If you think getting lots of sex is one key to happiness, think again, researchers say; while people with healthy sex lives are generally happy, it's not necessarily linked to the amount of sex they're having.
To investigate whether there is a causal relationship between sexual frequency and happiness, researchers at Carnegie Mellon University gathered 128 couples into two groups, one of which was instructed to have more sex - double their normal weekly intercourse frequency - than the other group.
The researchers used online questionnaires to track all the couples' happiness over the 3 months of the study.
At the end of the study period those couples having sex more frequently than was normal for them actually experienced a slight decrease in their happiness, the researchers reported in the Journal of Economic Behavior & Organization.
The researchers were quick to acknowledge that having more frequent sex didn't decrease the desire for sex or the enjoyment of it; instead, they suggested, the reported slight decrease in happiness was likely down to the fact of being asked to increase the frequency rather than being able to exercise their normal choices of initiating sex on their own.
"Perhaps couples changed the story they told themselves about why they were having sex, from an activity voluntarily engaged in to one that was part of a research study," says lead study investigator George Lowenstein.
"If we ran the study again, and could afford to do it, we would try to encourage subjects into initiating more sex in ways that put them in a sexy frame of mind, perhaps with baby-sitting, hotel rooms or Egyptian sheets, rather than directing them to do so," he says.
Despite the findings of the admittedly small and limited study, Lowenstein says he believes many couples tend to have sex too seldom, and that increasing the frequency of intercourse - in the right way - can increase happiness in a relationship.
Study co-author Tamar Krishnamurti says the findings could help couples increase their happiness by improving their sex lives, and not necessarily in terms of how often they engage in the act.
Quality can be as important as quantity, she suggests.
"Instead of focusing on increasing sexual frequency to the levels they experienced at the beginning of a relationship, couples may want to work on creating an environment that sparks their desire and makes the sex that they do have even more fun," she says.