Obesity May Increase Alzheimer’s Disease Risk By Affecting Brain Structure and Blood Flow

Previous studies have identified obesity as a risk factor for the development of Alzheimer’s disease (1). Although widespread, obesity is a modifiable risk factor and an ideal prevention strategy for Alzheimer’s disease. Understanding how obesity impacts our brains and the risk for Alzheimer’s disease is critical to helping us tackle this age-associated neurodegenerative disease that is taking a greater toll globally every year.

How Does Obesity Act As a Risk Factor For Alzheimer’s?

We don’t know exactly how obesity is tied to Alzheimer’s disease, but researchers think that obesity is responsible for several mechanisms that lead to the disease, including inflammation of the nervous system and dysfunction of the protective blood-brain barrier. All these changes could contribute to developing the disease, while also accelerating the damage done to nervous tissue.

We also know that the timing of obesity seems to affect the severity and onset of the disease. For example, a review of studies on Alzheimer’s found that a higher Body Mass Index (BMI) during mid-life is linked to an increased risk for dementia, even more so than an increased BMI in older age.

Obesity’s Effects On Brain Structure and Circulation

Brain circulation is an important factor in the development of the changes that cause Alzheimer’s. Most patients in the early stages of the disease have reduced patterns of cerebral blood flow, while also experiencing a loss of white matter  — the tissue through which messages pass between different areas of neurons within the central nervous system.  The patterns of nervous system tissue loss seem to vary depending on the stage of the disease and the age of the individual (2,3).

Higher Obesity Is Linked to Deficient Brain Structure and Blood Flow

The structural changes in the brain have been considered to be tied to the effects of obesity on cerebral circulation. For these reasons, a group of researchers from the UK and Finland studied the effects of obesity on the structural components of the brain, as well as the effects on brain circulation across a group of Alzheimer’s patients during different stages of the disease. Their findings were recently published in The Journal of Alzheimer’s Disease Reports (4).

For the study, 172 Alzheimer’s disease patients were recruited and classified according to the severity of their cognitive impairment. The first group had patients with mild Alzheimer’s disease, the second group consisted of patients with mild cognitive impairment, and the last group would serve as a control group with cognitively healthy patients.

The authors then measured several parameters, such as BMI and waist circumference, to calculate obesity indices. Once these measurements were taken, participant’s brains were examined using special imaging techniques that help researchers visualize the state of brain components like gray matter volume, white matter integrity, and cerebral blood flow.

What they found was that participants with higher indices of obesity showed signs of reduced brain structure and diminished blood flow in the brain. In contrast, being overweight or obese seemed to confer some level of protection to the participants who were already suffering from the disease. This shows that obesity may have a detrimental effect on brain function. So, having a healthy weight and better nutrition could help preserve the brain’s structure and blood flow.

A joint author of the study, Dr. Matteo De Marco from the University of Sheffield's Neuroscience Institute, said:  "We found that maintaining a healthy weight could help preserve brain structure in people who are already experiencing mild Alzheimer's disease dementia. Unlike other diseases such as cardiovascular disease or diabetes, people don't often think about the importance of nutrition in relation to neurological conditions, but these findings show it can help to preserve brain structure."

It’s Never Too Early To Start Your Alzheimer’s Prevention Plan

So, preventative interventions that advocate for healthy behaviors across the lifespan but especially during middle-age should continue to be promoted to reduce the risk of developing Alzheimer’s disease in old age.

The lead author of the study Professor Annalena Venneri from the University of Sheffield's Neuroscience Institute and NIHR Sheffield Biomedical Research Centre said, "Prevention plays such an important role in the fight against the disease. It is important to stress this study does not show that obesity causes Alzheimer's, but what it does show is that being overweight is an additional burden on brain health and it may exacerbate the disease."

She added, "The diseases that cause dementia such as Alzheimer's and vascular dementia lurk in the background for many years, so waiting until your 60s to lose weight is too late. We need to start thinking about brain health and preventing these diseases much earlier. Educating children and adolescents about the burden being overweight has on multimorbidities including neurodegenerative diseases is vital." 

References:

1.  Alford S, Patel D, Perakakis N, Mantzoros CS. Obesity as a risk factor for Alzheimer's disease: weighing the evidence. Obes Rev. 2018;19(2):269-280. doi:10.1111/obr.12629
2.  Lowe CJ, Reichelt AC, Hall PA. The Prefrontal Cortex and Obesity: A Health Neuroscience Perspective. Trends Cogn Sci. 2019;23(4):349-361. doi:10.1016/j.tics.2019.01.005
3.  Willette AA, Kapogiannis D. Does the brain shrink as the waist expands?. Ageing Res Rev. 2015;20:86-97. doi:10.1016/j.arr.2014.03.007
4. Dake, Manmohi D. et al. ‘Obesity and Brain Vulnerability in Normal and Abnormal Aging: A Multimodal MRI Study’. Journal of Alzheimer's Disease Reports. 2021;65 – 77.