Obesity in middle age is associated with an increased risk of dementia later in life, according to a study of more than 1 million women in the United Kingdom.
Those who were obese in their mid-50s had 21% greater risk of being diagnosed with dementia 15 or more years later, compared with women who had a healthy weight, a team of British and international researchers found.
The study adds to the “ever-expanding body of data that says what you do with yourself in midlife — and really even earlier — affects your risk for dementia as you age,” said Keith Fargo, director of scientific programs and outreach at the Alzheimer’s Association in Chicago. He was not part of the research.
For the study, the researchers followed about 1 out of every 4 women born in the United Kingdom between 1935 and 1950, more than 1.1 million overall. Their average age at the start of the study was 56. None had dementia.
At the outset, researchers calculated each woman’s body mass index (BMI), an estimate of body fat based on height and weight. They also asked about their diet and exercise. The women were followed for an average 18 years.
During that time, about 2.1% of obese women were diagnosed with dementia, compared to 1.6% of normal-weight women, the researchers found.
The study was published online Dec. 18 in the journal Neurology.
A lot of factors associated with obesity are bad for the brain, said Dr. Gayatri Devi, a neurologist and psychiatrist who specializes in memory disorders at Northwell Health in New York City.
These include high cholesterol, elevated levels of inflammation and increased stroke risk, said Devi, who was not involved with the study. Obese people tend to suffer poor sleep due to sleep apnea, and their brains struggle to get enough oxygen to function properly.
“You’re essentially beating your brain up when you’re obese, because your brain requires a lot of oxygen and a lot of nutrients to function day-to-day and maintain structural integrity,” he said. “Anything that challenges the body’s ability to maintain the proper function and structure of the brain is going to increase your risk for developing cognitive decline as you age.”
The researchers also looked to see if physical inactivity or an inadequate low-calorie diet were linked to dementia. They found no significant associations.
Low calorie intake and inactivity were associated with higher dementia risk during the first 10 years of the study, but the link weakened in subsequent years until it became insignificant, the study found.
“Other studies have shown that people become inactive and lose weight up to a decade before they are diagnosed with dementia,” lead researcher Sarah Floud, of the University of Oxford, said in a journal news release. “The short-term links between dementia, inactivity and low calorie intake are likely to be the result of the earliest signs of the disease, before symptoms start to show.”
But Fargo said he doesn’t put much stock into those findings, given that the study was relatively short and the fact that diet and exercise are so closely linked with obesity.
“If you have obesity at 56, chances are your diet and physical activity pattern hasn’t been all that great for potentially decades at that point,” he said. “I think it’s a little difficult to disentangle the obesity story and the physical activity/diet story, especially given that they only measured physical activity and diet one time, right at the intake into the study. No one really knows what was happening with these individuals’ diet and physical activity levels in that intervening 15 to 20 years.”
It’s also impossible to tell from this study whether losing weight, eating right and exercising in middle age will reduce your later dementia risk, Fargo said. Ongoing clinical trials are expected to shed light on that question.
Devi, however, said she is “absolutely” convinced that an obese person who loses weight in midlife improves his or her chances of avoiding dementia.
“I think there is never not a good time to improve general physical and cardiovascular health, improve brain health and reduce risk for Alzheimer’s,” Devi said.