetes, and heart disease, or plays a role in a host of other ailments such as multiple sclerosis, as some studies have suggested. The IOM report, which sets new dietary recommendations for calcium as well as vitamin D, warns that some people may face health risks from getting too much of these nutrients.
The IOM is the expert group within the National Academy of Sciences that provides independent, evidence-based advice on major health issues to policymakers, professionals, and the public. This IOM study was sponsored by the U.S. departments of Health and Human Services, Agriculture, and Defense, and by Health Canada, a department of the Canadian federal government.
As the vitamin D trend took hold, many doctors began routinely testing their patients for vitamin D deficiency and recommend vitamin D supplements. Many people take 1,000 or 2,000 international units (IUs) of vitamin D a day, and some take as much as 5,000 or 10,000 IUs.
“It’s all over the Internet. There are now 5,000 IU capsules you can find in WalMart. You can get anything you want,” says IOM vitamin D committee member Clifford E. Rose, MD, senior scientist with the Maine Medical Research Institute in Scarborough.
The trend has been fueled by research suggesting that vitamin D deficiency may play a role in a range of diseases and conditions, including autism, mental illness, cancer, heart disease, diabetes, fibromyalgia, and autoimmune diseases. But, the committee warns, high levels of vitamin D could cause long-term harm to your health.
“Increasing your blood level of vitamin D not only doesn’t offer you protection against cancer or heart disease, it may increase your risk of those diseases,” Dr. Rose says. “The idea that more is better is wrong, and the idea that it’s not harmful to take all these supplements may also be wrong.
Rose notes that he and other committee members were “totally surprised” by their findings because many of them had bought into the idea that extra vitamin D could improve health.
“I went into this with very preconceived ideas that we are all vitamin-D deficient,” he says. "We all believed it. We were very aggressive about supplementing. We were very surprised to see that the higher levels may cause some problems.”
How Much Vitamin D and Calcium Do You Need?
Most people up to age 70 need only 600 international units (IUs) of vitamin D per day; those older than 70 may need up to 800 IUs, the committee determined. Taking more than 4,000 IUs of vitamin D per day may be associated with a higher risk of death and chronic disease.
Guidelines for calcium intake vary by age.
Children and adolescents should get:
- 700 milligrams (mg) per day – ages 1 through 3
- 1,000 mg per day – ages 4 through 8
- 1,300 mg per day – ages 9 through 18
- 1,000 mg per day – ages 19 through 50 for women and 19 through 71 for men
- 1,200 mg per day – age 51 and older for women and 71 and older for men
“There is abundant science to confidently state how much vitamin D and calcium people need,” says Catharine Ross, chair of the committee that issued the report, and chair of the department of nutritional sciences at Pennsylvania State University, University Park.
Faulty Laboratory Testing Procedures?
The IOM group also took issue with vitamin-D deficiency testing in labs. Test procedures are not standardized, and results vary widely among laboratories. As a result, many people are wrongly told they are vitamin-D deficient. Many laboratories find people deficient in vitamin D if blood levels are below 30 nanograms (ng) of vitamin D per milliliter of blood. The cutoff should be closer to 20 ng per milliliter, says committee member Glenville Jones, MD, head of the biochemistry department at Queen’s University in Kingston, Ontario. “In the past three or four years, there’s been a slow ramping up of the threshold or cutpoint.”
In addition, says committee member Steven K. Clinton, MD, professor of internal medicine at Ohio State University in Columbus, routine vitamin D testing is largely unnecessary because most people are getting enough of these nutrients.
As vitamin D and calcium are added to more prepared foods and rates of supplement use continue to rise, chances are increasing that some people will take too much of these nutrients. Too much calcium has been associated with kidney stones, while excessive vitamin D can damage the kidneys and the heart.
Vitamin D and Calcium: More Clarity From Further Research
The IOM committee examined nearly 1,000 studies on the possible protective effects of vitamin D and heard testimony from scientists and others with an interest in the topic. The committee found that study results to date have been conflicting and mixed, and that more research is needed.
“We are still very enthusiastic about this molecule [vitamin D] that regulates hundreds if not thousands of genes in the body," Dr. Clinton says. “What’s missing is the translation of basic science into a public health recommendation. We can’t make that leap at this time.”
Plenty of evidence supports the role of vitamin D and calcium in promoting skeletal growth and maintaining bone health, the committee found. The body produces vitamin D from exposure to sunlight; vitamin D and calcium are found in some fish, dairy foods, and fortified foods such as cereal, juices, and milk.
The IOM committee hopes the new report will reduce confusion about vitamin D and calcium needs, and discourage doctors from relying too heavily on laboratory tests to recommend vitamin D supplements until new testing standards have been developed.
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