Associations between female reproductive factors and osteoarthritis in women ≥ 50 years old: An NHANES 1999-2018 analysis of more than 10,000 women.

Osteoarthritis (OA) is the most common form of arthritis, and as the population ages, the incidence and prevalence of OA are projected to rise, particularly affecting women. This study investigates the association between female reproductive factors (age at menarche, menopause, gravidity, parity, and reproductive lifespan) and OA in women ≥ 50 years old using data from the United States National Health and Nutrition Examination Survey (NHANES). NHANES data from 1999 to 2018 of women ≥ 50 years old with complete arthritis questionnaires and other data of interest were reviewed. Reproductive factors were analyzed as continuous and ordinal variables. Covariates included age, race/ethnicity, body mass index (BMI), poverty income ratio, smoking status, and comorbidities such as hypertension, cardiovascular disease, and diabetes. A total of 10,133 women were included in the analysis. A later age at menarche was associated with a lower likelihood of OA (adjusted odds ratio [aOR] = 0.91, 95% confidence interval [CI]: 0.87-0.95, p < 0.001), and higher parity was associated with a lower likelihood of OA (aOR = 0.94, 95% CI: 0.91-0.97, p < 0.001). Stratified analysis showed that these associations were evident in specific subgroups, including women aged 60-69 years and those with obesity, but were not observed in other groups. Later age at menarche and higher parity are associated with a lower likelihood of OA in women. The cross-sectional nature of the study limits causal inferences; thus, further research is needed to explore potential causality.