Limited evidence of a threshold effect for increasing adiposity on risk of symptoms at midlife.

Objective: To assess the nature of relationships between increasing body mass index (BMI) and the prevalence of midlife symptoms in a population with high adiposity.

Methods: In the cross-sectional Study of Women's Health in Qatar, 841 participants aged 40 to 60 years were recruited from nine primary health centers in Doha. Face-to-face interviews collected demographic, menopause, and symptom information. BMI (kg/m 2 ) was categorized as healthy, overweight, or class I, II, or III obesity. Multivariate logistic regression models were used to examine aches/stiffness in joints, trouble sleeping, shortness of breath, urinary incontinence, and hot flashes with BMI categories. Restricted cubic splines (RCSs) were used to estimate relationships between continuous BMI and each symptom and to conduct formal tests of nonlinearity.

Results: Mean BMI was 34.3 kg/m 2 (SD, 6.0 kg/m 2 ). Women with class II and III obesity had higher odds of reporting aches/stiffness than women with a healthy BMI, and the odds of reporting urinary incontinence were three times higher among women with class III obesity (odds ratio, 3.08; 95% confidence interval, 1.17-8.14). Using restricted cubic spline models, a significant nonlinear association ( P = 0.002) was observed between aches/stiffness and BMI with an apparent threshold of 38 kg/m 2 . Linear relationships were observed with BMI for urinary incontinence ( P < 0.001 for linear trend) and shortness of breath ( P = 0.005 for linear trend). Trouble sleeping and hot flashes were not associated with BMI.

Conclusions: Even at very high levels of BMI, likelihood of urinary incontinence and shortness of breath increases with BMI. In contrast, likelihood of aches/stiffness has a nonlinear relationship with BMI, increasing to a threshold level.