Could they harm the aging brain?

You reach into your pantry for a bottle of vitamin D. Then get some fish oil capsules from the fridge. Gulp! What’s a little fish burp for a healthier brain, right? But then you see the headline: Studies link vitamin D, fish oil and glucosamine to cognitive decline in older adults. Say what?

Doctors tout the benefits of vitamin D for strong bones, fish oil for a healthy heart and glucosamine for joint health. Omega-3 fatty acids found in fish oil have also been recommended for keeping the brain—the fattiest organ in the body—in top shape.

Did the team of trusty sidekicks just pull a 180?

Before you clear out your medicine cabinet, pause to consider the facts. David Madigan, a professor at Northeastern University’s Khoury College of Computer Sciences, and Carmen Sceppa, dean of its Bouvé College of Health Sciences, share their insights along with other experts.

Who needs supplements—and does the answer change with age?

“It’s always best to get the nutrients from foods,” Sceppa said. They provide a balanced mix of nutrients.

However, supplements can be a godsend for vegans and people with conditions that interfere with nutrient absorption, Sceppa explained.

Besides, salmon or canned sardines—a source of omega-3s—are an acquired taste. And while vitamin D is produced by the body, sunshine is a required factor—a tall order during a Boston winter. Past data from the National Institutes of Health (NIH), a federal research agency, found nearly 1 in 4 Americans had inadequate or deficient levels of vitamin D.

Age throws another curveball.

The brain’s metabolism changes over time, which affects how it handles nutrients. Still, plasticity keeps it in balance, Sceppa noted.

That is, until it doesn’t.

Sceppa explained that glitches in glucose metabolism can lead to the formation of amyloid plaques—protein clumps associated with Alzheimer’s disease. In some cases, excess supplements might contribute to the burden.

However, “the response is going to vary dramatically from person to person,” she said.

What can we make of observational studies?

When asked how much people can take away from theories about the harm these supplements might cause, Madigan didn’t mince words.

“Not much,” he said.

Randomized trials sit atop the evidence ladder. Scientists assign one group to take the supplement and another to take a placebo, making it easier to separate cause from coincidence.

In fact, VITAL, one such large-scale randomized trial on supplements and brain health, launched in 2009 and tracked 3,400 older adults. It found that neither vitamin D nor fish oil helped or harmed cognition, said Christopher Weber, senior director of global scientific initiatives at the Alzheimer’s Association, a nonprofit organization that funds research and provides support to those affected by the disease.

Observational research, on the other hand, simply looks at what people already do. Still, repeated findings across independent studies can become persuasive.

After all, that’s how the tobacco-cancer link was established, Madigan pointed out.

One-off supplement studies based on questionnaires are another story. Recall can be shaky, follow-up incomplete and cognitive changes difficult to measure.

Differences between the people within groups turn the uncertainty up a notch.

“The people who take fish oil … are probably not like the people who don’t take fish oil,” Madigan said.

Fish oil users may rarely eat fish, while those who take glucosamine often have osteoarthritis, Jaime Gahche, an epidemiologist at the NIH Office of Dietary Supplements, and her colleagues told Northeastern Global News. Those differences may affect cognitive health independently of the supplements.

How did the sunshine vitamin wind up in the hot seat?

Unlike vitamin C and other water-soluble vitamins the body can flush out, fat-soluble vitamin D settles into body tissues, Sceppa said.

She suggested that extra vitamin D might affect age-related metabolic shifts in a way that worsens plaque buildup.

The tendency to linger matters even more given that supplement strengths are all over the map.

One bottle may provide 1,000 international units per dose, while another packs in 5,000, Sceppa said. Throw in a multivitamin, and the daily total climbs even higher.

The upper intake limit for adults is 4,000 international units (100 micrograms) per day, Gahche and her team noted. So that 5,000-unit whopper already exceeds the ceiling.

Excess levels can also cause toxicity and interact with certain medications, Gahche added.

The verdict: Get your levels checked and watch the label.

What should people make of claims bashing fish oil?

As Gahche and her colleagues said, previous research showed a possible link between high-dose omega-3 supplements and atrial fibrillation, an irregular heartbeat associated with cognitive impairment.

Other observational studies have linked fish and omega-3 consumption to lower risks of cognitive decline and long-term supplement use to a 64% lower risk of Alzheimer’s.

Randomized trials haven’t found fish oil to be harmful for healthy older adults. Some show benefit for people with mild cognitive impairment, Gahche said.

The verdict: Omega-3 levels can be measured in the blood—so get yours checked and go from there.

How does glucosamine fit into the picture?

Glucosamine leads to the production of glycans—chains of sugar molecules that can build up, possibly making amyloid plaque worse and speeding up Alzheimer’s progression, Sceppa said.

Gahche and her team pointed out that glucosamine also “has potential safety considerations, including interactions with warfarin,” a blood-thinning medication.

The verdict: Tread carefully and check with your doctor.

What comes next, and what are the safest choices for brain health now?

According to Sceppa, a well-controlled intervention study—a broader category that includes randomized trials—would go a long way in settling the debate.

Until then, “homeostasis is key—so everything in moderation,” said Sharyn Rossi, referring to maintaining balance and not relying too much on external fixes. Rossi serves as senior director of neuroscience programs at BrightFocus Foundation, a nonprofit that funds research on Alzheimer’s disease and vision loss.

People with a known deficiency who feel better on a supplement can keep taking it in consultation with a doctor, she said.

In the end, no single vitamin or supplement has been proven to prevent or cure Alzheimer’s, Weber added. A balanced Mediterranean diet or MIND plan, a plant-based eating pattern developed to support brain health, remains the safest bet.

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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This story is republished courtesy of Northeastern Global News news.northeastern.edu.