Vitamin D: A Supplement That May Prevent the Flu

Written By: Gloria Tsang, RD

Title: Founding Registered Dietitian

Alumni: University of British Columbia

Last Updated on:

H1N1 flu cases are putting us on guard. You’ve already added immune-boosting foods like citrus, yogurt, and mushrooms to your diet. But what about supplements? You’ve heard about Vitamins C and D, and zinc lozenges, so which ones actually may prevent flu?

Vitamins Commonly Associated with Flu

Vitamin C

A systematic review has found evidence that high-dose Vitamin C reduces the duration of symptoms in people with upper respiratory tract infections. However, not all studies generated a similar result. Therefore, it is not generally recommended to take Vitamin C supplements routinely, but you may try them with the onset of a flu.


Zinc lozenges were very popular in the 1980s and 90s, but it turns out they’re a thing of the past. Scientists from the Pittsburgh Medical Center conducted a review in 2007 of studies that investigated the effectiveness of zinc. They found that only one study had shown benefits, four subsequent studies showed no benefits, and four were biased.

Vitamin D

This sunshine vitamin continues to surprise us. A 2007 study found that subjects taking daily Vitamin D supplements were 3 times less likely to report cold and flu symptoms. A higher dose (2000 IU/day), given during the last year of the study, resulted in virtually no reports of cold or flu symptoms.

Why You May Want to Give Vitamin D a Try

Last year, the American Pediatric Society doubled its Vitamin D recommendation to 400 IU daily for all kids from ages 1 to 18. However, the official recommended Vitamin D requirement remains at 200 IU for adults aged 19 to 50. This level is low, compared to our neighbor north of the border. Canadians are recommended to take 1000 IU of daily Vitamin D supplements during fall and winter. This recommendation was made by the Canadian Cancer Society in 2007, after reviewing strong evidence about the anti-cancer properties of Vitamin D.

The Bottom Line

Studies suggested that Vitamin D deficiency is a highly prevalent condition, present in approximately 30% to 50% of the general population. Some people may have low levels of Vitamin D – especially those who wear sunscreen all the time or stay indoors often. Vitamin D not only aids calcium absorption, it also demonstrates a strong association with lowered cancer risk. And now, it may even be suggested as an immune-booster!

Food, unfortunately, is not a good source of Vitamin D. Therefore, we recommend Vitamin D supplements – particularly D3 supplements. In addition, it is wise to start including more foods that contain Vitamin D, like milk, fatty fish, egg yolks, and fortified food products like yogurt and breakfast cereals.


flu, vitamin c, vitamin d, zinc


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