Blue eyes as a risk factor for type 1 diabetes

Background: A high frequency of blue eyes and fair skin are reported in northern European Caucasians with type 1 diabetes (T1D). Also there is an inverse relationship between latitude and T1D incidence. We determined whether iris colour and skin pigmentation are risk factors in a Caucasian population living in two Mediterranean regions located at the same latitude with higher ultraviolet B irradiance, but with different T1D incidence.

Methods: We studied iris colour in 281 consecutive subjects with T1D and 298 controls. Skin type was evaluated by melanin quantification.

Results: In Lazio, blue eyes and fair skin type are significantly more common in T1D subjects than in controls (21 versus 9%, p = 0.002; 50 versus 35%, p < 0.001, respectively). In Sardinia, the frequency of blue eyes in T1D subjects is twice that in controls (5.8 versus 2.6% and significantly higher when compared to the expected calculated frequency in the entire population). By logistic regression analysis, only blue eyes are independent and significant predictors of T1D [odds ratio for blue eyes = 2.2; 95% confidence interval (1.1-4.4), p = 0.019].

Conclusions: As previously shown in a Caucasian population from northern Europe, blue eyes and a trend for fair skin increase the risk for T1D also in a Caucasian population born and residing in a Mediterranean region (Continental Italy). This finding may be relevant for explaining different T1D incidence as prevalence of blue eyes differ substantially between northern and southern European Caucasians.