t.germeau / Flickr (CC BY 2.0) An impressive amount of research has linked frequency of sex with greater happiness. One study even put a monetary estimate on it. They said that the happiness spurt from having sex once a week compared with monthly is similar to the boost you’d get from earning an extra $50,000 a year (though for anything more frequent than weekly sex, the benefits seemed to tail off).

Asking if and why more sex makes us happier may sound like asking the blindingly obvious, but of course a lot of pleasurable activities don’t have long-term emotional benefits; it’s also tricky to rule out the simple alternative possibility that we’re more likely to have sex if we’re happy.

In a series of studies in Personality and Social Psychology Bulletin, psychologists in Switzerland and Canada have looked beyond the immediate bliss that sex can bring, and they say that the main reason that more sex seems to contribute to greater long-term happiness is because of all the cuddling (and other expressions of affection) that’s involved, both at the time, and for hours afterwards.

In Talking It Over, Julian Barnes writes that “Love is just a system for getting someone to call you darling after sex”; this new research suggests that sex is a system for getting someone you love to call you darling, and to give you a big cuddle.

Anik Debrot at the University of Fribourg and her colleagues conducted two surveys, the first involving 335 participants, recruited on Amazon’s Mechanical Turk site, who were in a romantic relationship, and the second involving both partners in 74 couples recruited in the San Francisco Bay Area in California. The vast majority of participants were heterosexual. They answered questions about how often they had sex, about how much affectionate touch went on in their relationship (e.g. cuddling, hugging, kissing and caressing) and rated their life satisfaction or how much they typically experienced positive emotions like joy and contentment.

Having more sex was correlated with greater life satisfaction and experiencing more positive emotions, consistent with past research. But when the researchers factored amount of affection into the equation, the sex–happiness link all but disappeared (with one exception – to the researchers’ surprise they found this wasn’t true for women in the second survey). The overall implication of the surveys was that more sex leads to more happiness because it promotes affection.

The researchers also conducted two “experience-sampling” studies. The first involved 106 couples, most of them married, with children. Each participant kept a diary for ten days, noting their sexual activity, including any erotic moments; their affectionate experiences, including “moments of love and security” and “affectionate or thoughtful signs from my partner”; and their emotions. They kept these records in the morning before work; after work; during the 45 minutes after reunion with their partner; and during the last hour before bed.

Similar to the earlier surveys, this showed that sex in the preceding 24 hours was associated with feeling more positive emotions in the morning, but that this correlation was greatly reduced once affection in the preceding 24 hours was taken into account. In other words, sex seemed to lead to positive emotions because sex tended to go hand with love and cuddles. Indeed, sex without affection was extremely rare (this only happened on 4.2 per cent of occasions according to the diaries).

The researchers also caught up with these couples six months later. More sex during the diary part of the study foretold greater relationship satisfaction all these months later, but only when that earlier sex had been associated with the experience of positive emotions.

A methodological challenge for this topic is that it’s not easy to conduct a controlled experiment in which you instruct participants how much sex or cuddling to get involved in and then look at the effects on their well-being (even if you tried such a study, it wouldn’t exactly be comparable to real-life). To try to get round this, the researchers looked to see whether sex at one time point was associated with more affection later on, which would help support their ideas about how sex promotes affection.

To this end, the final study involved 58 heterosexual couples keeping notes on their sexual activity and affection (defined here as “moments of love and affection”) via a smartphone several times a day for two weeks: at waking, at midday, at 6pm and before going to bed. This showed that when participants reported having sex at one time point, they were more likely to report experiencing affection not just at that time, but also at the next data entry hours later. This still doesn’t prove sex causes affection and that affection causes the happiness that’s previously been linked with sex, but it’s consistent with that interpretation of things.

Debrot and her team said their studies represented a rare attempt to bridge the typically separate fields of sex research and relationship research. “When engaging in sex, people not only seek an intimate connection, but indeed experience more affection, both when having sex and in the next several hours,” they said. “Hence sex seems not only beneficial because of its physiological or hedonic effects, but because it promotes a stronger and more positive connection with the partner.”

They added that their findings could help some couples – for example, at times when sex isn’t possible for whatever reason, the results suggest that making the effort to be affectionate could be beneficial for wellbeing and the relationship. Conversely, the researchers said, “sexual activity might compensate for the diminished well-being in partners having difficulties adequately exchanging affection.”