Changes in insulin sensitivity, secretion and glucose effectiveness during menstrual cycle

Several clinical conditions suggest an effect of sex steroids on glucose homeostasis in women. Studies examining this phenomenon have yielded controversial results.

To investigate the effect of the menstrual cycle on insulin sensitivity, glucose effectiveness and acute insulin response to glucose using the tolbutamide-modified intravenous glucose tolerance test (IVGTT) during the follicular (day 8 +/- 1) and luteal (day 23 +/- 1) phases of the menstrual cycle, the authors recruited 12 healthy regularly menstruating women. All had fasting glucose concentration of < 100 mg/dl [corrected] (89.7 +/- 6.2) with no family history of diabetes mellitus; their body mass indices were < 25 kg/m2 (22.41 +/- 1.44 kg/m2).

The mean insulin sensitivity (Si) values decreased during the cycle. Insulin sensitivity (Si x 10(-4)/min.mU/ml) was higher in the follicular phase (5.03 +/- 0.72) and decreased in the luteal phase (2.22 +/- 0.45) (p < 0.001). Glucose effectiveness (Sg min-1) did not change as a function of the phase of the menstrual cycle. Sg estimates were 0.0229 +/- 0.00323 in the follicular phase, and 0.0225 +/- 0.00319 (p = NS) in the luteal phase, respectively. Acute insulin response (AIRg mU/ml) was 276.4 +/- 27.8 in the follicular phase. An adaptive increase (304.4 +/- 51.1) in response to the insulin resistance during the luteal phase was observed, but this increase was not statistically significant (p = NS).

Knowledge of the variations in insulin sensitivity that occur during the normal menstrual cycle provides a basis of comparison for studies of other clinical conditions. Also, this phenomenon should be considered if the determination of insulin resistance is the purpose of certain epidemiological studies.