Frontiers in endocrinology
Calendar month seasonality of HbA1c and its phase relationship with climatological temperature in 633,838 clinical measurements
By Li K and Xia F.
Abstract
Objective
HbA1c reflects glucose exposure over the preceding 8-12 weeks. We characterised the lagged seasonal association between monthly climatological temperature normals and HbA1c in a 12-year hospital cohort and examined whether a similar pattern was present in patient-level records. Research design and methods: We analysed 633,838 HbA1c measurements (387,678 patients; 633,737 with complete covariates) from a Chinese tertiary hospital (2014-2025). Cross-correlation was assessed for lags of 0-6 months using monthly HbA1c means and fixed monthly climatological temperature normals. Patient-level distributed-lag regression with cluster-robust standard errors and generalised estimating equations was used as a complementary analysis.
Results
HbA1c was inversely correlated with the climatological temperature series most strongly at a 2-month lag (r = -0.297, P < 0.001) rather than concurrently (r = -0.127, P = 0.14). Pooled by calendar month, the lag-2 seasonal association was strong (r = -0.977, R² = 0.955), with a seasonal HbA1c amplitude of 0.235% (2.6 mmol/mol; peak March, trough September), strongest under age 60 and attenuated during COVID-19. Patient-level regression showed a similar lag pattern, with the largest coefficient at lag 2 (β = -0.0088% per °C; 95% CI -0.0093 to -0.0082; P < 0.001), and the individual-level partial R² was 0.15%.