"Sex makes you feel good, not just because it releases more hormones or endorphins but also because you will feel more affection with your partner," said clinical psychologist Anik Debrot of the University of Lausanne in Switzerland, lead author of one of the studies. "It doesn't matter if you're a man or a woman, affection is a very important reason that sex feels good to you."
"It's well known that sex often produces a short-term afterglow," said CNN contributor Ian Kerner
, a psychotherapist who specializes in sex and couples therapy. "This study demonstrates that sense of well-being and connection extends beyond the bedroom."
In the first two studies, Debrot and her colleagues polled American men and women in romantic relationships -- both heterosexual and homosexual -- that ranged from four months to 30 years long. They were asked not only about their sexual frequency and level of positive emotion but about how often they touched or showed other signs of affection.
"Lots of studies have shown people who have more sex have better health and well-being but little to explain why," Debrot said. "It could be, for example, that people with a higher sense of well-being or better health have more sex. In our studies, we wanted to see how much affectionate touch played a role."
The results mirrored previous science, but with a twist. Not only were people who had frequent sex more satisfied with life, displays of affection played an important role in explaining that association, even in men.
"This was surprising," Debrot said, "since research has found gender differences in how men and women approach sexuality, and we always think of women as the ones who associate sex with affection."
The next two studies looked at how sexual activity and affection during the ups and downs of daily life affected the emotional well-being of each romantic partner over extended periods of time. The researchers did this by training each couple in the use of handheld devices to record their sexual and erotic activity, emotional well-being, and verbal and non-verbal expressions of affection four times each day.
"We defined affection as interactions the person perceived as showing care and fondness toward another person," Debrot explained. "Loving and tender moments, such as thoughtful signs, touches or actions by one partner to the other."
More sex equals more affection
The results showed that having sex predicted more affection in the moments after sexual intimacy but also hours later, even in couples with children or those married long past the "honeymoon period." Moreover, for couples who felt more positive emotions after sex, the effects were still evident six months later.
"The more overall sex they had, the more affection; the less sex they had, the less positive affection," Debrot said, adding that it didn't have to be intercourse. "Moments that were experienced as erotic or sexually arousing were just as predictive of positive emotions."
This study was interesting and unique, says Kerner, because it used electronic questionnaires to capture a level of real-time measurements of how sex and affection are intertwined.
"It showed that sex has a kind of 'half-life' of relational positivity and needs to be maintained and replenished," Kerner said, adding that he often sees this in the couples he counsels.
"Many therapists like to say that sex is only 20% of a relationship, but in my experience, when couples are not having sex, it can feel like 100% of a relationship.
"There is often a breakdown of communication, with partners often lashing out or, conversely, self-silencing," Kerner said. "In addition, it's not uncommon for non-sexual physical intimacy and affection to also fall by the wayside."
But when couples keep the sexual dimension of their relationship alive and intact, Kerner says, "it leads to an overall warming up of the relationship, which includes more touch and non-sexual affection as well as higher level of regard towards their partner."
Evolutionarily, these results make sense, says Debrot: Since close bonds are essential for survival, sex can help keep the couple together to take care of children.
"The sharing, emotional aspects of sex are critical to our well-being," she added. "People who are motivated to please their partner, and motivated to make their partner happy, they are more satisfied and have a more satisfied partner, both sexually and in the relationship."
People who share positive and exciting activities in their daily lives increase the possibility of having sex, she adds, stressing that couples should make sure they schedule time to build their relationship.
"Having sex takes time, and building a strong relationship takes time," Debrot said. "Couples should preserve some quality time for this to happen."