Abdominal obesity and the risk of young-onset dementia in women: a nationwide cohort study.

Background and objectives: The association between obesity and young-onset dementia (YOD, defined as dementia diagnosed before age 65) is established, but the specific impact of abdominal obesity in women remains unclear. Abdominal obesity, driven by excess visceral fat, may increase dementia risk through metabolic and vascular pathways. We investigated the association between abdominal obesity and YOD risk in women using a large nationwide cohort.

Methods: We analyzed 964,536 Korean women aged 40-60 years who underwent national health checkups in 2009. General obesity was defined by body mass index (BMI), and abdominal obesity was categorized by waist circumference (WC) into < 75 cm, 76-84 cm, 85-94 cm, and ≥ 95 cm. YOD was identified using ICD-10 codes and dementia medication prescriptions. Hazard ratios (HRs) for YOD were estimated using multivariable Cox proportional hazard models adjusted for lifestyle and clinical factors.

Results: Over a median follow-up of 8.2 years, YOD incidence increased progressively with higher WC. Women with WC ≥ 95 cm had a 55% increased risk of YOD (HR 1.55; 95% CI 1.34-1.79) compared to those with WC < 75 cm. The association was particularly strong for vascular dementia (VD), with HR 1.83 (95% CI 1.30-2.57). By contrast, BMI showed a U-shaped relationship, with the lowest YOD risk observed in women with normal BMI (18.5-22.9 kg/m²), and significantly elevated risks in both underweight (BMI < 18.5 kg/m²; HR 1.39, 95% CI 1.13-1.71) and morbidly obese women (BMI ≥ 30 kg/m²; HR 1.26, 95% CI 1.10-1.45).

Discussion: Abdominal obesity is a significant, independent risk factor for YOD in women, particularly for VD. These findings underscore the importance of addressing abdominal obesity in middle-aged women to reduce dementia risk.