Association of BMI, dementia fluctuates over time in women

Takeaway

• Relative to normal-weight peers, women with obesity had a 21% higher rate of dementia at 15 or more years of follow-up in this longitudinal study, but the association of BMI and dementia changed over time.

Why this matters

• Interventions for preventing and treating dementia are limited.
• In an editorial, May A. Beydoun, PhD, and Mika Kivimaki, FMedSci, write that the associations among weight status, related behaviors, and dementia are complex, and call for more long-term studies of the associations of these factors with different stages of dementia over time.

 Key results

• At mean 18-year follow-up, 2.7% cohort had experienced hospital admission with a dementia diagnosis code.
• Compared with normal-weight peers (BMI, 20-24.9 kg/m²), women with obesity (BMI, ≥30 kg/m²) had dementia risk that was:
  • Lower during years 5-9: rate ratio [RR], 0.79 (95% CI, 0.71-0.89);
  • Similar during years 10-14: RR, 1.04 (95% CI, 0.99-1.11); and
  • Higher during years ≥15: RR, 1.21 (95% CI, 1.16-1.26).
• Risk during years ≥15 driven by vascular dementia, dementia of unspecified type.
• Low BMI (<20 kg/m²), low caloric intake (lowest quintile), and inactivity (exercise rarely/never or less than once weekly) all predicted dementia during the first decade but not clearly thereafter.

Study design

• Prospective population-based cohort study of 1,136,846 UK women with a mean age at baseline of 56 years (Million Women Study).
• Main outcome: dementia.
• Funding: UK Medical Research Council; Cancer Research UK.

Limitations

• Baseline measures self-reported.
• Reliance on diagnosis codes.
• Milder dementia not captured.
• Residual and unmeasured confounding.