The relationship between multiple sex partners and anxiety, depression, and substance dependence disorders: a cohort study.

Changes in sexual behavior have resulted in longer periods of multiple serial or concurrent relationships. This study investigated the effects of multiple heterosexual partners on mental health, specifically, whether higher numbers of partners were linked to later anxiety, depression, and substance dependency. Data from the Dunedin Multidisciplinary Health and Development Study, a prospective, longitudinal study of a birth cohort born in 1972-1973 in Dunedin, New Zealand were used. The relationship between numbers of sex partners over three age periods (18-20, 21-25, and 26-32 years) and diagnoses of anxiety, depression, and substance dependence disorder at 21, 26, and 32 years were examined, using logistic regression. Interaction by gender was examined. Adjustment was made for prior mental health status. There was no significant association between number of sex partners and later anxiety and depression. Increasing numbers of sex partners were associated with increasing risk of substance dependence disorder at all three ages. The association was stronger for women and remained after adjusting for prior disorder. For women reporting 2.5 or more partners per year, compared to 0-1 partners, the adjusted odd ratios (and 95 % CIs) were 9.6 (4.4-20.9), 7.3 (2.5-21.3), and 17.5 (3.5-88.1) at 21, 26, and 32 years, respectively. Analyses using new cases of these disorders showed similar patterns. This study established a strong association between number of sex partners and later substance disorder, especially for women, which persisted beyond prior substance use and mental health problems more generally. The reasons for this association deserve investigation.