Experts have long known that obesity in midlife is a major risk factor for developing dementia as we age.
Although it may be intriguing, carrying a lot of excess weight in old age, when you are over 65, has been shown to have a protective effect against brain diseases that weaken the mind.
The two contradictory facts represent what researchers have called the “obesity paradox,” which challenges the conventional wisdom that being obese is always detrimental to health.
An important study published in JAMA Neurology examined 2,798 people, 480 of whom were diagnosed with dementia over a period of five and a half years.
The findings revealed that while obesity in midlife was associated with a 40 percent increased risk of dementia, the researchers found that between ages 60 and 65, it was associated with a lower risk.
The obesity paradox debunks the belief that fat always equals poor health when in fact being obese could protect against dementia
The graph shows that obese people appear to have a survival advantage over normal and underweight people (courtesy of JAMA Neurology)
The underlying reason for the paradox is unclear.
Studies have repeatedly shown a link between obesity and a higher risk of dementia due to the inflammatory effects of a larger body on the blood vessels that supply the brain, so an inverse relationship is counterintuitive.
Obesity in midlife is recognized as an important risk factor for vascular dementia, particularly characterized by reduced blood flow to the brain. Obesity is a risk for high blood pressure, which can damage blood vessels throughout the body.
It can also increase plaque in the arteries, which causes blood to flow through the arteries more slowly.
One theory postulates that a protein produced by fat cells called adiponectin may reduce inflammation in the brain.
Chronic inflammation is closely linked to a variety of neurodegenerative disorders, including dementias and Parkinson’s.
However, Fat cells also produce proteins called cytokines, as well as hormones that send signals throughout the body that can trigger an excessive immune response.
Obesity rates have reached their highest levels ever recorded
The fighter cells are released as if the body were being attacked by a virus, causing the brain to swell and increasing the risk of neurodegenerative diseases such as Alzheimer’s.
Obesity between the ages of 35 and 65 can increase the risk of dementia in later life by about 30 percent.
Obesity rates in the U.S. are at their highest point on record, with 42 percent of American adults qualifying as obese. Scientists have attributed this to an unhealthy diet and sedentary behavior driven by smartphone and social media use.
A 2015 UK study published in the prestigious Lancet It followed two million people in their fifties for about nine years, during which time approximately 45,500 were diagnosed with dementia.
Researchers found that underweight people with a BMI less than 20 kg/m2 had a 34 percent higher risk of dementia compared to people with a healthy weight.
However, those with a BMI in the obese category (30 years or older) were associated with a 37 percent lower risk of dementia compared to the healthy weight group.
The above shows the prevalence of dementia (proportion of people who have dementia) by year from 2000 to 2016. It reveals a gradual decline in rates.
Rates of obesity and gradual obesity have been on an upward trend since the turn of the century, peaking at 42 percent of Americans rated as obese.
Even very obese people with a BMI over 40 had a 29 percent lower risk of dementia compared to those with a healthy weight.
The pattern held after two decades of monitoring and adjustments for other factors that could influence the results.
The results baffled scientists. However, some say that one explanation may be due to the fact that people with obesity are more likely to see their doctor frequently for health problems that can contribute to dementia, such as high cholesterol and high blood pressure, and receive treatment for them.
Scientists have also highlighted that while obesity rates are steadily increasing, dementia rates appear to have decreased. Although many fear that a constantly aging population could have the opposite effect.
Some warn that the notion of obesity paradox could discourage doctors from discussing the risks of obesity to older patients.
Dr. Judith M. Kronschnabl, MA, researcher at the Munich Center for the Economics of Aging at the Max Planck Institute for Social Law and Social Policy in Germany, saying: ‘It has been suggested that higher weight or weight gain in old age may be beneficial in maintaining cognitive performance (but) we found no evidence of this.
He added: “Consequently, such an erroneous belief should not contribute to doctors’ reluctance to advise” obese or overweight patients to reduce excess body weight.
Until middle age, people should aim for a BMI of 20 to 25.