Similar seasonality of birth in type 1 and type 2 diabetes patients: A sign for common etiology?

Birth seasonality in juvenile-onset type 1 diabetes (T1D) has been repeatedly described. Seasonality of birth for adult-onset type 2 diabetes (T2D), however, has never been reported. To study whether abnormal seasonality of birth exists for T2D, we compared the month-of-birth pattern in T2D patients to those in Ukraine general population. A total of 60,589 cases, restricted to persons born before 1960 and diagnosed with T2D after age 40, were identified from three Ukraine regional diabetes registers (Chernyhiv, Kherson, and Rivne). Reference populations was based on Ukraine census 2001 depersonalised data (n = 1,573,040). Seasonal patterns were estimated using logistic regression with second order harmonic terms. Combining cohorts from all regions studied revealed a significant seasonal pattern of T2D incidence rates (p < 0.001). Surprisingly, this pattern with peak in 7 May and trough in 22 December was quite similar to that previously obtained by us for T1D (peak in 29 April and trough in 29 December) [1]. Current classifications distinguish between autoimmune-related T1D and insulin resistance-related T2D. However, convergence of their phenotypes over recent years, relationship of weight gain to the risk of T1D and finding of autoantibodies in patients with T2D (reviewed in [2]), provide evidence for overlap in etiology between T1D and T2D. A recent NOD mouse study provides genetic evidence for this overlap [3]. The accelerator hypothesis [2] argues that T1D and T2D, rather than being different, are merely poles of a single pathological spectrum. Our finding that T1D and T2D share similar seasonality of birth has implications for hypotheses, such as accelerator hypothesis, that propose common etiology for both diseases. Early-life seasonal influences (nutrition, infections, insolation etc.) are likely among etiological factors. Season-ofbirth risk factor may improve risk stratification for diabetes development.