You Might Need Half as Much Vitamin D as Previously Thought

How much vitamin D should you really take? Not as much as you think. Peter Dazeley/Getty Images
How much vitamin D should you really take? Not as much as you think. Peter Dazeley/Getty Images


Your supplement bottle may soon last a little longer. The latest scientific research on vitamin D shows you may only need 400 International Units (IU) of the supplement daily, not the previously recommended 800 IU. Scientists from Creighton University School of Medicine in Omaha, Nebraska, presented this finding at ENDO 2017, the annual scientific meeting of the Endocrine Society.

In an earlier study conducted in 2007-2008, Dr. Christopher Gallagher, a professor at Creighton University and director of its Bone Metabolism Unit, looked at 163 healthy Caucasian postmenopausal women who were vitamin-D deficient. In a randomized double-blind study, the participants were given one of seven doses of vitamin D3: 400, 800, 1600, 2400, 3200, 4000 or 4800 IUs per day or a placebo for one year. Gallagher and his colleagues concluded that 800 IUs was recommended daily allowance (RDA) to get a sufficient amount of vitamin D.

Back then, the scientists analyzed the research participants' blood samples using an immunoassay test to come up with the 800 IU recommendation. Today, an improved measuring technique (called liquid chromatography mass spectrometry) is available. So, the researchers went back to their old samples and reanalyzed them with the updated technology. The results? They found we only need 400 IU of vitamin D to achieve the RDA, not 800. (The National Institutes of Health currently recommends 600 IUs for most adults.)

Vitamin D is good for bone health, immune function and a host of other uses. About 10 percent of Americans are vitamin D deficient. Unfortunately, few foods naturally contain this vitamin. The two best ways to get enough are through supplements and sun exposure, which helps your skin produce the vitamin.

However, exposing your bare skin to sunlight can increase the risk of skin cancer. It's also difficult to measure how much of the vitamin is being produced by sunlight, as it depends on the time of day, where you live and your skin color. Because of this, doctors typically advise to add vitamin D to your diet through vitamin D-fortified foods (like milk, orange juice and margarine) or supplements.

"Remember, this [new] RDA is for bone health only," Gallagher said in a press statement. "It may be different for other diseases. Although trials looking into cancer, diabetes, and other diseases are ongoing, we do not have information about this yet."