How obesity can hide—and accelerate—Alzheimer’s warning signs

The connection between obesity and Alzheimer’s isn’t new.

We’ve previously reported research showing how carrying extra weight can make the brain more vulnerable to Alzheimer’s, with changes in brain tissue and blood flow.

Other research has linked obesity to brain changes that resemble those seen in Alzheimer’s.

Now, researchers have followed that connection over five years—and uncovered a reason its warning signs could be underestimated.

Quick Answer

Obesity was linked to faster increases in Alzheimer’s-related blood markers and brain amyloid over five years. Initial blood results could look deceptively reassuring, possibly because greater blood volume diluted the markers. Repeated testing revealed the faster progression, reinforcing healthy weight as a brain-health priority.

What repeated blood tests revealed about obesity and Alzheimer’s

Researchers at Washington University School of Medicine in St. Louis analyzed five years of blood samples and brain scans from 407 adults enrolled in the Alzheimer’s Disease Neuroimaging Initiative.

The participants included people with normal cognition, mild cognitive impairment and Alzheimer’s dementia. The study, published in Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, examined how obesity related to changes in blood markers and brain amyloid over time.

Blood testing measured proteins that provide clues about Alzheimer’s-related pathology and nerve-cell injury. PET scans tracked amyloid plaques, a hallmark of Alzheimer’s.

At the beginning, higher body mass index was associated with lower blood-marker levels and less amyloid on scans.

That could have looked reassuring. But the repeated measurements over the years told a different story.

Why the first blood results could be misleading

The researchers believe greater blood volume in people with obesity could dilute the proteins measured by blood tests, making their concentrations appear lower.

“In fact, by relying on the baseline measurements, you could be fooled into thinking that the people with obesity had a lower pathology of Alzheimer’s disease,” says lead author Dr. Soheil Mohammadi.

This proposed dilution effect applies to the blood measurements. It doesn’t explain the initially lower amyloid readings on brain scans.

The distinction matters: a lower starting measurement and a slower rate of progression are two different things. Following the same people over time allowed researchers to see the trajectory.

And that trajectory was more concerning in participants with obesity.

Alzheimer’s-related markers rose faster with obesity

Over the follow-up period, participants with obesity experienced:

• A 29 to 95 percent faster rise in reported pTau217-related blood measurements. This marker helps identify Alzheimer’s-related pathology.
• A 24 percent faster rise in neurofilament light chain, or NfL. This protein is released when nerve cells are injured.
• A 3.7 percent faster increase in amyloid accumulation, measured by PET scans.

These percentages describe how quickly the measurements increased compared with those in participants without obesity. They don’t mean someone’s risk of developing Alzheimer’s rose by 95 percent.

Nevertheless, the findings show obesity was associated with faster progression of measurable Alzheimer’s-related changes.

Blood tests were particularly revealing: they captured obesity’s influence more sensitively than the PET scans. That strengthens the case for examining changes over time rather than relying solely on an initial result.

What the findings mean for your brain health

This study tracked biological changes, rather than proving that obesity caused faster memory loss. It also didn’t test whether losing weight reversed those changes.

But it adds urgency to treating healthy weight as a brain-health priority.

The 2024 Lancet Commission identified 14 potentially modifiable dementia risk factors, including midlife obesity, physical inactivity, diabetes and high blood pressure. Together, addressing these factors could potentially prevent or delay approximately 45 percent of dementia cases worldwide. That is a population estimate, rather than a guaranteed reduction in any individual’s risk.

You don’t have to overhaul everything at once. Start with a routine you can repeat:

• Make movement a daily appointment. A short walk is one practical starting point. Physical activity supports weight management and may help maintain aspects of thinking and memory.
• Build meals around nourishing foods. Vegetables, whole grains, protein sources and fish can form the foundation of a balanced eating pattern.
• Pay attention to blood pressure and blood sugar. Managing these conditions belongs in a brain-health plan alongside weight management.
• Aim for a healthy weight while protecting strength. Especially as you get older, weight management should account for muscle and adequate nutrition.

These are lifestyle changes, but I feel supplementing should be part of the conversation.

For starters, in a randomized trial of adults with overweight or obesity, participants following a weight-loss diet who also took omega-3 supplements experienced significantly greater reductions in abdominal fat than those following the diet alone.

The study was small and lasted 12 weeks, but it gives omega-3s a practical connection to the weight-management side of brain health. But of course, they also have a well-researched connection to supporting brain health…

Fish provide EPA and DHA, the primary omega-3 fats that support brain health, and research has associated regular fish consumption with better cognitive function and slower cognitive decline with age. But supplementing omega-3s may be important for this reason…

A few years ago, a clinical trial found that omega-3s have a hard time reaching the brain, except in participants taking a higher amount. So unless you’re eating fish daily, it’s hard to get the dosage they found to be helpful.

Supplementing krill oil has benefits over fish oil — including less stomach upset — and it takes less krill oil to raise blood levels of DHA because the body absorbs it more easily.

If you take blood thinners, though, talk to your physician before supplementing.

Remember, modifiable risk factors put you in the driver’s seat.

Sources:

Effects of obesity on plasma biomarker and amyloid PET trajectories in Alzheimer’s disease — Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring

Blood Test Shows Obesity Speeds Alzheimer’s Development — Radiological Society of North America

Blood tests reveal obesity rapidly accelerates Alzheimer’s progression — ScienceDaily

Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission — The Lancet

Cognitive Health and Older Adults — National Institute on Aging

What Do We Know About Diet and Prevention of Alzheimer’s Disease? — National Institute on Aging

The effect of omega-3 fatty acid supplementation on weight loss and cognitive function in overweight or obese individuals on weight-loss diet — Nutrición Hospitalaria

FAQ: How might obesity affect Alzheimer’s?