Environmental and behavioral determinants of fasting plasma glucose in women. A matched co-twin analysis.

Comparing results of an unmatched analysis in a sample of unrelated persons created by randomly selecting one twin from each pair with results of a matched monozygotic co-twin analysis provides a means of distinguishing environmental influences from genetic influences on a dependent variable of interest. Determinants of the fasting plasma glucose level were investigated in a large sample of adult female nondiabetic twins from the Kaiser Permanente Twin Registry. In the subsample of unrelated persons, fasting plasma glucose was significantly and positively associated with age, body mass index, uric acid level, and alcohol intake and was significantly inversely related to leisure time physical activity. When monozygotic twins were treated as matched pairs, only the effects of body mass index and alcohol consumption remained significant, whereas the association with leisure time physical activity was greatly reduced and no longer statistically significant. These results suggest that behavioral and therefore alterable aspects of obesity and alcohol consumption influence the fasting plasma glucose level; alcohol consumption may be a risk factor for non-insulin-dependent diabetes mellitus; and common underlying genetic factor(s) may be responsible for the negative association between physical activity and fasting plasma glucose.