4 Questions About How Obesity Affects Dementia Risk
In women, obesity during midlife may cause dementia later in life, according to results of a new study.1
The study team—led by Sarah Floud, PhD, who is a senior epidemiologist in the Cancer Epidemiology Unit in the Nuffield Department of Population Health at the University of Oxford in the United Kingdom—evaluated whether midlife obesity is a cause of dementia and whether risk factors such as diet or physical inactivity were causes or consequences of the gradual onset of dementia.
To better understand the connection between obesity and dementia, Neurology Consultant reached out to Dr Floud.
NEURO CON: Can you tell us more about your study and how it came about?
Sarah Floud: The data for this paper comes from the Million Women Study, a large prospective study of UK women.2 We recruited 1.3 million women aged 56, on average, and asked them to report their height, weight, physical activity levels and diet. We then followed them for nearly 20 years to see who had a diagnosis of dementia in their hospital records.
We knew from other studies that people who go on to develop dementia start to reduce their levels of physical activity and lose weight at least a decade before a diagnosis. Therefore, we knew that we needed to have followed the women for much longer than a decade, in order to separate out the short-term associations, which may just be a consequence of the gradual onset of dementia affecting behavior, from the long-term associations, which are more likely to reflect causes of the disease. The results from previous studies have been contradictory, which appears to be due to the varying lengths of follow-up in the different studies.
All of our analyses took into account other factors that might affect the women’s risk of dementia (for example, their education level and whether they smoked or drank alcohol).
NEURO CON: How do body mass index (BMI), physical inactivity, and poor diet in midlife affect dementia risk among women later in life?
SF: Obesity in midlife (ie, in women’s 50s and early 60s) was associated with a higher risk of dementia in late life (women were aged 75 years, on average, when they were first recorded as having dementia). Women who were obese had, on average, a 21% greater risk of dementia compared with women with desirable BMI (20-25 kg/m2). Lack of exercise and low caloric intake in midlife were not associated with dementia after 10 or more years of follow-up (in the first 10 years of follow-up, any associations were the consequence of behavior changes due to early dementia).
NEURO CON: What do these findings mean for clinical practice and how dementia might be managed or prevented in the future?
SF: These findings suggest that interventions to encourage weight reduction in midlife may lead to lower incidence of dementia later. They also suggest that interventions aimed at increasing physical activity levels or changing dietary habits may not be effective for preventing dementia.
NEURO CON: What knowledge gaps still need to be filled regarding the risk factors for dementia?
SF: There is still much uncertainty about the causes of dementia. The insidious onset of the disease and its effect on reducing various activities, such as eating an adequate diet and being physically active, mean that we need to have large studies with long follow-up to obtain robust and unbiased information on the causes of dementia.
- Floud S, Simpson RF, Balkwill A, et al. Body mass index, diet, physical inactivity, and the incidence of dementia in 1 million UK women. Neurology. 2020;94(2):e123-e132. https://doi.org/10.1212/wnl.0000000000008779.
- The Million Women Study. University of Oxford. http://www.millionwomenstudy.org/introduction/. Accessed February 12, 2020.