Alzheimer’s disease: Obesity may cause similar brain degeneration in older adults

According to Dr. Filip Morys, a postdoctoral researcher at The Neuro (Montreal Neurological Institute-Hospital) of McGill University and the first author of this study, obesity has negative effects on the brain, mostly in terms of neurodegeneration.

“It has been shown that obesity itself, but also related comorbidities, such as type 2 diabetes, hypertension, or dyslipidemia, might lead to neuronal loss,” Dr. Morys told Medical News Today.

“Obesity (is) much more than just sort of a number on a scale or some physical appearance — it’s a multi-complex, multi-system disease with broad effects,” explained Dr. Scott Kaiser, a geriatrician and Director of Geriatric Cognitive Health for the Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, CA.

“Somewhat recently, we’ve come to understand the direct impacts of obesity on our central nervous system, including our brain health,” Dr. Kaiser continued. “There are many mechanisms underlying this potential relationship. There’s the possibility of increased inflammation (and) oxidative stress — all of this driving a concept that I think about a lot in geriatrics called ‘inflamma-aging’. And impacts in terms of hormonal regulation, glucose metabolism, (and) insulin resistance. So a complex physiologic cascade of ways that being obese can directly impact the brain and brain function and brain cells.”

Dr. Karen D. Sullivan, a board certified neuropsychologist and creator of I CARE FOR YOUR BRAIN, told MNT that obesity — specifically increased body mass, high body fat percentage, and waist-to-hip ratio — are related to cognitive impairment in older adults and a risk factor for Alzheimer’s disease.

“A confound in previous data was the known metabolic changes that often, but not always, accompany obesity like diabetes, high blood pressure, and lipid disorders,” Dr. Sullivan said. “These metabolic changes result in cerebrovascular changes and neurodegeneration in specific parts of the brain that mimic the pattern of Alzheimer’s disease and all have been linked to an increase in Alzheimer’s disease-related brain pathology.”

Dr. Morys said this study was prompted by a previous study in which they saw that obesity-related neurodegeneration patterns were visually similar to the ones in Alzheimer’s disease:

“It was known previously that obesity is a risk factor for Alzheimer’s disease, but we wanted to directly compare brain atrophy patterns in both, which is what we did in this new study.”

In this study, Dr. Morys and his team compared patterns of gray matter atrophy — or loss of brain cells — in patients with obesity or Alzheimer’s disease. Using a sample of more than 1,300 individuals, they compared patients with Alzheimer’s disease to healthy controls and obese (otherwise healthy) individuals with lean individuals.

Upon analysis, scientists found that both obesity and Alzheimer’s disease affected the loss of grey matter brain cells — also known as cortical thinning — in similar ways. For example, researchers found cortical thinning in both the right temporoparietal cortex and left prefrontal cortex were similar in both groups.

Based on these findings, researchers believe losing weight could potentially slow cognitive decline and lower a person’s risk for Alzheimer’s disease.

“At this point, our study suggests that obesity prevention, weight loss, but also decreasing other metabolic risk factors related to obesity, such as type 2 diabetes or hypertension, might reduce the risk for Alzheimer’s disease and have beneficial effects on cognition.”

– Dr. Morys

After reviewing this study, Dr. Kaiser said while it is not an overall new concept, it substantiates a lot of our understanding of the critical connection between obesity and dementia risk and our understanding of modifiable risk factors.

“Obesity has been recognized as a modifiable risk factor for dementia and that’s been shown in population studies where they follow groups of people over time and see that people with obesity have a greater likelihood of developing dementia,” he explained.

“And in some studies, it’s on the order of a 1/3 higher rate of developing dementia than people with normal weight,” Dr. Kaiser added. “(There are) also animal studies that have been looking at the physiologic impacts of obesity on brain health. And so it’s all coming together to give an indication of a really important target, particularly in midlife, that could have significant effects for the decades ahead.”

Meanwhile, Dr. Sullivan said it is very clear that conditions like diabetes, high blood pressure, and lipid disorders, particularly when poorly controlled over long periods of time, contribute to neurodegeneration via poor oxygenation.

“We need to improve public health information about the negative impact of these conditions on brain health,” she continued. “They are incredibly responsive to lifestyle changes like diet, exercise, and reduced stress, especially in the earlier stages. We need more interventions that decrease these known metabolic risk factors to decrease the long-term risk of neurodegeneration and many subtypes of dementia.”