Association between BMI trajectories and metabolic syndrome in postmenopausal women: a cross-sectional study from NHANES 1999-2018.

BACKGROUND: Obesity is an established risk factor for metabolic syndrome (MetS), with both conditions being particularly prevalent among postmenopausal women. However, research examining the relationship between body mass index (BMI) changes across the lifespan and MetS in this specific population remains limited. This study aims to explore the association between BMI trajectories and MetS risk in postmenopausal women. METHODS: This cross-sectional study included postmenopausal women aged ≥ 60 years from the National Health and Nutrition Examination Survey 1999-2018. MetS was defined by 2009 Joint Interim Statement criteria. BMI trajectories over time were identified using latent class growth mixture modeling. Multivariable logistic regression analyses were performed to evaluate the association between distinct BMI trajectories and MetS risk. Subgroup analyses based on reproductive characteristics were conducted to investigate potential effect modification in the relationship between BMI trajectories and MetS risk. RESULTS: Among 4061 eligible participants, the overall prevalence of MetS was 71.57% (n = 3070). Three distinct BMI trajectories were identified: stable trajectory (n = 3047, 76.34%), increasing trajectory (n = 540, 12.30%), and increasing-decreasing trajectory (n = 474, 11.36%). Compared with the stable trajectory group, participants in the increasing trajectory group had a higher risk of MetS (OR = 5.09, 95% CI: 3.19-8.13), while those in the increasing-decreasing trajectory group had the highest risk of MetS (OR = 5.89, 95% CI: 3.73-9.31). Subgroup analyses revealed significant effect modification of the association between BMI trajectories and MetS risk by early menopause (P = 0.059), early age at first live birth (P < 0.05), and high parity (P < 0.05). CONCLUSIONS: The increasing and increasing-decreasing BMI trajectory groups are associated with a higher risk of MetS in postmenopausal women. This association is significantly modified by reproductive characteristics. Maintaining a long-term stable BMI may benefit metabolic health.