New national guidelines for vitamin D intake highlight the need for the VITAL study
You may have heard about a new report from the respected Institute of Medicine (IOM), released in late 2010, that made recommendations about the amount of vitamin D that most Americans should consume. The IOM recommended 600 international units (IU) per day for people aged 1 to 70 and 800 IU per day for those aged 71 and older (an increase from the 400-600 IU/day previously recommended for adults at midlife and older).
To develop its recommendation, the IOM reviewed nearly 1000 scientific studies of vitamin D in relation to not only bone health but also many other health outcomes. It concluded that there is clear evidence that vitamin D has bone benefits but that current research is inconclusive as to whether higher vitamin D intake can cut the risk for cancer, heart disease, stroke, or other chronic diseases. We simply don’t know whether vitamin D supplements are beneficial in preventing diseases beyond osteoporosis or other bone disorders—nor do we know the amount of vitamin D that might be necessary to do so.
Because of this uncertainty, the IOM called for more research to determine (a) whether higher doses of vitamin D can lower the risk for cancer, heart disease, stroke, and other chronic illnesses and (b) whether such doses pose any health risks. The only sure way to identify the health benefits and risks of doses of vitamin D above the currently recommended amount is to carry out a large randomized clinical trial such as VITAL—that is, randomly assign one group of people to take a vitamin D supplement and assign another similar group of people to take a placebo and then track health outcomes in both groups for several years. Indeed, large trials of other widely used supplements have sometimes found benefits, but in other cases—such as with high doses of beta carotene, vitamin E, selenium, and even calcium—have debunked some health claims for these supplements and uncovered health risks that may not have otherwise been detected.
Given the current lack of evidence for non-bone benefits of vitamin D, the IOM based its vitamin D recommendation on the amount required for bone health only. The new guidelines call for a daily intake—or “recommended dietary allowance” (RDA)—that will meet the vitamin D needs of at least 97.5 percent of U.S. and Canadian residents. As noted earlier, these RDAs for adults are 600 to 800 IU per day. Although the sun activates vitamin D production in our skin, the IOM assumed little or no sun exposure because of differences in people’s ability to produce vitamin D—resulting from differences in skin color, as well as season of the year, location of residence, and use of sunscreen—and concerns about skin cancer. This means that the guidelines are adequate for everyone, including those living in the northern United States during the winter when the sun’s rays are weak.
The IOM’s report challenges the notion that many Americans are vitamin D deficient and cautions against the need for widespread blood tests for vitamin D. Many laboratories consider a vitamin D blood level of 30 or 40 nanograms per milliliter (ng/ml) to be best, but little research supports this claim. The IOM’s recommended intakes correspond to a vitamin D blood level of 20 ng/ml—again, sufficient to maintain strong bones for at least 97.5 percent of the U.S. and Canadian population. Most people meeting the intake guidelines do not need a vitamin D blood test.
The IOM also carefully reviewed available safety data on high-dose vitamin D supplements before raising the acceptable upper limit of daily intake to 4000 IU for adults, from the 2000 IU set previously. Extremely high intakes of vitamin D can lead to too much calcium in the blood and damage the kidney and heart, but whether moderately high doses of vitamin D have side effects is not yet clear.
Given the new IOM report (by the way, one of the study directors, Dr. JoAnn Manson, served on the IOM panel), we want to assure you that VITAL has been designed to ensure the safety of its participants, whether they are assigned to take placebo or pills containing vitamin D at a dose of 2000 IU per day. VITAL allows participants to take up to 800 IU of vitamin D per day in nonstudy supplements should they choose to do so. Together with intake from food (which averages 200 to 300 IU/day*), most participants will be able to consume at least 1000 IU of vitamin D daily, which is more than the new RDA. Thus, no participant should become vitamin D deficient due to participation in the trial, even if he or she is in the placebo group. Moreover, no participant who is assigned to take vitamin D will get too much unless he or she also takes a non-study vitamin D supplement containing more than the 800 IU per day allowed. In other words, participants in the vitamin D group who follow the study’s requirements will be consuming at most about 3000 IU of vitamin D per day, which is well within the IOM’s safety range.
VITAL is designed to answer the scientific questions regarding vitamin D that are considered important by the IOM: do vitamin D doses above the new RDA prevent cancer, heart disease, stroke, and other non-bone diseases? We are grateful that you have chosen to enroll in this landmark trial—and to take your study pills faithfully—to help us obtain much needed information about the health effects of vitamin D and omega-3 fatty acids (fish oil). Although the omega-3s haven’t made headlines as often as vitamin D lately, scientific research regarding their health benefits remains promising though inconclusive. VITAL is the first and only large trial to study the health effects of omega-3 supplements in people who are generally healthy.
* Natural food sources of vitamin D include fatty fish (such as salmon, sardines, and mackerel) and eggs. Vitamin D is also added to milk and some other dairy products, cereals, and orange juice (check product labels).