Many people to choose to down a multivitamin daily because getting those extra vitamins and minerals is believed to offer some kind of health benefit. However, to date there are no studies that show that long term use of multivitamins reduces risk of cancer, heart disease or any illness.
The promise of hope is a powerful motivator.
Even if there is strong evidence that multivitamins do nothing, many will be quick to dismiss the hard evidence and supplant it with traditional urban myth beliefs. Kind of like believing in fairies.
Interestingly there is a lot of hard evidence that shows eating healthy food and exercising regularly does decrease risk of heart disease, cancers, and even the common cold.
So, pop a pill that does nothing at all, except increase the amounts of vitamins and minerals in your urine, or eat healthy and exercise?
If the outcome that motivates you is reduced risk of illness over a lifetime, then eating healthy and exercising regularly will provide you with that, but a multivitamin will not provide any additional benefits.
A recent study once again shows multivitamins do nothing. 182,009 study subjects were followed for 11 years. 28, 851 study subjects died during the 11 year follow up period. There was no association with protection against cancer or cardiovascular diseases from use of multivitamins. (1)
There are definite exceptions for vitamin and mineral supplementation though.
We know that those living in northern latitudes, like us Canadians, will have reduced vitamin D levels as we progress into the winter season. I take 4000 IU/ day of vitamin D between October and May every year. I discussed my vitamin D intake with my physician.
Cancer Canada, Osteoporosis Canada, and Health Canada each have recommendations for vitamin D intake (click on links to find out).
As we age (generally above age 50-60) our GI may become less capable of absorbing some nutrients, like vitamin B12 and iron. You'll have to talk to your physician about this.
Woman who may become pregnant are encouraged to take a folate and iron supplement; definitely talk to a physician about this. Health Canada recommendations for prenatal nutrition.
Although athletes are a big target demographic to sell vitamin and mineral supplements to, eating healthy will provide all the nutritive needs of all athletes, generally a multivitamin will not help an athletes performance in any significant way (2, 3). There may be an exception with ultra endurance athletes, those running huge volumes day after day in extreme competition (4)
Some endurance athletes who train too much can reduce iron and iron stores; this occurs more with female athletes than male athletes, but both genders are affected, and those who run are affected more than those who don't run. Running can cause destruction of red blood cells by literally pounding the crap out of blood cells in the capillaries in the soles of your feet. Poor diet is also a contributor to what is referred to as "runners anemia" (microangiopathic hemolytic anemia).
This means some endurance athletes may need iron supplementation, but don't self prescribe, you need a doctor to do the appropriate blood work and dietary analyses in order to determine if you have anemia, what the cause is, and what course of treatment is best. Typical symptoms of runners anemia are fatigue and reduced performance that does not resolve with normal recovery periods.
It may be that many runners simply need to eat better and introduce more recovery into their exercise routines to prevent runners anemia.
(1) Multivitamin Use and the Risk of Mortality and Cancer Incidence
Multivitamins and athletes:
(2) The effect of 7 to 8 months of vitamin/mineral sup... [Int J Sport Nutr. 1992] - PubMed result
(3) Vitamin and mineral supplementation: effect on the... [Am J Clin Nutr. 1988] - PubMed result
(4) Multivitamin-mineral supplementation prevents lipi... [J Am Coll Nutr. 2007] - PubMed result