Wandering into any conversation about vitamins and other health supplements is wandering into a thicket of hyperbole and half-truths. We're here to cut through some of the bullshit.
The biggest fallacy we need to let go of is that all vitamins are good, and more vitamins is always better. Vitamins are potent chemicals packed in potent pills.
"That's a nutrient exerting a pretty powerful effect on your physiology," Dr. David Katz, founding director of the Yale Prevention Research Center tells me. "People need to recognise that anything that has a potential to go good has a potential to do harm."
At very high doses—from taking more than the recommended dose over time—vitamins can indeed become toxic, causing everything from upset stomachs to seizures, depending on the specific chemical. But even just unnecessary supplements can upset the biochemistry of your body. Katz likens the body to a construction site, where vitamins and minerals are the raw materials for building. Get a huge delivery of superfluous concrete, and, well, it's only going to be in the way.
So which supplements are worth bothering with? How do you know you're not just throwing money out the door when you grab a multivitamin off the shelf? Amidst the confusion, there are certain supplements where the scientific evidence for taking them is much stronger than others. And there are supplements where popular misconception far outweighs the scientific evidence.
Of course, science can contradict itself at times. (Does coffee cause cancer? Prevent cancer?) And confounding factors, (coffee drinkers are also more likely to smoke) can muddle the conclusions of poorly constructed health studies. The best studies randomly assign groups to one or the other. But even then, any one study can still be a statistical fluke. I combed through the medical literature to look for meta-analyses, which look at the conclusions of many studies—usually randomised, controlled trials if possible—to come to the most informed conclusion.
Disclaimer: The best vitamins and minerals to supplement your diet with of course vary individual to individual, based on your personal health. Naturally, don't let this be a substitute to a good conversation with your doctor.
The stuff worth taking
Zinc: for shortening colds
Forget vitamin C (more on that later), the real supplement you should be taking when you feel that ominous itch in your throat is zinc. A 2011 meta-review of 15 randomised, double-blind, placebo-controlled trials—basically the gold standard for trials—found that zinc shortens a cold when taken within the first 24 hours, when symptoms set in. The mineral interferes with the replication of rhinoviruses, which cause colds.
Vitamin D: for people who don't get enough sun
Unlike most other vitamins, our bodies can synthesise perfectly adequate amount of vitamin D all by itself—as long as we get enough sun. The ultraviolet radiation in sunlight helps our skin turn cholesterol into vitamin D. But most people who live in the wide swath of the north, where winters are long and days are short, don't get enough sun for sufficient levels of vitamin D.
The vitamin is essential for aiding the absorption of minerals like calcium, iron, magnesium, and phosphate. (That's why, for instance, you often get milk fortified with vitamin D.) A 2013 meta-analysis found that vitamin D decreases overall mortality in the long-term. Vitamin D supplements haven't been proven to prevent cancer or depression or any number of things it's often touted for, but most of us could benefit from a boost.
Vitamin B3 (niacin): for heart health
A 2009 meta-analysis found that niacin can be beneficial for heart health: It decreases levels of high-density lipoprotein cholesterol (the "bad" kind) and increases levels of low-density lipoprotein cholesterol (the "good" kind). For people who aren't already taking statins, getting a high dose of niacin from a supplement could help lower the risk of cardiovascular disease. Niacin is naturally found in a variety of foods, with highest concentrations usually in meat.
Probiotics: for after antibiotics
By now, you've heard that your gut is teeming with microbes, most of them actually good. Taking antibiotics is basically a scorched earth approach of killing bacteria, taking out the beneficial and harmless along with the bad. If you've ever had a diarrhoea after a course of antibiotics, then you know what microbial genocide feels like.
Probiotics, usually containing Lactobacillus, can help prevent that, according to a meta-analysis of 82 randomised, controlled trials. With the rise of the microbiome medicine, probiotics have now been touted for all sorts of problems. Those aren't proven yet, but their benefits after an antibiotic regimen are pretty clear.
Vitamin B12 for dementia among the elderly
As we get older, health problems like low stomach acidity can make it harder to absorb vitamin B12. Low levels of vitamin B12 are associated with cognitive decline, according to a 2012 meta-analysis, and a deficiency can cause a type of dementia. This type of dementia, which crucially is not Alzheimer's but presents similar symptoms, can be reversed by taking vitamin B12 supplements.
The overhyped stuff
Last year, the Annals of Internal Medicine published a splashy trio of studies about the inefficiency of supplements accompanied by one very sharply worded editorial titled "Enough Is Enough: Stop Wasting Money on Vitamin and Mineral Supplements." The title really says it all.
The three long-term studies found there was no measurable benefit of multivitamins for preventing heart health, cancer, or cognitive decline. A multivitamin isn't tailored to your particular diet or needs, so any effect it may have will be small.
If you're like me, you've probably had vitamin C foisted upon you by well-meaning friends and family at the hint of a cold. However, there is just no conclusive evidence that vitamin C prevents or mitigates colds in healthy people. A 2007 meta-analysis of 30 studies and a total of 11,350 participants, found that taking a mega-dose of vitamin C is not justified.
Nevertheless, the perception that vitamin C is good against colds has been hard to shake. (Hello, shelves of Airborne and Emergen-C.) The persistent myth can be traced all the back to the enormously popular 1970 book Vitamin C and the Common Cold by Linus Pauling, a Nobel-prize winning chemist who was right about one big thing (the nature of chemical bonds) and wrong about oh no many others. Pauling's advocacy has made vitamin C part of the popular misconception, but multiple large studies, as summarised it that meta-analysis, have shown it's just not the case.
Vitamin E is a good example of a vitamin where supplements might actually be oversupplementing us. One meta-analysis from 19 clinical trials found that vitamin E actually increased overall mortality at doses greater than 150 IU per day. Vitamin E supplements are often sold at 400 IU and up. At even higher doses above 1500 IU per day, vitamin E can prevent blood from clotting and counteract vitamin K.
How to choose
Supplements are meant to fill specific holes in your diet and lifestyle, and you have to identify them. Tools like InsideTracker, which tests your blood for various biomarkers, can tell you what you're deficient in, though many of its tests can be done at your doctor's office, too. Bottom line, sit down with your doctor or a dietitian.
It's also worth noting, the quality of supplement products varies greatly from brand to brand. Not only can the amount of active ingredient differ from the label, but adulterants can also be sneaked in. If you're wondering if your (expensive) brand is up to snuff, Consumer Labs regularly publishes tests comparing the quality of different brands. Pro tip: More expensive is not always better.
All right, this was all a lot to take in. But if you want more, the Office of Dietary Supplements at the National Institutes of Health is a great, if sometimes technical, resource. Now go forth, be healthy and informed.