Think more sex will make you happier?

Despite what many may think, getting a little more active between the sheets isn't a path to more happiness, a new study suggests.

The study from Carnegie Mellon University in Pittsburgh included 128 married, heterosexual couples, aged 35 to 65. All were randomly assigned to either double the amount of sex they had each week or to have their usual amount of sex.

Researchers then tracked the couples' happiness over three months using online questionnaires.

According to the researchers, people who had more sex were not happier than those who had their usual amount of sex. Instead, the study found, the couples who had more sex actually had a small decrease in happiness.

Delving deeper, the team found that one reason why simply having more sex did not make couples happier was because it seemed tied to a drop in their desire for, and enjoyment of, sex.

It wasn't that having more sex led to lower desire and enjoyment of sex, however. Rather, it was because they were asked to do it -- rather than initiating sex on their own, the study authors said.

"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," lead investigator George Loewenstein, a professor of economics and psychology, said in a university news release.

"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 said.

The study was published May 4 in the Journal of Economic Behavior & Organization.

Despite the findings, Loewenstein said he believes couples tend to have too little sex, and that boosting the amount of sex in the right ways can be beneficial.

Study co-author Tamar Krishnamurti also believes the findings might help couples improve their sex lives -- and happiness.

"The desire to have sex decreases much more quickly than the enjoyment of sex once it's been initiated," she explained.

So, "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," said Krishnamurti, who is a research scientist in engineering and public policy at Carnegie Mellon.