Does Vitamin D Boost Your Immune System?

“Optimizing your vitamin D levels is one crucial component” of a robust immune system and “improves your immune system by 3-5 times,” according to Joseph Mercola on his popular Web site Too bad people who take vitamin D are no less likely to get sick.


Since 2012, three trials in the United States and Western Europe have given 1,650 people either 1,000 IU to 6,800 IU of vitamin D or a placebo every day for up to 18 months. (The DV is 400 IU.) In none of the studies did the vitamin D takers report any fewer respiratory infections. And in the two studies that looked, the vitamin takers’ symptoms were no milder and their illnesses were no shorter after they did get sick.

In the most recent study, “vitamin D supplementation conferred no significant protection against upper respiratory infections, including during two winters,” says Judy Rees of the Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire.

Two large trials are now testing vitamin D on colds and the flu (and other outcomes). But so far, the evidence is not convincing.

Sources: Scand. J. Infect. Dis. 44: 126, 2012; JAMA 308: 1333, 2012; Clin. Infect. Dis. 57: 1384, 2013.


Other relevant links:

4 Replies to “Does Vitamin D Boost Your Immune System?”

  1. Healthy Sun Exposure Is Your Best Source of Vitamin D is what Dr.Mercola stresses mostly on his website, not supplementation in a pill. As a faithful follower of both your newsletter and Dr. Mercolas, I quite frankly cant believe you guys missed that most important point.

  2. As vitamin D3 is fat soluble, unless they explicitly gave the vitamin D3 with a meal or vegetable oil, it won’t have any big effect because it will wash out of the body very quickly. Everyone I know who’s taken high D3 with a meal saw a 90% reduction in viral infections!

  3. I doubt most people take it in order to avoid colds and flu. Many of us with autoimmune disease have been advised to take the supplement because low levels of Vitamin D are a risk factor for certain illnesses. You can’t just keep having a blood test for your serum vitamin D level. So what’s the harm in taking a small dose, especially in winter?

    1. From Nutrition Action Healthletter: Many people need to take vitamin D supplements to achieve the recommended amounts because few foods are rich in this vitamin and getting enough sun exposure is difficult for some people, especially during the winter. We addressed the issue of whether vitamin D can prevent colds or the flu because some vitamin companies are suggesting it can.

Leave a Reply

Your email address will not be published. Required fields are marked *