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Could obesity reduce levels of gray matter in the brain? Ed Reschke/Getty Images
  • A new study from the University of South Australia finds that some types of obesity lead to a reduction in the brain’s gray matter and investigates its association with risk of dementia and stroke.
  • With obesity becoming more and more common, the link between body fat and cognitive health raises an alarm.
  • Researchers report that people with unfavorable or neutral types of obesity were at highest risk of reduction in the brain’s gray matter.

A new study from researchers at the University of South Australia explores a link between body fat and a higher risk of dementia or stroke.

The study finds a link between some types of body fat and a reduction in gray matter, a part of the brain that contains most of its neurons and is critical to cognitive function.

Lead author Anwar Mulugeta, Ph.D., researcher at the Australian Centre for Precision Health at the University of South Australia, explains,

“We found that people with higher levels of obesity, especially those with metabolically unfavorable and neutral adiposity subtypes, had much lower levels of gray brain matter, indicating that these people may have compromised brain function, which needed further investigation.”

The study appears in the journal Neurobiology of Aging.

“Gray matter,” Dr. Mulugeta told Medical News Today, “is an essential component of the brain that is rich in neuronal cell bodies, glial cells, and capillaries. As it is located in different regions of the brain, the gray matter has multiple roles, including learning, memory, cognitive function, attention, and muscle control.”

As such, Dr. Christina E. Wierenga, who was not involved in the study, told MNT that “age-related cognitive decline and dementia are often associated with reduced gray matter, called atrophy.”

Dr. Wierenga added: “For instance, Alzheimer’s disease dementia is associated specifically with hippocampal atrophy, or reduced gray matter in the hippocampus, which extends to other regions as the disease progresses. So, in some regards, [the] quantity of gray matter may signify cognitive health.”

Obesity is on the rise worldwide. According to the World Health Organization (WHO), nearly 2 billion adults currently have overweight, and 650 million of them have obesity.

The problem extends to children as well, with nearly 40 million children younger than 5 years old and over 340 million young people aged 15–19 years also considered to have overweight or obesity.

The WHO reports that there is an association between overweight or obesity and a range of health problems.

These problems include cardiovascular disease — particularly heart disease and stroke — diabetes, musculoskeletal disorders, such as osteoarthritis, and some cancers.

“In this study,” Dr. Mulugeta says, “we investigated the causal relationships of individuals within three metabolically different obesity types — unfavorable, neutral, and favorable — to establish whether specific weight groups were more at risk than others.”

The lead author of the study explained the three types of obesity, “Individuals with a high genetic load for unfavorable adiposity are characterized by fat accumulation around the abdomen and internal organs, high cholesterol, and increased risk of type 2 diabetes and coronary heart disease.”

He went on to say: “Individuals with favorable adiposity have fat accumulation more around the hip and less on the internal organs, with a lower risk of type 2 diabetes and connective heart diseases. Individuals with neutral adiposity have no link with type 2 diabetes and connective heart diseases.”

“Even in a relatively normal weight individual,” says the study’s senior author Prof. Elina Hyppönen, “excess weight around the abdominal area may be a cause of concern.”

Prof. Hyppönen adds, “It is increasingly appreciated that obesity is a complex condition and that especially excess fat which is located around the internal organs [has] particularly harmful effects on health.”

As evidence of obesity’s complicated role in health, Dr. Wierenga cited the “obesity paradox.”

She explained that “obesity in midlife is associated with poor cognition and increased risk of cognitive decline, but […] increased [body mass index (BMI)] in late life [may be] associated with better cognition — perhaps due to the fact that decreased BMI in late life may reflect overall poorer health/nutrition.”

The researchers analyzed over 336,000 self-reported health records in the UK Biobank, documenting the experiences of nearly 28,000 individuals. They then linked these records to hospital and death records to track associations with cases of dementia and with strokes.

The study found that for every extra 3 kilograms of body weight in a person of average height, the amount of gray matter decreased by 0.3%.

“In practice,” says Prof. Hyppönen, “our findings very much support the need to look at the type of obesity when assessing the type of likely health impact.”

Dr. Mulugeta notes:

“However, we did not find conclusive evidence to link a specific obesity subtype with dementia or stroke. Instead, our study suggests the possible role of inflammation and metabolic abnormalities and how they can contribute to obesity and gray matter volume reduction.”