AHA News: Obesity Harms Brain Health Throughout Life – Yet Scientists Don’t Know Why

Thursday, Jan 13, 2022 (American Heart Association News) — Anyone who gains even a few pounds knows that it can slow down your speed. Over time, if those pounds turn fat, they can do serious damage, putting you at risk for a wide range of diseases.

But too much weight on the body can also harm the brain.

Research shows that obesity affects brain health from childhood to adulthood, affecting everything from executive function skills — the complex ability to initiate, plan, and carry out tasks — to dramatically increasing the risk of dementia. By middle age, the consequences of being overweight are significant. Several studies have shown that middle-aged adults with a body mass index (BMI) of 30 or higher, which is considered obese, are more likely to develop dementia than their healthy-weight peers.

However, researchers are still exploring how and why excess weight harms the brain, and whether the higher dementia risk is cumulative over a lifetime or if obesity affects the body differently at different stages of life.

It’s also possible that cognitive challenges come first, contributing to poor eating behaviors that start in childhood, said Alexis Wood, assistant professor of pediatric nutrition at the Children’s Nutrition Research Center at Baylor College of Medicine in Houston. The center is operated in partnership with the USDA Agricultural Research Service.

“There is strong and substantial evidence spanning the whole of childhood, from infancy to adolescence, that shows that higher weight status is associated with lower cognitive performance, particularly in the area of ​​executive function,” she said. “Why this is the subject of so much discussion.”

With obesity rates steadily rising in the United States, it is also a matter of great concern.

According to the Centers for Disease Control and Prevention, more than 42% of adults qualified as obese in 2018 — and nearly 45% were between the ages of 40 and 59. Among children and adolescents, obesity rates have increased with age: more than 13% of children under five years of age; 20% of those aged 6-11 and 21% of those aged 12-19.

And the pandemic hasn’t helped slow those stats.

The CDC said in September 2021 that the rate at which BMI increased nearly doubled during the pandemic compared to the period before it. The largest jumps were seen in children aged 6 to 11 who were overweight before the epidemic.

Some studies trace the beginnings of the relationship between diet, weight, and brain health all the way to the womb. In early childhood, there is already an association between excess weight and a child’s ability to control and direct behavior; incorporation of new information; plan; And it solves problems, Wood said. It is not clear which one comes first.

For example, a study published in the American Journal of Epidemiology found that children with higher verbal and executive skills in preschool were less likely to be overweight later in childhood. Other research shows that young children who are overweight or obese are less able to control impulses than those who are at a healthy weight.

“If the challenges of cognitive function come first, the prevailing thinking is that this regulates how children interact with their environment,” Wood said. “They may not be very good at regulating food intake to balance their energy needs. They may eat when they are not hungry, when they see something appetizing like a cupcake. Decreased cognitive function in this area changes eating behavior and makes you vulnerable to poor eating behaviors.”

However, if weight problems arise before the cognitive changes, it may be that excess fat increases inflammation. Over time, she said, this can lead to “changes in the connectivity, structure and function of the brain”.

One theory is that it’s not just excess weight that causes the problem, but the conditions and diseases associated with obesity that collectively contribute to poor brain health.

“People who are obese are more likely to develop type 2 diabetes, high blood pressure, and high cholesterol,” said Kristin Yaffe, MD, professor and vice chair of psychiatry, neuroscience, and epidemiology at the Weill Institute for Neurosciences in San Francisco. “It may be the set of cardiovascular risk factors associated with obesity that we know can have a detrimental effect on brain aging, whether that’s contributing to the development of Alzheimer’s disease or vascular dementia or some kind of combination of the two.”

Another possibility, Yaffe said, is that hormones secreted by fat cells, such as leptin, play a role. Leptin helps regulate hunger. However, people with too many fat cells produce so high levels of leptin that the body becomes insensitive to it, resulting in a cycle in which the person continues to eat because they never feel full.

Yaffe’s research published in the journals Gerontology: Medical Science showed that in older women of healthy weight, leptin levels were associated with a lower risk of dementia or cognitive decline. However, this protection disappeared in obese women.

It could be that obese people may be less active and more likely to develop other diseases that cause higher levels of inflammation, which “has a significant role in precipitating or exacerbating Alzheimer’s disease and vascular dementia,” Yaffe said.

While being overweight, especially in middle age, increases the risk of dementia, the opposite does not appear to be true: A large, long-term, federally funded study of a weight-loss intervention found no associated cognitive benefit.

“Frankly, we don’t know why that is,” said Mark Espeland, author of that long-term study published in the Journal of the American Geriatrics Association. It randomly divided middle-aged and older adults with type 2 diabetes who were classified as overweight or obese into two groups, one participating in an intensive weight loss program while the other did not. After 10 years, there was no difference in cognitive performance between the two groups.

It’s possible that no brain health benefit was observed because all study participants had type 2 diabetes, “which can disrupt brain function,” Espeland, MD, professor of gerontology and geriatrics at Wake Forest School of Medicine in Winston-Salem, said. North Carolina. “Diabetes is a disease that accelerates aging.”

Whether or not losing weight can prevent cognitive impairment, Espeland said, there are many reasons to strive to maintain a healthy weight.

“It’s fairly clear that obesity in middle age is bad for the brain and the rest of the body as well,” he said. “Preventing this from happening is very important.”

American Heart Association news covers heart and brain health. Not all opinions expressed in this story reflect the official position of the American Heart Association. Copyright is owned or operated by the American Heart Association, Inc. , All rights reserved. If you have questions or comments about this story, please email editor@heart.org.

By Laura Williamson

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