Obesity induces thinning of the cerebral cortex, and the distribution of this neurodegeneration is very similar to that observed in people with Alzheimer’s disease, reveals a study published on January 31, 2023 in the Journal of Alzheimer’s disease. Given these results, the researchers conclude that obesity is clearly a risk factor for developing Alzheimer’s disease and that weight loss interventions could certainly reduce this risk.
Researchers from the Neuro (Montreal Neurological Institute-Hospital) at McGill University and the CERVO Research Center at Laval University arrived at these findings based on data from more than 1,300 adults over 50. (Alzheimer’s patients, healthy control individuals, obese and cognitively healthy people, and lean people) from UK Biobank.
A first comparison between the cerebral cortex of obese subjects and that of thin people revealed a thinning of this region of the brain in obese individuals of the same age and sex. “From the age of 17, we begin to lose cortex. Age is the number one cause of brain tissue loss. The second cause is obesity. All the studies carried out using databases show that obesity leads to a loss of tissue in the cortex of the brain”, specifies neurologist Alain Dagher, of The Neuro, who led the study published in the Journal of Alzheimer’s Disease.
In order to better characterize the atrophy of the cerebral cortex observed in obese people, the researchers compared the images obtained by magnetic resonance of the brain of obese individuals with those of the brain of patients suffering from Alzheimer’s. They then noted that the distribution of gray matter atrophy was very similar in the two groups of individuals. “The distribution of atrophy was the same, but the atrophy was not as intense in obese people because they had no cognitive problems at the time of the study,” says Dr.r Dagger.
In both groups, atrophy appeared more marked in the temporal, parietal and frontal lobes of the brain, which are the regions where the first signs of neurodegeneration and cortical thinning associated with Alzheimer’s disease usually appear. But according to the Dr Dagher, it is “a phenomenon that is diffuse throughout the brain”. “There are certain areas that are more vulnerable than others, but when you do an autopsy of a person with Alzheimer’s, you see signs of the disease all over the brain,” he says.
A precursor?
“This cortical atrophy related to [l’accumulation de graisse] could, in vulnerable individuals, precede the development of an accumulation of beta and tau amyloid proteins, which, in turn, leads to the expression of Alzheimer’s disease”, advance the authors in their article.
The Dr Dagher mentions in this regard a study conducted in Montreal in which we follow healthy people who are at high risk of developing Alzheimer’s because they have a relative with the disease: we have already noted a loss of tissue in these people’s brains, but at this stage, “there is no evidence that these people will develop the disease, although it is very likely”. “As we follow these people for several years, we can probably answer this question,” he says.
“When you look at the cognitive losses in thousands of people, there are subtle differences between obese people and thin people. Very subtle differences, which might not show up in everyday life, except that they are there, and you see them when you do extensive testing. We think it’s an early sign of what’s going to happen eventually — an early sign of brain tissue loss, which may not cause symptoms when you’re 55, but eventually will cause problems.” he adds.
“Like cigarettes and lung cancer”
“If this phenomenon of brain atrophy is already present in obese people in their 50s, or even between 50 and 75 years old, this does not mean that these people will necessarily develop Alzheimer’s,” notes Dr.r Dagger. But this demonstrates that it is a risk factor on which we can intervene, like cigarette smoking for lung cancer. »
Several studies have shown that obesity in adulthood predisposes to Alzheimer’s disease, and Dr Dagher and his colleagues sought to understand the mechanisms by which obesity could lead to brain damage.
In an article published last year in The Journal of Clinical Endocrinology & Metabolism, they pointed to the multiple metabolic consequences of obesity, namely type 2 diabetes, hypertension, dyslipidemia (including high levels of lipids), as well as systemic inflammation. “Adipose tissue releases pro-inflammatory cytokines, as well as inflammation-associated proteins that lead to low-grade systemic inflammation,” they point out.
“Obesity consistently and chronically causes small amounts of brain damage. Inflammation, lipid accumulation, insulin resistance and hypertension cause vascular damage in the brain. And little by little, this damage accumulates and is thought to be what leads to the atrophy of brain tissue. The accumulation of this damage ends up triggering the process of Alzheimer’s disease,” explains Dr.r Dagger.
“Proving that obesity is a risk factor for this very serious and common disease supports the importance of treating obesity in everyone. There are treatments for obesity. There are new treatments coming out this year, but the problem is they aren’t approved for obesity because governments don’t want to pay. There is still this idea that obesity is the fault of the person [atteinte]who would lack self-control,” says Dr.r Dagger.