The science behind supplements doesn’t always match the reputation behind them.
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I get why supplements are popular: Taking a pill feels easier than addressing lifestyle factors, such as poor diet or sleep.
But in many cases, the claims behind supplements aren’t backed by strong data. And you can’t redeem an unbalanced diet by popping a pill to fill in the nutrient gaps.
As a doctor, I tend to be wary of most supplements without a medical reason. Supplements are not regulated by the Food and Drug Administration the way medications are, and putting anything into our bodies involves a risk-benefit calculation. While the risks of taking certain supplements are not absurdly high, don’t mistake them for zero. Run any new supplements by your physician to ensure you’re not at a higher risk of a bad outcome.
So what should you know about specific supplements? Here are nine popular ones I’ve discussed in previous columns, and what the science says about them.
1. Multivitamins
About one-third of Americans take multivitamins regularly. Many purchase the supplement because they think it can affect broad health outcomes — help them live longer, decrease cancer risk and reduce cardiovascular disease. Otherwise-healthy people also take it to fill gaps in their diets.
I wish it was that straightforward. Though there’s some encouraging data on the benefits of multivitamins for healthy adults, the supplement isn’t a cure-all: A study published last year in JAMA Network Open of nearly 400,000 adults who were followed for almost 30 years found that multivitamins did not confer any longevity benefit.
Taking a multivitamin daily is generally regarded as safe. But because there isn’t enough evidence of benefits for healthy adults, the U.S. Preventive Services Task Force does not recommend it.
My advice? Follow a healthy diet. This has been well established in multiple large studies to improve numerous health outcomes, from reversing coronary heart disease to reducing cancer risk.
2. Psyllium
Most supplements aren’t worth your money. But this one is.
Robust studies have consistently shown psyllium husk — or psyllium, for short — may lower our cholesterol, dampen glucose spikes, help us stay full longer, and even aid in treating constipation and diarrhea — all while serving our microbiome a sweet, sweet feast.
Psyllium comes from the mainly soluble fiber outer shell of the Plantago ovata plant. It’s the primary ingredient in many over-the-counter fiber supplements, but what sets psyllium apart from other fibers are two properties:
• It’s rich in arabinoxylan, a molecule that forms a gel when it contacts water, allowing psyllium to promote special reactions, including the conversion of cholesterol into bile acids, as it makes its way through the digestive tract.
• When psyllium reaches the colon, it becomes a prebiotic for your microbiome, spurring the production of beneficial metabolites such as short-chain fatty acids.
These properties result in numerous health benefits that are backed by decades of research.
3. Collagen
Supplementing with collagen has become increasingly popular in recent years, with brands claiming it can boost nail, skin and hair health. But there isn’t strong evidence behind these claims.
Collagen is a protein found in many parts of the body — in cartilage, bone, tendons and skin. It helps build a structural framework to preserve the skin’s integrity. But as we get old, we produce less collagen. This contributes to skin appearing less elastic — even saggy — and wrinkles forming more easily.
Though several studies on collagen supplementation point to increased elasticity and improvement in wrinkles in skin, the data is often muddied by confounding study design, lack of objective microscopic evidence or funding straight from the people selling the products.
4. Ashwagandha
Ashwagandha has become popular among high-profile celebrities and TikTok scrollers for many reasons — they claim it improves sleep, anxiety, memory and even muscle mass.
Those who use ashwagandha to help with sleep are probably availing themselves of its known sedating qualities (its Latin name, Withania somnifera, references this). But while ashwagandha may adequately induce sleep, it shouldn’t be viewed as a long-term solution. Before trying it, I’d recommend seeing your health care provider to understand what’s causing your sleep issues. There are many reasons for insomnia, such as depression and sleep apnea, for which ashwagandha is not the first choice of treatment.
5. Magnesium
The data on taking a magnesium supplement is underwhelming for some of the purported benefits popularized on social media, including taking magnesium for sleep and mood symptoms. There are a few clearer circumstances where magnesium supplementation could be warranted, such as for constipation, but it’s hard for a doctor like me to give magnesium supplementation an unconditional stamp of approval.
Although too much magnesium can be toxic to your body, taking low levels — less than 350 mg daily — probably won’t cause any harm unless you have kidney disease. But it may not do any good, either.
Here is an alternative I can gladly endorse: Eat more magnesium-rich foods. That way, you’ll get the boost of magnesium as well as the other natural benefits of these foods.
6. Iron
People with an iron deficiency often feel exhausted. If that sounds like you, you should ask your doctor about getting tested for iron-deficiency anemia.
Young children, people who have heavy menses or are pregnant, and older people should be particularly vigilant. A study published in the Annals of Internal Medicine in 2023 found that about 1 in 4 healthy adults, 70 and older, developed anemia within five years of enrolling in the study and that taking a low-dose daily aspirin increased that risk by 20%.
If you have iron-deficiency anemia, you should take an iron supplement. But here’s an interesting pro-tip I share with my patients: Don’t take it every day. A study found that taking an iron supplement every other day can optimize iron absorption — and may mitigate side effects such as nausea and constipation.
7. Greens powders
Greens powders, made with greens such as kale and algae, are hugely popular on social media. They’re also expensive. I appreciate that fresh vegetables are often not cheap, but once you’re dropping $50 to $100 on a month’s supply of powdered greens, maybe your money is better spent on interventions with proven benefit.
Many of these formulas are proprietary, meaning we don’t fully know what’s in them. What we do know is that they’re heavily processed: Greens powders are at the very least freeze-dried, powdered and often mixed with additives and sweeteners.
Ask yourself this: Does your greens powder taste good mixed in water? You probably couldn’t stomach fresh broccoli and water. So what was added to that powder to make it tolerable to you?
Eating fresh vegetables is always going to be more beneficial than taking greens powders.
8. Vitamin B12
Some people think that vitamin B12 can help with fatigue and boost energy levels. But there’s no proven benefit to taking vitamin B12 for fatigue unless you have a deficiency that causes anemia.
Start by asking your doctor for a simple set of blood tests for vitamin B12 and related biomarkers. Adults above age 65 and vegans are particularly at risk of a deficiency. If you’re deficient in the vitamin, you should take a supplement.
For everyone else looking for an energy boost, my advice is to talk to your physician about other ways to help with energy levels, including making lifestyle changes or getting tested to rule out potential medical issues such as thyroid disease.
9. Probiotics
Probiotics are a multibillion-dollar for-profit industry. But most people who take them are wasting their money.
I’ve seen wide-reaching promises about probiotics touted everywhere — in supermarkets, pharmacies, online and on television by “gut health experts,” including fellow physicians. Proponents claim probiotics can boost your microbiome — the organisms that live inside your gut — and help with digestive issues, immune function and even mental health.
But the marketing claims about over-the-counter probiotics largely do not match the evidence. As a gastroenterologist, I rarely advise my patients to start a probiotic — much to their surprise. They’re even more surprised when I tell them that’s part of the evidence-based guidelines: The American Gastroenterological Association does not recommend probiotics for most digestive conditions.
Instead, here’s what I do recommend: Eat a fiber-rich diet. This time-tested recommendation remains one of the strongest-studied ways to promote and preserve a healthy microbiome and improve your overall health.
• Trisha Pasricha is a physician and journalist and an instructor of medicine at Harvard Medical School.
