No seasonal variation of insulin sensitivity and glucose effectiveness in men

Insulin resistance is of pathogenetic importance for the development of non -insulin-dependent diabetes mellitus (NIDDM). However, not much is known ab out the variation in insulin sensitivity in the individual over longer peri ods. Consequently, we measured insulin sensitivity (Si) and glucose effecti veness (Sg) in healthy young men (N = 10) 5 times over a period of 15 month s using a frequently sampled intravenous glucose tolerance test (FSIVGTT) w ith minimal-model analysis (study of seasonality). The maximal aerobic capa city ((V) over dot O(2)max), fat-free mass, body mass index (BMI), and 24-h our ambulatory blood pressure (BP) were also assessed. Furthermore, we perf ormed a study designed to evaluate the day-to-day variation in Si and Sg (s tudy of day-to-day variation). Here, we studied Si and Sg in healthy young men (n = 8) within 2 weeks. In the study of seasonality, the coefficient of variation (CV) for Si was 24.0%, whereas the CV for Sg was 26.0%. Anticipa ting a seasonal variation in Si following a sine curve with a cycle length of 1 year and an unknown phase and amplitude, we tested this hypothesis wit h a multiple linear regression model that allows for different levels of Si between individuals, and failed to detect any impact due to this. Si (mean +/- SD, 1.17 +/- 0.28 x 10(-4).min(-1).pmol/L-1, P = .38), Sg (0.023 +/- 0 .006 min(-1) P = .71), fasting insulin (21.2 +/- 7.3 pmol/L, P = .98), (V) over dot O(2)max (3.8 +/- 0.6 L/min, P = .13), and fat-free mass (64.9 +/- 2.5 kg, P = .92) were constant over time. In the study of day-to-day variat ion, we found a CV for Si of 17.3% and a CV for Sg of 23.3%. In conclusion, we found that the variations in Si and Sg were slightly higher than those found in studies performed to establish the day-to-day variation. However, no significant seasonal variation in Si and Sg was evident in this group of healthy young lean caucasian men. Consequently, indices of Si and Sg obtai ned at different times of the year appear comparable. Copyright (C) 2000 by W.B. Saunders Company.