If you’re anything like me, taking vitamins was a part of your daily routine as a kid. At the time, I cared more about which flavor Flintstone chewable I got than the nutritional info behind the pill-sized likeness of Barney, Fred, or Wilma.

As I outgrew my beloved Flintstone chewables, I stopped taking a daily multivitamin in high school and college. But by the time I got to graduate school, I started to think more about my health and wondered if I should begin taking vitamin supplements again. As a PhD student in molecular biology, I have a habit of reading scientific studies in my spare time, so I started researching vitamin supplements to determine which ones were worth adding to my very tight budget.

I was surprised by what I found. Nutrition research can be a contentious field, with experts arguing about what’s really good for you. (Is coffee shaving years off your life or giving you a health boost?) But across the board, peer-reviewed, placebo-controlled scientific studies have consistently shown that vitamin supplements don’t prevent disease. And, in some cases, they might increase your risk of cardiovascular disease, cancer, and mortality.

Researchers, such as Regan Bailey at the National Institutes of Health, are unsure where Americans get the idea that they should take a daily multivitamin for better health. “It’s not from the doctors,” says Bailey, a nutritional epidemiologist in the NIH’s Office of Dietary Supplements. “The majority of scientific data available does not support the role of dietary supplements for improving health or preventing disease.”

And yet, half of Americans today regularly take vitamin supplements. Half. Besides the obvious role of marketing, why do so many of us allow ourselves to believe that vitamins are good for us with little proof? Have we become a society that believes we can correct an unhealthy lifestyle with a daily pill?

The Need for Vitamins

When I use the term vitamin here, I’m referring to chemical compounds with the word “vitamin” in front—such as vitamin A, which helps maintain good vision—but also things like calcium, potassium, and beta-carotene that serve similar functions in the body.

There’s no denying that prolonged deficiency of certain vitamins can lead to illness and disease. The real question, though, is whether vitamin supplements are necessary for healthy individuals.

If you eat a diet full of fruits, vegetables, and whole grains, there’s a good chance you already reach your suggested daily intake. And even if you eat a less-than-stellar diet, many types of processed foods are fortified with vitamins and minerals.

If you are taking a vitamin supplement in addition to eating well and consuming some fortified foods, you may be reaching vitamin levels much higher than the FDA and NIH recommend.

Multivitamins' Dark Side

To visualize the downside of overdosing on vitamins, let’s consider an analogy. Would you take a powerful antibiotic every day, just in case? That kind of attitude leads to the kind of antibiotic resistant bacteria we've seen recently.

So why do we think it's okay to have a just-in-case attitude when it comes to multivitamins? Certainly individuals at risk for a vitamin deficiency due to a poor diet or a preexisting medical condition should consider supplementing with a multivitamin to address that deficiency. But, if you're otherwise healthy and don't suspect a vitamin deficiency, the downsides of multivitamins easily outweigh the benefits.

Multivitamins often contain 100 percent (or more) of your recommended daily value of vitamin A, vitamin C, iron, and calcium. Unless you aren’t consuming any nutritional food at all, you simply don’t need these supplements.

Too Much of a Good Thing

So what happens when you start pumping too many vitamins and minerals into your body? Two meta-analyses of studies that collected data on the effects of multivitamin use in more than 400,000 patients found that individuals who took the daily supplement had an increased mortality rate Bjelakovic G, Nikolova D, Simonetti RG, et al. Antioxidant supplements for prevention of gastrointestinal cancers: a systematic review and meta-analysis. Lancet. 2004 Oct 2-8;364(9441):1219-28. Bjelakovic G, Nikolova D, Gluud LL, et al. Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis. JAMA. 2007 Feb 28;297(8):842-57. .

A separate 2007 study found that women who took multivitamin supplements (vitamin C, E, beta-carotene, selenium, and zinc) increased their risk of developing skin cancer Hercberg S, Ezzedine K, Guinot C, et al. Antioxidant supplementation increases the risk of skin cancers in women but not in men. The Journal of Nutrition. 2007 Sep;137(9):2098-105. .

While it appears that multivitamin supplements may have alarming effects, can single vitamin supplements still hold benefits for the body? The quick answer: For healthy adults, probably not.

Vitamin A
Vitamin A, which helps with vision and the immune system, is found in bright yellow and orange fruits and vegetables. All you need is one-quarter cup of sweet potatoes, a third of a cup of butternut squash, or half a medium-sized carrot to get your recommended daily value. It can also be found in dark leafy vegetables: a cup of kale or two cups of spinach will also give you your daily fix. Fortified sources, like most breakfast cereals, contain about 10 percent of the recommended daily value per serving.

