One of the more common questions I get as a physician, and as a proponent of science-based medicine, regards whether or not it is helpful to take a multivitamin/mineral supplement (MVM) routinely for general health. Part of the reason this question is so common is because there has been a great deal of marketing trying to convince the public that this is a good idea.
In the US alone the vitamin and supplement industry was worth $36.1 billion in 2017. The industry also continues to grow and is expected to reach $278 billion worldwide by 2024. About half of Americans take vitamins regularly. This is perhaps the most iconic example of health marketing getting ahead of the science.
Vitamins, by definition, are necessary for health – they are substances that the body needs to carry out its biochemical functions, but cannot manufacture itself from other substances. You have to eat vitamins to get them. Minerals refer to trace minerals that also need to be consumed, since they are elements and cannot be manufactured. Since the discovery of specific vitamins and minerals, what they do, the diseases that result from their deficiency, and which foods contain them, the standard recommendation has been to get enough vitamins from food. This means having a varied diet with plenty of fruits and vegetables. This is still unequivocally the best advice.
Specific individuals or populations, however, may be insufficient or deficient in specific vitamins or have a greater need for a specific vitamin, and in such cases supplementation may be necessary. There have even been programs of fortification – adding specific supplements (like vitamin D to milk) to increase levels in the general population. Why, then, don’t we just fortify the drinking water with multivitamins to reduce the incidence of all vitamin deficiencies? (You might argue that, to a degree, we do, given the popularity of vitamin water and other fortified food products.) Would the expense and risk of such a program yield worthwhile health benefits?
Multivitamin use and vascular disease
The question of routine vitamin and mineral supplementation (meaning, in the general population, without a specific indication) is a difficult one to answer. Researchers would have to look at very large numbers of subjects over years, evaluating many possible supplements, diet, and a host of possible health outcomes. We could also look at subpopulations (sex, race, age, socioeconomic status, duration of supplementation, etc.) further multiplying the number of possible questions to be researched.
A recently published meta-analysis looking at MVM use in vascular disease takes a huge bite out of this massive set of questions. The researchers looked at: “Eighteen studies with 2,019,862 participants and 18,363,326 person-years of follow-up were included in the analysis.” Two million participants is a pretty powerful study. Here is what they found:
Overall, there was no association between MVM supplementation and CVD mortality (relative risk [RR], 1.00; 95% confidence interval [CI], 0.97–1.04), CHD mortality (RR, 1.02; 95% CI, 0.92–1.13), stroke mortality (RR, 0.95; 95% CI, 0.82–1.09), or stroke incidence (RR, 0.98; 95% CI, 0.91–1.05). There was no association between MVM supplements and CVD or CHD mortality in prespecified subgroups categorized by mean follow-up period, mean age, period of MVM use, sex, type of population, exclusion of patients with history of CHD, and adjustment for diet, adjustment for smoking, adjustment for physical activity, and study site.
CVD is cardiovascular disease, while CHD is coronary heart disease. Incidence is simply the number of people who develop the condition, while mortality is the number who die from it. So MVM use was not associated with any decrease in vascular mortality, or with stroke incidence. There was a slight decrease in CHD incidence, but this did not remain significant when they did a “pooled subgroup analysis of randomized controlled trials”.
The authors conclude:
Our meta-analysis of clinical trials and prospective cohort studies demonstrates that MVM supplementation does not improve cardiovascular outcomes in the general population.
About three months ago I wrote about another meta-analysis of vitamin use that came to the same conclusion. This review also looked at specific vitamins and looked at all-cause mortality as an outcome. This review found:
- Multivitamins, vitamins D, C, A, B6, E, calcium, β-carotene, zinc, iron, magnesium, and selenium had no benefit or harm for vascular disease or all-cause mortality.
- Folic acid and B-complex (Folic acid, B6 and B12) reduced stroke risk.
- Antioxidants and niacin increased all-cause mortality.
The data showing a reduced stroke risk, however, had problems. Specifically this finding was driven by a large study in China which does not fortify foods with folic acid so the population may be generally deficient, and therefore these results may not translate to other countries. This new meta-analysis shows that multivitamins (which include folic acid) were not associated with a reduction in stroke incidence or mortality.
What’s the harm?
In a 2015 survey 90% of the public thought it was a good idea to take a multivitamin. (In the same survey 80% of the public also said that taking a multivitamin does not replace a good diet.) This shows that the marketing has worked, despite the evidence. We can now say with a high degree of confidence that there is essentially no health benefit to routine supplementation. (I always have to emphasize that this does not include pregnant women or other special populations – consult your doctor.)
What most physicians practice is better termed targeted supplementation. We check vitamin levels and then make dietary advice or prescribe specific doses of supplements to address specific deficiencies, and follow up.
Many people, however, think of vitamin supplementation as “insurance”. Sure, have a healthful diet, eat your fruits and vegetable, but just in case a multivitamin can’t hurt. But everything in medicine should be viewed from the perspective of risk vs benefit. Spending collectively billions of dollars on unnecessary supplements is an opportunity cost that should not be ignored. In extreme cases I have seen patients who cannot afford needed prescriptions because they are spending hundreds of dollars a month on unneeded supplements.
There is also the well-known “false sense of security” factor. People may think they can get away with a less-than-ideal diet because they take MVM as insurance – but we know that vitamins do not compensate for a poor diet. They may even neglect other aspects of health care partly because of the false assurance of taking supplements.
There is also the small risk of toxicity from oversupplementing. This is not as rare as you might think. There is also the possibility of more subtle direct negative effects, suggested in the previous study showing increased all-cause mortality from taking anti-oxidants.
So the hype (as opposed to the science) surrounding vitamin supplements and supporting a massive industry likely provide no health benefit may cause some harm, can cause a false sense of security, and diverts resources and attention from other effective interventions. None of this implies that vitamins are not necessary for health, they are, but rather that in developed nations vitamin deficiency is not a problem for the general population.
I also seem to conclude articles on vitamins and supplements with the same nugget of advice, because that advice is still true and has not changed over decades of scientific research – eat your fruits and vegetables.