I present to you the top three responses my patients give me when I ask them why they are taking a multivitamin:
1) “Just to be on the safe side.”
2) “It can’t hurt.”
3) “I don’t know.”
If you are one of those people taking a multivitamin for these or other reasons, you have lots of company. About 1/3 of Americans take a multivitamin (which often includes a multimineral, too). When you read the vitamin manufacturers’ promises to “help support your immune system” or “help support your body’s energy,” who wouldn’t want to take one? After all, we all know we need a certain amount of vitamins and minerals from our diet to be healthy, and often our diets are not what they should be. But is a multivitamin actually a way to make up for a less than optimal diet?
Multivitamins have only been around since the 1940s. Before then, the term vitamin didn’t even exist. The first vitamin was identified in 1913, and to date 13 vitamins and 15 essential minerals have been identified. Vitamins are nutrients that our own bodies cannot produce, but we need in small amounts to survive. Until the advent of synthetic vitamins and minerals, people relied on food and sunshine for all their nutrients. For most people, this was quite sufficient.
It would seem logical that vitamins could only help your body, and certainly not harm it, since we already eat them in our food. Besides logic, there is evidence from observational that supports the idea that vitamins are beneficial. But before accepting this evidence as truth, it’s important to understand what an observational study is and why the results of these studies have been misinterpreted by many.
In observational studies, researcher do just that – they observe what people are doing and see what happens to their health. It’s a way of determining if there is a correlation between what the participant does (e.g., taking a multivitamin) and their health (e.g., getting cancer). The more definitive way to understand the effect of vitamins on health is with a randomized controlled trial. This determines causation. In these types of studies, half the people are given the vitamin and half are given a placebo, and none of the participants knows which she is getting. Once these trials were done with vitamins, it became clear that most had nothing beneficial to offer us, and some were even harmful.
Why the discrepancy between the randomized trials and the observational studies? It turns out that the people who take multivitamins, or specific vitamins, often take better care of themselves. They are less likely to drink heavily and more likely to eat well and exercise. The vitamin-takers probably fared better because of their other good health habits, not because they were taking a multivitamin.
One of the first studies that showed that a vitamin could actually be harmful is that of beta carotene, an antioxidant, and cancer. A randomized controlled trial was begun because observational studies showed a decreased risk of cancer in those who took beta carotene. This trial showed that beta carotene did not decrease risk of cancer. Even worse, participants who were smokers or exposed to asbestos actually had an increased risk of lung cancer if they were taking the beta carotene.
Another randomized controlled study in 2009 looked at the effect of the antioxidant vitamins C and E on healthy young men who exercised. All the participants exercised, but only half received the vitamins. The researchers found that those who exercised but did not take the vitamins had improved insulin sensitivity. That is, their bodies were better able to keep their blood sugar at a normal level. The men who took the supplements and exercised showed none of that improvement in insulin sensitivity.
While studies of people in developing countries have shown some clear benefits (particularly among children, pregnant women and those with HIV/AIDS), clinical trials in countries like the U.S., where severe nutritional deficiency is uncommon, have not. Among randomized controlled trials that have looked at vitamins as a means to reduce cancer risk, only one has shown benefit: taking high doses of calcium reduced the risk for colorectal polyps, which may be precancerous lesions. (But even this is not currently recommended by the medical establishment, perhaps because high dose calcium can cause kidney stones and might even be connected to cardiovascular disease.) The other studies which evaluated multivitamins, beta carotene, folate, selenium, and vitamins E, C, D, B6 and B12, did not find convincing evidence that they decrease one’s risk of cancer.
The story is the same for preventing heart disease. Randomized controlled trials showed no benefit for folate, beta carotene, vitamin B6, B12, C or E.
There are many possible explanations for why the studies of vitamins and minerals have come up empty. Maybe the dose wasn’t right, the combination of vitamins was wrong, or the vitamin was synthetic rather than ‘whole food.’ A more likely reason is that each vitamin, or even all vitamins, represents only a fraction of the nutrients in food. Did you know that thousands of phytochemicals have been isolated from plants? These nutrients are not critical for life, but they have been shown to have a myriad of health benefits. (If you are curious about the phytochemicals in various foods, go to phytochemicals.info.)
Although multivitamins haven’t been shown to improve health, certain vitamins are clearly beneficial in specific situations. Women who are pregnant need adequate folic acid and iron. Vitamin B12 supplementation is important for people on a vegan diet because they have no dietary source of B12. And that may be it. It is not even clear that vitamin D and calcium supplements belong on this list. A number of studies show they help decrease fracture risk for people with low calcium intake and/or low vitamin D levels. But there are quite a few large studies which show no benefit to the bones from taking them. (There is an increasing amount of evidence that points to an overall benefit from supplementing with vitamin D in people who are deficient, but I don’t think the evidence is definitive yet in its favor.)
The idea that we can isolate a single nutrient from food and expect it to improve our health is overly optimistic and clearly mistaken. Each whole food is chock full of nutrients balanced in a way that is invariably the most ideal for our bodies. It is unrealistic to think that nutrients which are synthesized in a laboratory and reduced to the size of a pill can be a substitute for healthy eating.
In the meantime, if you are healthy, don’t look to a multivitamin to help you get healthier or live longer. The majority of studies, thus far, indicate they don’t do you any good, and occasionally, they may actually be harmful. Take what you need, such as B12 if you’re vegan, or iron if you are iron-deficient, but don’t count on a multivitamin to put you on the “safe side.” There’s just no getting around the fact that a healthy diet is the best way to get the nutrients you need.