Wednesday, August 13, 2008

Contraceptive pill influences partner choice

The contraceptive pill may disrupt women's natural ability to choose a partner genetically dissimilar to themselves, research at the University of Liverpool has found.

Disturbing a woman's instinctive attraction to genetically different men could result in difficulties when trying to conceive, an increased risk of miscarriage and long intervals between pregnancies. Passing on a lack of diverse genes to a child could also weaken their immune system.

Humans choose partners through their body odour and tend to be attracted to those with a dissimilar genetic make-up to themselves, maintaining genetic diversity. Genes in the Major Histocompatibility Complex (MHC), which helps build the proteins involved in the body's immune response, also play a prominent role in odour through interaction with skin bacteria. In this way these genes also help determine which individuals find us attractive.

The research team analysed how the contraceptive pill affects odour preferences. One hundred women were asked to indicate their preferences on six male body odour samples, drawn from 97 volunteer samples, before and after initiating contraceptive pill use.

Craig Roberts, a Lecturer in Evolutionary Psychology who carried out the work in collaboration with the University of Newcastle, said: "The results showed that the preferences of women who began using the contraceptive pill shifted towards men with genetically similar odours.

"Not only could MHC-similarity in couples lead to fertility problems but it could ultimately lead to the breakdown of relationships when women stop using the contraceptive pill, as odour perception plays a significant role in maintaining attraction to partners."

Causes for sexual dysfunction change as people age

Earlier experiences with multiple partners and STDs take their toll

Sexual dysfunction is not an inevitable part of aging, but it is strongly related a number of factors, such as mental and physical health, demographics and lifetime experiences, many of which are interrelated, according to a new study by researchers at the University of Chicago.

The study, funded by the National Institutes of Health, found that a history of sexually transmitted disease also has an impact on sexual health later in life. People who had an STD are also more likely to have had sexual experiences over their lifetimes that included more risks and multiple sex partners.

"Having had an STD roughly quadruples a woman's odds of reporting sexual pain and triples her lubrication problems," said Edward Laumann, the George Herbert Mead Distinguished Service Professor of Sociology at the University, and lead author of the paper, "Sexual Dysfunction Among Older Adults: Prevalence and Risk Factors from a Nationally Representative U.S. Probability Sample of Men and Women 57 to 85 Years of Age," published in the current issue of the Journal of Sexual Medicine.

Men are more than five times as likely to report sex as non-pleasurable if they have previously had an STD.

Laumann was joined in writing the paper by University researcher Aniruddha Das, and Linda Waite, the Lucy Flower Professor in Sociology at the University.

The study showed that women may be more likely than men to experience sexual dysfunction because of health issues. The most common problem for men is erectile dysfunction, a problem that increases with age.

"The results point to a need for physicians who are treating older adults experiencing sexual problems to take into account their physical health and also consider their mental health and their satisfaction with their intimate relationship in making any assessment," Laumann said.

The study is based on interviews with a national sample of 1,550 women and 1,455 men, ages 57 to 85, who were part of the 2005-2006 National Social Life, Health and Aging Project, a nationally representative survey of community-dwelling older U.S. adults. The survey collected data on social life, sexuality, health, and a broad range of biological measures.

The study is a companion to a 1999 study Laumann led that looked at sexual dysfunction among men and women, ages 18 to 59. That study found that physical health was a bigger predictor of sexual problems for men than it was for women. For that younger age group, having an STD did not increase the odds of experiencing sexual dysfunction.

The new study found that among older women, a common factor correlated with sexual dysfunction was urinary tract syndrome, which was associated with decreased interest in sex, as were mental health issues such as anxiety.

Among men, mental health issues and relationship problems contributed to a lack of interest in sex and the inability to achieve orgasm, while being treated for urinary tract syndrome was associated with trouble maintaining and achieving an erection.

Daily alcohol consumption seems to improve a woman's sexual health, increasing her interest and pleasure in sex. Among men, there was no reported impact of alcohol consumption.

Demographic characteristics and cultural factors also are related to sexual performance, the study found. Hispanic women were twice as likely to report pain during intercourse. Among men, blacks were twice as likely to report a lack of interest in sex and more likely to report climaxing too early.