Seasonality in Glycosylated Hemoglobin in Normal Subjects: Does Seasonal Incidence in Insulin-Dependent Diabetes Suggest Specific Etiology?

Abstract

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.

Clinical pattern of childhood Type 1 (insulin-dependent) diabetes mellitus in the Sudan

“…A higher number of patients were diagnosed during the cooler months of the year compared to the warmer ones. This finding is consistent with global reports from both Northern and Southern hemispheres [18][19][20][21] and has been cited as evidence of a possible role for environmental factors in the aetiology of Type i diabetes [22].…”

Exposure to low outdoor temperature in the midtrimester is associated with low birth weight

“…Seasonal changes in hormonal systems, such as thyroid axis and glucose control, have previously been shown 19–21 . Glycosylated haemoglobin has been shown to be approximately 0.4% lower in the summer than in the winter, indicating that there is a relative worsening of insulin sensitivity in the winter 22 . To corroborate this, Behall et al .…”

Metabolic adaptation of mice in a cool environment

“…In hibernators, body fat levels show predictable increases and decreases with seasonal changes in response to sensing of environmental factors or by responding to the timing of an endogenous clock [1,13]. Although humans do not hibernate and thus have less need to store energy, several reports have shown seasonal variation in metabolic diseases including insulin-dependent diabetes mellitus, which peaks during winter months [10,15], in blood glucose concentration and insulin sensitivity in healthy people [2,11] and in blood glucose concentration in patients with type 2 diabetes [9]. In addition, some cases of type 2 diabetes and cardiovascular disease have been reported to be caused by biological interactions related to seasonal changes [17].…”