Sex-specific associations between midlife body mass index and later-life left atrial enlargement in the Hordaland health study

Background Increased body mass index (BMI) leads to blood volume increase and left atrial enlargement (LAE). It is not known whether BMI and BMI change in midlife predispose to LAE later in life in a sex-biased manner. Methods Data from 1051 women and 889 men aged 42 years (baseline), followed for 26 years in the Hordaland Health Study, were analysed. LAE was identified from LA volume/height 2 using sex-specific thresholds. Associations between baseline BMI and LAE at follow-up were explored in sex-specific Poisson regression analyses and reported as relative risk (RR) with 95% CIs. Results At baseline, overweight was less common in women than men while obesity prevalence did not differ. At follow-up, the LAE prevalence was similar (48% in women, 46% in men; p=0.47). Overweight was associated with a significantly higher risk of LAE in women than men, RR 1.45 (95% CI 1.27 to 1.65) and RR 1.26 (95% CI 1.09 to 1.46), respectively, risk difference 0.16 (95% CI 0.08 to 0.25). Obesity was associated with a high risk of LAE in both women and men, RR 1.48 (95% CI 1.14 to 1.92) and RR 1.41 (95% CI 1.05 to 1.90), risk difference 0.12 (−0.11 to 0.34). The relative excess risk due to interaction was 0.25 (95% CI 0.02 to 0.49), indicating a positive additive interaction between female sex and overweight. Conclusions Increased BMI in early midlife was more strongly associated with LAE later in life in women. These results point to a sex-biased vulnerability to overweight-induced LAE and highlight the importance of weight control in midlife, especially in women.