The more sex partners young adults have the more likely they are to go on to develop alcohol or cannabis dependence disorders in young adulthood, according to new University of Otago research.
The findings, which emerge from the long-running Dunedin Multidisciplinary Health & Development Study, show young people are at greater odds of developing these substance disorders with increasing numbers of sexual partners. The odds were much greater for young women. The research is believed to be the first anywhere to examine the effect of multiple sex partners on aspects of mental health in young adulthood in a general population sample.
Using data from the world-renowned study, which has closely tracked the health and behaviour of more than 1000 people since their birth in Dunedin in 1972-73, the researchers examined how many sex partners the study members reported during three age periods (18-20, 21-25 & 26-31 years). They then looked at data on their mental health immediately after each period (at ages 21, 26, and 32), including anxiety, depression and substance dependence.
Substance dependence disorder involves not only significant use of the substance but also impairment in social, occupational or recreational activities.
The research is newly published online in the US journal Archives of Sexual Behavior.
Study lead author Dr Sandhya Ramrakha says the strong link between multiple sex partners and later substance disorders remained even after the researchers took into account any prior mental disorder, including alcohol and cannabis disorders.
"This ruled out the possibility that the men and women already had substance problems and that this had led to them having more sexual partners," Dr Ramrakha says.
The researchers found that women who had 2.5 or more partners per year (compared to none or one partner) greatly increased their odds of having a substance dependence disorder in each age period. The odds increased between seven and 17 fold.
"This is a striking increase in the risk of substance disorder. Furthermore, when we used a model to compare men and women who had more than 10-20 sex partners in the same periods, we found that these women were much more likely to have a substance disorder than the men," she says.
The researchers suggest several possible explanations for the intertwining of these behaviours. Among these is that multiple partners and alcohol/cannabis use are part of a cluster of risk-taking behaviours that happen in adolescence and young adulthood. Or it may be due to the disinhibitory effects of alcohol and cannabis providing opportunities for sexual behaviour.
Context may be another explanation, that is, pubs and bars are also places where one can easily meet partners.
"The role of the alcohol industry in encouraging the view that alcohol is entertainment, targeting young women in particular, is disturbing. Young women are also encouraged to 'keep up' with young men in relation to their drinking.
"Another important possibility is that there is something about having multiple partners itself that puts people, especially women, at risk of substance disorders. For instance, it may be the impersonal nature of short-term relationships, or the effect of multiple failed relationships.
"Women with only one sex partner in each period seem to be protected from substance dependence."
Dr Ramrakha says that more research is needed to determine what is behind the link so that solutions can be found.
Explore further: Heavy drinking, conduct disorder linked to high-risk sexual behavior
Research fact sheet (PDF).