Associations between insomnia and body mass index among the general Norwegian adult population: The Tromsø Study 2015-2016.

Aims: Insufficient sleep and increasing body mass index (BMI) are two emerging, and often related, public health concerns. Limited attention has been given to how insomnia is associated with BMI, particularly in subarctic regions with extreme seasonal climate and daylight differences. We aimed to investigate the association between insomnia and BMI among community-dwelling residents of Tromsø, Norway stratified by sex. Methods: This cross-sectional study was based on data from the seventh survey of the Tromsø Study (Tromsø7). We included 15,364 participants aged 40-65 years, who had complete BMI measurements and insomnia questionnaires. Sex-stratified multiple linear regression analyses were conducted to assess the association between insomnia and BMI. Socioeconomic, lifestyle, health, and biological factors were included as covariates. Results: The overall prevalence of insomnia was 29.7%, with a higher prevalence among women (33.9%) compared with men (25.0%). The association between insomnia and BMI was statistically significant for both sexes. In the final multivariable model, compared with sex-specific non-insomniacs, insomniacs had on average 0.43 kg/m2 (95% confidence interval (CI) 0.21 to 0.64) higher BMI among men and 0.27 kg/m2 (95% CI 0.41 to 0.51) higher BMI among women. Conclusions: This study demonstrates a significant association between insomnia and BMI in both sexes within the Tromsø population and can be a basis for longitudinal and experimental studies investigating causality and evaluation of the association between insomnia and BMI.