Similarity in saliva cortisol measures in monozygotic twins and the influence of past major depression

Background: Some studies suggest that cortisol may be under genetic control. The aims of our study were to investigate the familial resemblance in morning and evening cortisol secretion as assessed by saliva cortisol and to assess the influence of history of major depression. Methods: Women for this investigation were selected from an ongoing study in female–female twin pairs ascertained from the Virginia Twin Registry. Telephone screening assured that current inclusion/exclusion criteria were met. Subjects were asked to collect samples within 45 min after awakening, and evening samples immediately before bedtime for 14 days. Results: There was a high degree of correlation across weeks in both the and cortisol values, indicating significant stability across individuals. There was significant correlation between and cortisol in monozygotic twins. In twins with a history of major depression (n = 30), compared with the twins without past major depression (n = 28), there was a trend towards higher cortisol (p = .056). Conclusions: These results suggest that around 40–45% of the total variance in salivary cortisol is shared by monozygotic twins. Although the increase in baseline cortisol in twins with a history of major depression is only significant at the trend level, the effect size is comparable to an “in episode” depressed population