What Happens after Sex

What Happens after Sex

The time partners spend together after sex is markedly important for bonding as a couple. According to Daniel Kruger, research assistant professor at U-M SPH, understanding new ways to encourage relationship commitment and stability has implications for promoting sexual and emotional health—and for preventing the spread of sexually transmitted infections (STIs). Two recent studies by Kruger and his colleague Susan Hughes of Albright College suggest that couples should use the so-called "post-coital time interval" (PCTI) to strengthen their attachment to one another. "Our research shows that expressions of love and commitment are especially important in this time span, because people are experiencing a cascade of emotions and hormonal activity," says Kruger.

The first of the studies by Kruger and Hughes examines how gender differences affect people's PCTI experiences. The second study demonstrates that individuals with partners who tend to fall asleep first after sex have a greater desire for partner expressions of emotional bonding, physical affection, and communication, which can in turn affect relationship commitment.

The significance of the post-coital time interval may be most relevant when there is ambiguity as to whether the relationship is long-term and exclusive. In particular, says Kruger, "couples who want to establish a long-term relationship should use the PCTI as an opportunity for bonding."

It's an important public health issue, Kruger adds. If people switch partners less frequently, it can reduce their risk of STI transmission. He explains, "People these days have a casual relationship with sex—despite the fact that one act of sex could change your life."
—Danielle Taubman, MPH '13

Personality and Heart Disease

Studies show that personality measures—including traits such as patience and aggression—can predict both heart disease risk and a person's overall prospects for healthy aging. And that's got biostatistician Goncalo Abecasis wondering whether he and his research team can find specific genes capable of predicting personality or changing heart disease risk factors. "The idea would be that once you've found a specific gene, you could try to design a drug that either copies or blocks its effect, depending on the outcome you're after," says Abecasis, the Felix E. Moore Collegiate Professor of Biostatistics.

But it's much more difficult to identify genes associated with personality than it is to find genes linked to more physical measures like cholesterol and blood pressure levels—which Abecasis has had considerable success doing. That's because when it comes to personality, he says, more genes are likely to be involved, and so the impact of any one specific gene will be smaller. In an effort to disentangle the mystery, he and his team have devised new and better ways to sequence the human genome and are using that methodology to parse the genomes of 1,000 individuals. They hope to learn more about human personality and how such information can be used to reduce the risk of heart disease. The cohort is a subset of a larger genetic study focused on aging.

"It's very clear that genes and genetic variants contribute to personality," Abecasis says. "But it seems like most of them only make very small contributions, so it's hard to pinpoint something and say, ‘Aha! This variant makes you more agreeable or more neurotic, and therefore at a lower or higher risk for heart disease.'"

One finding to have emerged from their work is that genetic factors that change good cholesterol (HDL) have no impact on the risk of heart disease. "So HDL is probably not directly linked to heart disease," Abecasis says. The findings shed light on why drugs that have been developed to alter HDL have not worked especially well.