Seasonal variation of birth month and breastfeeding in children with diabetes mellitus

OBJECTIVE: As breastfeeding is suggested to protect against diabetes mellitus we decided to investigate whether the seasonal variation of month of birth of diabetic children, with more diabetes in children born in summer, can be explained to some extent by a seasonal variation of exclusive breastfeeding. PATIENTS: A population-based group of 297 children who had been diagnosed with diabetes mellitus before the age of 15 years was compared with 792 matched healthy subjects. RESULTS: There was no difference in duration of breast-feeding between children who later got diabetes and the controls. Children (both diabetics and controls) born during the summer were exclusively breastfed for a mean period of 2.2 months. Corresponding figures for children born during winter were 2.8 months (p<0.04), spring 2.5 months (n.s.) and autumn 2.7 months (p<0.05). Seasonality was most pronounced in children who developed diabetes between the ages of 10 and 15 years. CONCLUSION: These results indicate that children born during the summer, who have increased risk of developing diabetes mellitus, have also been exclusively breastfed for a shorter time.