Too much vitamin A, ingested through beta-carotene supplements, has been shown in two separate studies to increase the likelihood of developing lung cancer among smokers The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. The New England Journal of Medicine. 1994 Apr 14;330(15):1029-35. Omenn GS, Goodman GE, Thornquist MD, et al. Risk factors for lung cancer and for intervention effects in CARET, the Beta-Carotene and Retinol Efficacy Trial. Journal of the National Cancer Institute. 1996 Nov 6;88(21):1550-9. .
In one of these studies, the supplement increased the lung cancer risk by as much as 28 percent—so significant that it prompted the researchers to end the study early.

Vitamin E
Vitamin E, a great antioxidant, can be found in wheat germ, dark leafy vegetables, various nuts and seeds, and vegetable oils. A serving of typical cereal will give you nearly half your daily recommended value of vitamin E.

Like vitamin A, elevated levels of vitamin E can seriously impact your health. A study that aimed to look at the supplement's role in preventing cancer or cardiovascular disease found that excessive amounts of vitamin E increased patients' risk of heart failure Lonn E, Bosch J, Yusuf S, et al. Effects of long-term vitamin E supplementation on cardiovascular events and cancer: a randomized controlled trial. JAMA. 2005 Mar 16;293(11):1338-47. . A separate study on more than 135,000 patients found that supplemental vitamin E correlated with increased mortality rates Miller ER, Pastor-Barriuso R, Dalal D, et al. Meta-analysis: high-dosage vitamin E supplementation may increase all-cause mortality. Annals of Internal Medicine. 2005 Jan 4;142(1):37-46. . The authors even went as far as to conclude that vitamin E supplementation should be avoided. Lastly, a 2011 study in over 35,000 men reported that excessive Vitamin E supplementation significantly increased the risk of prostate cancer Klein EA, Thompson IM Jr, Tangen CM, et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2011 Oct 12;306(14):1549-56. .

Calcium supplements are highly recommended to women to build stronger bones as they age. They’re so pervasive that you can find them in tasty chocolate and caramel chewables, in addition to the usual tablet form. Three cups of milk and two cups of yogurt or tofu get you up to your recommended daily value of calcium. Fortified sources (two cups of soy or almond milk and a serving of cereal) provide the same benefit.

Despite all of the talk of calcium building stronger bones, a study found that calcium supplements actually increase patients risk of hip fracture Bischoff-Ferrari HA, Dawson-Hughes B, Baron JA, et al. Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomized controlled trials. American Journal of Clinical Nutrition. 2007 Dec;86(6):1780-90. . Additionally, four separate studies found that patients who take calcium supplements were at a higher risk of death from cardiovascular disease Michaëlsson K, Melhus H, Warensjö Lemming E, et al. Long term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study. BMJ. 2013 Feb 12;346:f228. Xiao Q, Murphy RA, Houston DK, et al. Dietary and supplemental calcium intake and cardiovascular disease mortality: the National Institutes of Health-AARP diet and health study. JAMA Internal Medicine. 2013 Apr 22;173(8):639-46. Bolland MJ, Avenell A, Baron JA, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010 Jul 29;341:c3691. Li K, Kaaks R, Linseisen J, et al. Associations of dietary calcium intake and calcium supplementation with myocardial infarction and stroke risk and overall cardiovascular mortality in the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition study (EPIC-Heidelberg). Heart (British Cardiac Society). 2012 Jun;98(12):920-5 .

Not Your Nutritional Insurance Plan

It’s too easy to think of vitamins as a “nutritional insurance plan.” If so many people take them, they must do something good, or at least not be harming our bodies, right? Doctors are catching on to the research and starting to advise against vitamin supplementation.

With that being said, remember that I specifically researched the effects of vitamin supplementation on healthy adults, aged 25-35. Although I have yet to come across any studies that said children or seniors benefit from a daily multivitamin, I didn’t look at those age groups in depth.

Also, just like any drug, vitamins can and should be prescribed for special cases. If you’re pregnant, your obstetrician/gynecologist will likely advise you to supplement with folic acid. If your doctor suspects you have a vitamin deficiency due to poor diet or a particular physiological problem, he or she might also advise you to use a specific supplement.

But for the rest of us, I simply couldn't find any real benefits to taking vitamins, and more alarming, there appears to be the potential for significant health risks to taking too much of any vitamin supplement.

This article was originally produced as part of 75toGo, a project to publish research-intensive health and fitness stories for twentysomethings looking to create good practices and habits for the decades ahead.

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