Diabetes, Vol 36, Issue 3 265-268, Copyright © 1987 by American Diabetes Association
Seasonality in glycosylated hemoglobin in normal subjects. Does seasonal incidence in insulin-dependent diabetes suggest specific etiology?
MJ MacDonald, L Liston and I Carlson
Seasonality in the diagnosis of insulin-dependent diabetes mellitus (IDDM),
i.e., increased incidence in winter, was the impetus for this study of
seasonality in glycosylated hemoglobin levels in nondiabetics. Glycosylated
hemoglobin levels of 35 nondiabetic children and adults were highest at the
ends of autumn and winter and lowest at the ends of spring and summer (P
less than 10(-4)). This result is consistent with reports of seasonal
variation in blood glucose, with the highest levels occurring in winter, as
well as reports that suggest an internal milieu of increased counterinsulin
action in winter due to seasonality in counterinsulin hormones, dietary
factors, body weight, amount of exercise, growth rates in children, and
ambient temperature. IDDM is caused by the gradual destruction of the
pancreatic insulin-producing cells via lymphocytic infiltration--a process
that may occur over years. We conclude that a decreased carbohydrate
tolerance associated with winter can explain the seasonal variation in the
incidence of IDDM and that this seasonality is caused by the precipitation
of overt carbohydrate intolerance in individuals with already seriously
compromised insulin secretory capacity. This implies that seasonality is
not very formative about the cause of the destruction of pancreatic
insulin-producing cells.