Will Extra Pounds Protect You Against Alzheimer’s Disease?

Martha Snyder Taggart, BrightFocus Editor, Science Communications
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A BrightFocus Health and Science News Brief

In recent days, dozens of articles have been written about new research on body weight and Alzheimer’s risk.  In both media and science circles, jaws are dropping over the study just published in Lancet Diabetes & Endocrinology suggesting that weight gain—even to the point of obesity—might protect against, rather than increase the risk, of Alzheimer’s.

For the moment, at least, the study’s findings challenge earlier assumptions and evidence, about the link between obesity and Alzheimer’s risk.

A research team led by Nawab Qizilbash, PhD, of Oxon Epidemiology and the London School of Hygiene and Tropical Medicine, analyzed two decades’ worth of medical records on nearly 2 million UK residents who had a median age of 55 years at baseline. The results showed that  obese men and women actually had a lower risk of Alzheimer’s disease than those who were normal weight. Perhaps as important, those who remained underweight had an increased risk of Alzheimer’s.

Their analysis showed that underweight people had a 39% greater risk of dementia compared with being a healthy weight, and those who were overweight had an 18% reduction in dementia risk, which climbed to 24%—a one-fourth reduction in risk—for people who were obese.

"It is a surprise," Qizilbash said in a BBC News interview, and he acknowledged the findings would cause controversy.

"The controversial side is the observation that overweight and obese people have a lower risk of dementia than people with a normal, healthy body mass index,” he said. "That's contrary to most if not all studies that have been done, but if you collect them all together our study overwhelms them in terms of size and precision."

Reasons for Skepticism—and Why Confirmation Is Needed

In the world of science, there are differing levels of “proof.” Retrospective cohort studies like this, which analyze data that has already been collected on large numbers of people, lead to broad findings that may or not be accepted. However, what is widely agreed is that a study of this type is not capable of offering proof, nor of pinpointing causative factors, behind its findings.

“Clearly, further research is needed to understand this fully, "Simon Ridley, PhD, of Alzheimer's Research UK, said in a  BBC news analysis.

To be taken as “gospel,” the same findings would have to be repeated in a controlled study that would be designed in advance to rule out “confounding factors,” meaning any differences besides body weight that might differ between individuals who developed Alzheimer’s versus those who did not.

As an example, “many people with dementia tend to lose a lot of weight before the symptoms of cognition loss appear,” mentioned Diane Bovenkamp, PhD, BrightFocus scientific program officer.

Thus, “one factor to rule out might be whether being thin is associated as a consequence, rather than a possible cause, of Alzheimer’s disease,” she suggested. Among the $5.9 million in Alzheimer’s Disease Research grants BrightFocus has awarded in 2015, some funds will go towards investigating the relationship between weight loss and dementia.

Beyond simply determining cause and effect of weight gain and loss, studies like that are needed to probe into possible ways in which body weight interacts with Alzheimer’s disease. From a basic science standpoint, the possible contributions of diet and metabolism have not been fully explored or articulated. 

For example, as one of the initial stabs at explaining the surprising results from Qizilbash et al, some people are speculating that vitamin deficiencies believed to contribute to Alzheimer’s—possibly, in vitamins D and E, for example—may be less common in people who weigh more. But this, too, remains unproven. Investigations into nutritional deficiencies and benefits in Alzheimer’s disease represent a field that is growing, but is still relatively small and easily dismissed.

The Take Home

One thing is certain—no one should regard these latest findings as license to go on a binge-eating spree. All expert commentators have made that point.

"You can't walk away and think it's OK to be overweight or obese,” says Dr. Qizilbash himself. “Even if there is a protective effect, you may not live long enough to get the benefits.” That’s because adding inches to your waistline can greatly increase your risk of heart disease, stroke, diabetes, some cancers, and other diseases, some of which overshadow Alzheimer’s as leading causes of death.

"To understand the association between body mass index and late-onset dementia should sober us as to the complexity of identifying risk and protective factors for dementia,” Deborah Gustafson, PhD, of SUNY Downstate Medical Center, NY, commented to the BBC. Her own research focuses on adipose [fatty] tissue hormones in relationship to dementia and cognition, and she’s involved in several European research collaborations surrounding diet, physiology, and brain health.

As complex as they may be, the dietary, nutritional and metabolic factors in Alzheimer’s disease also may prove to be a boon—another strategic intervention point, along with disease modifying therapies—if people can be convinced to make dietary and lifestyle changes. And if weight gain ultimately is shown to be protective, there’s a good chance the added calories will be even more helpful if they are nutritious and provide proven benefits to the brain and overall health.

Glossary Terms

  • Dementia is group of symptoms that are associated with a decline in thinking, reasoning, and/or remembering. Alzheimer's disease is the most common form of dementia.