Natural environmental factors at birth on risk for rheumatoid arthritis: the impact of season, temperature, latitude, and sunlight exposure.

Abstract

Background: Environmental factors contribute to approximately 41% of the risk of rheumatoid arthritis (RA). Previous studies have focused on anthropogenic environmental factors, while much less attention has been given to natural environmental factors. Our study explored the potential influence of natural environmental factors at birth on the risk of RA.

Methods: This large retrospective study utilized data from the China Kadoorie Biobank. A restricted cubic spline (RCS) model was employed to explore nonlinear relationships between natural environmental factors and the risk of RA. Additionally, a multivariable Cox regression model, adjusted for confounding factors, was used to examine correlations between season of birth, geographic, climate, and the risk of RA.

Results: A total of 512,715 participants were included in this study, of which 2889 (0.56%) were diagnosed with RA. The RCS analysis revealed that the monthly average temperature at birth (p < 0.001), the latitude (p = 0.027) of the birthplace, and the sunshine rate (p < 0.001) exhibited a nonlinear relationship with the risk of RA. Multivariable Cox regression analysis revealed that participants born in Spring and Summer (HR 1.13, 95% CI 1.05-1.23) had an increased risk of RA compared to those born in Autumn and Winter. Additionally, participants born at latitudes ≤ 24°N (HR 1.49, 95% CI 1.32-1.68), with sunshine rate ≤ 28% (HR 2.00, 95% CI 1.75-2.29) or ≥ 60% (HR 1.22, 95% CI 1.08-1.38) had an increased risk of RA. Being born in regions with a monthly average temperature ≥ 27 °C (HR 0.82, 95% CI 0.72-0.95) was associated with a decreased risk of RA.

Conclusion: Being born in Spring and Summer, as well as early-life exposure to low-latitude regions and extreme sunlight environments increases the risk of RA. Our study revealed significant associations between the risk of RA and natural environmental factors at birth, emphasizing the impact of the early-life environment on the onset of RA.