Data from: Body mass index, diet, physical inactivity and the incidence of dementia in one million UK women

Objective: To help determine whether mid-life obesity is a cause of
dementia, and whether low BMI, low caloric intake and physical inactivity
are causes or merely consequences of the gradual onset of dementia, we
recorded these factors early in a large 20-year prospective study and
related them to dementia detection rates separately during follow-up
periods 0-4, 5-9, 10-14 and 15+ years. Methods: 1,136,846 UK women, mean
age 56 (SD=5) years, were recruited in 1996-2001 and asked about height,
weight, caloric intake and inactivity. They were followed until 2017 by
electronic linkage to National Health Service records, detecting hospital
admissions with mention of dementia. Cox regression yielded adjusted rate
ratios (RRs) for first dementia detection during particular follow-up
periods. Results: 15 years after the baseline survey only 1% were lost to
follow-up and 89% remained alive with no detected dementia, of whom 18,695
had dementia detected later, at mean age 77 (SD=4) years. Dementia
detection during years 15+ was associated with baseline obesity (BMI 30+
versus 20-24 kg/m2: RR=1.21, 95% CI 1.16-1.26; p<0.0001), but not
clearly with low BMI, low caloric intake or inactivity at baseline. The
latter three factors were associated with dementia rates during the first
decade, but these associations weakened substantially over time,
approaching null after 15 years. Conclusions: Mid-life obesity may well be
a cause of dementia. In contrast, behavioural changes due to preclinical
disease could largely or wholly account for associations of low BMI, low
caloric intake and inactivity with dementia detection during the first
decade.