If you’re over 60, there’s a good chance a pill organizer sits on your kitchen counter. About 76% of adults 60 and older take at least one dietary supplement, and more than half take two or more, according to the Centers for Disease Control and Prevention’s National Center for Health Statistics.
After multivitamins, vitamin D and omega-3 products like fish oil are the most common supplements Americans take, an earlier NCHS report found. Add glucosamine for creaky knees, and you’ve got the supposed good guys of the supplement aisle.
Now scientists are asking an uncomfortable question: Could some of those pills be hurting the very brain you’re trying to protect? The Washington Post laid out the latest research recently, and it’s worth a hard look.
Before you dump your pill bottles in the trash, understand what this research is and isn’t. Most of the red flags come from studies that spot patterns rather than prove cause and effect. And some findings contradict others.
But here’s what should bother anyone paying for this stuff: The Food and Drug Administration doesn’t approve supplements for safety before they hit store shelves.
In other words, nobody made these companies prove their pills protect your brain. Let alone that they don’t hurt it.
1. Fish oil: A billion-dollar habit with a brain problem
Fish oil is a more-than-$1-billion-a-year business in this country, according to Keck Medicine of USC. A big reason is the hope that the omega-3 fatty acids (essential polyunsaturated fats the body can’t produce on its own) in fish oil will help keep us mentally sharp.
USC researchers just ran about the toughest test of that hope you could design. They recruited 365 people ages 55 to 80 who rarely ate fish and faced a higher-than-average risk of Alzheimer’s.
Each was randomly assigned either a placebo or 2,000 milligrams a day of DHA, one of the key omega-3s in fish oil.
The pills worked, in one sense. After six months, DHA levels in the fluid surrounding participants’ brains were up an average of 17%. The omega-3s got exactly where they were supposed to go.
They just didn’t do anything once they arrived. After two years, the fish oil group scored no better on memory and thinking tests than the placebo group. Brain scans showed no protection against shrinkage of the hippocampus, a region that’s critical for memory.
Dr. Hussein Yassine, director of the USC Center for Personalized Brain Health and the study’s lead investigator, said fish oil supplements “do not appear to protect brain health.”
If you read our piece on why heavily advertised memory supplements don’t work, that won’t surprise you. But wasting money is one thing. Two other studies raise the question of harm.
This spring, researchers analyzed records from the Alzheimer’s Disease Neuroimaging Initiative, a long-running project that tracks memory and brain scans in older adults. They compared 273 people taking omega-3 supplements with 546 similar people who weren’t.
Over roughly five years, the supplement users declined faster on three standard tests of memory and thinking.
That’s a red flag, not proof. The study was observational, so it spotted a pattern without testing the pills directly. And critics noted that an earlier analysis of the same database had linked omega-3 use to a lower risk of Alzheimer’s.
The second warning is narrower. A Medical University of South Carolina study found that EPA, another major omega-3 in fish oil, seemed to hamper the brain’s repair process after repeated mild head injuries in mice.
The team saw a similar weakening in human brain blood-vessel cells in the lab. But lead investigator Onder Albayram said people shouldn’t read the work as a reason to stop taking fish oil.
That study didn’t look at falls. Still, I’d keep it in mind if you’re unsteady on your feet. Falls are the most common cause of traumatic brain injuries, and they send older adults to the emergency room about 4.5 million times a year, according to the CDC.
If that describes you, a few cheap home upgrades for aging in place are a smarter buy than another bottle of capsules.
2. Glucosamine: A joint pill with a brain question mark
We covered this recently, but it belongs on this list. Glucosamine is a go-to for achy joints, and seniors take it widely.
University of Florida researchers had artificial intelligence sift through UF Health patient records from 2012 through 2024. Among people with mild cognitive impairment, glucosamine users were 25% more likely to progress to dementia.
Among patients who already had dementia, those taking glucosamine faced a 25% higher risk of dying.
Glucosamine can cross from the bloodstream into the brain. The researchers believe it may feed a sugar-tagging process that’s already running in overdrive in Alzheimer’s brains.
Senior author Ramon Sun warned that many people with dementia take an over-the-counter supplement that “could be making their disease progression worse.”
The team stresses that it’s an association, not proof, and that a human clinical trial is needed. Notably, glucosamine wasn’t tied to extra deaths among people with mild cognitive impairment, suggesting the concern is greatest once dementia sets in.
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3. Vitamin D: The scariest finding is also the shakiest
Vitamin D has a well-established job in helping your body absorb calcium and keep bones strong. So when you hear it might be linked to dementia, it’s natural to sit up straight.
That alarm traces largely to a 2022 study from researchers in Taiwan. It found that dementia-free older adults who took vitamin D3 for more than 146 days a year were 1.8 times as likely to be diagnosed with dementia.
Among people who already had dementia, long-term users faced more than double the risk of death.
Sounds terrifying. But other scientists, including researchers at Oregon State University’s Linus Pauling Institute, pushed back hard.
They argued the Taiwanese records actually tracked calcitriol, a prescription drug used for people with kidney or parathyroid problems. That’s not the vitamin D you grab at the drugstore, and those patients tend to have other health problems to begin with.
Meanwhile, a stronger study points the other way. In a Finnish trial published in 2025, nearly 2,500 older adults took a placebo or 1,600 or 3,200 international units (IU) of vitamin D3 daily for up to five years.
Vitamin D made no difference in dementia rates at either dose. One caveat: Most participants weren’t short on vitamin D to begin with.
And in August, a small Emory University study of 54 people with sleep and memory problems linked doses of 5,000 IU a day or more to better scores on a cognitive screening test.
Even there, senior author Victoria Pak told Newsweek it’s too early to recommend high doses.
So what’s the real vitamin D risk? Taking too much. The National Institutes of Health sets the daily upper limit for adults at 4,000 IU, counting food and supplements together.
High doses can also clash with medications. According to the NIH’s consumer fact sheet, they may make some cholesterol-lowering statins less effective. Combined with thiazide water pills, vitamin D could push blood calcium too high.
As for who should take extra, the Endocrine Society suggests healthy adults under 75 stick to the standard recommended amount. For people 75 and older, it suggests more, because vitamin D may lower their risk of death.
What to do if these pills are in your cabinet
First, don’t quit anything your doctor told you to take. Some people have a genuine vitamin D deficiency, and some take omega-3s on medical advice. Those are conversations for your doctor, not a headline.
Second, if you or someone you love has memory problems, bring every supplement bottle to the next appointment. Ask specifically about glucosamine. Do the same for any fish oil or high-dose vitamin D you’re taking on your own.
Third, do the math. Say your supplement routine runs $30 a month. That’s $360 a year and $3,600 over a decade. If the best research says a pill isn’t protecting your brain, that money can go toward things that do.
What does? When U.S. News surveyed dozens of health experts, they found that what actually keeps you sharp after 60 wasn’t in a bottle. Regular movement and real food topped the list, with good sleep right behind.
And if you want omega-3s, eat them. The USC researchers suspect omega-3s may work better as part of a Mediterranean-style diet than in a capsule. Here are some foods high in healthy omega-3 fatty acids.
Finally, keep some perspective. Recently, we reported research suggesting omega-3 and vitamin D supplements might slightly slow biological aging. Supplement science flip-flops constantly. That’s exactly why you shouldn’t pay for promises.
The bottom line
The supplement industry sells certainty in a bottle. The science can’t back that up.
Nobody has proven these three pills are wrecking aging brains. But nobody has proven they’re protecting them, either. And right now, you’re the one paying for the experiment.
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