“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 mercola.com. 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:
- Vitamin D may not help to prevent the flu. See: Can Vitamin D Prevent the Flu?
- Take the recommended amount of vitamin D but don’t rely on it to prevent colds. See: Vitamin D Fails to Stop Colds
- Taking high doses of vitamin C does not lessen your risk for colds or respiratory infections. See: Does Taking Vitamin C Protect You From Colds?