“If you want to help support your immune system, crack open this bottle.”
– Vitamin Water Defence (Vitamin C+Zinc)

“The zinc helps to maintain immune system and function.”
-Centrum ProNutrients Immunity

” Vitamin A maintains resistance to infection”
-Swiss Natural Vitamin A Capsules

Many supplements on the market claim to support immune function. Does taking them make you less likely to get a cold, flu or another sinus infection? Actually, in clinical trials, people who take vitamin A or zinc – or other vitamins and minerals- almost never get fewer infections like colds or the flu than those who take placebos.

If there is lack of clinical evidence, how are these claims allowed?

Let’s blame Health Canada’s standards. The Natural Health Products Directorate allows immunity claims on supplements that contain even trivial amount of zinc or vitamin A.  This is because our immune systems need these nutritients to function. However Health Canada doesn’t require companies to showcase the clinical evidence relating to improvement in immune function from taking their products. This is how the wording ‘helps to maintain immune function’ is allowed. Consumers interpret this as providing better protection against colds and diseases when this claim really has to do with vitamin A and zinc being essential for immune function. Here is what scientists have found about some of the key nutrients that ‘support’ immunity.

Vitamin E

  • In three well-designed studies, people who took 15-74 IU of vitamin E (the daily value is 15 IU) as part of a multivitamin every day for an average of 15 months were no less likely to get a cold or the flu than similar people who took a placebo.
  • However in a study of 450 nursing home residents who were given 200 IU a day of vitamin E for one year had 20%  fewer colds than those who were given a placebo. Although this is only a modest effect, colds in older people are more of a serious problem than in younger people. In addition, our immune systems become more compromised by age, so perhaps supplementation has a more profound effect on already compromised immune systems vs more health immune systems.


  • Taking zinc did not prevent colds or other respiratory infection in five studies that gave 10-20 mg of zinc (daily value is 9 mg) alone or as part of a multivitamin to older adults every day for 1 year.
  • Zinc lozenges may be more likely to help. In some studies, sucking on at least 75 mg of zinc from lozenges every day at the first sign of a cold cut down it’s duration by up to two days.

Vitamin D

  • Since 2012, three trials in Western Europe and the United States have given 1,650 people either 1,000 IU to 6,800 IU of vitamin D (daily value is 200 IU) or a placebo every day for 18 months. In none of the studies did the vitamin D takers have fewer respiratory infections, or were their symptoms milder or shorter in duration.
  • Two large trials are now testing vitamin D on colds and flu, but so far the evidence is not convincing.

Vitamin A

  • Vitamin A supplementation has helped make measles vaccines more effective for children with vitamin A deficiencies in developing countries. However vitamin A deficiency is not a problem for adults in  the developed world.
  • Three trials had women and men taking a placebo or 1333 IU to 2000 IU (daily value is 3333 IU) of vitamin A a part of a multivitamin every day. Over the next 12-18 months, the people in both groups were equally as likely to get sick.

Vitamin C

  • In a large study, people received a placebo or the daily value (60 mg) of vitamin C as part of a multivitamin. However, after 15 months, those who were taking the multi got no fewer colds or respiratory infections.
  • What about large amounts? Large amounts of vitamin C does not prevent colds but it can shorten the duration if they’re taken every day before getting one. This is demonstrated in 24 trials on nearly 11,000 adults.

From the above research, there does not seem to be a significant impact towards preventing colds and illnesses with any of the mentioned supplements among otherwise healthy, well-nourished adults. Be critical of immunity claims on products, as what is regulated by Health Canada may be deceiving. What to do instead to prevent colds?

  • Keep your hands clean.
  • Get the flu shot.
  • Get enough sleep.
  • Try to stay upbeat.
  • Do what you can to minimize long- term stress.


J. Am. Geriatri. Soc. 55: 35, 2007.
BMJ 331: 324, 2005.
JAMA 288: 715, 2002.
Arch. Intern. Med. 159: 748, 1999.
Am. J. Clin. Nutr. 85: 837, 2007.

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