A new, long-term study finds that midlife obesity raises the risk of dementia in women. However, calorie intake and physical inactivity do not.
Sarah Floud, Ph.D., of the Nuffield Department of Population Health at the University of Oxford in the United Kingdom, is the lead author of the study.
As Floud and her colleagues explain in their paper, some previous studies have found an association between a low body mass index (BMI) and the likelihood of receiving a diagnosis of dementia within the next 5–10 years.
Other studies that lasted a decade or less have also linked poor diet and lack of exercise with the incidence of dementia.
However, all of the above may be the result of reverse causality, meaning that they may be consequences, rather than causes, of dementia. This situation could well be possible, explain the authors, because dementia typically affects cognition a decade before the person formally receives a diagnosis.
During this preclinical stage, the condition can slowly but gradually affect behavior, impair mental and physical activity, reduce the intake of food and calories, and cause weight loss.
Furthermore, explain the authors, some recent meta-analyses have pointed out that although in the short term, a low BMI may be associated with dementia as a result of reverse causality, over a longer period, obesity is positively associated with dementia.
Either way, prospective studies over longer periods are necessary to settle the matter of how BMI connects to dementia risk. Floud and her team set out to do exactly this.
Their findings appear in the journal Neurology.
Studying diet, inactivity, BMI, and dementia.
The team examined 1,136,846 women in the U.K. They had an average age of 56 years and were free of dementia at the start of the study, between 1996 and 2001.
The women gave information about their height, weight, calorie intake, and physical activity, and the researchers clinically followed them until 2017 through the National Health Service records. These records also noted any hospital admissions for dementia.
They classified women who exercised less than once a week as inactive and those who exercised at least once weekly as active.
Women who had obesity at the beginning of the study were 21% more likely to develop dementia than women who don’t.
More specifically, 2.2% of the women with obesity went on to develop dementia in the long term, compared with 1.7% of those with heathy BMI.