Earn more money, when you have more sex, study says (seriously!)

Izabela Habur | E+ | Getty Images

Now we know how "Sex and the City's" Carrie Bradshaw could afford a closet full of designer shoes as a freelance writer: A new study finds that sexually active people make more money.

And if you do it more than four times a week, you earn even more, the study shows.

"There is a monotonic relationship between the frequency of sexual activity and wage returns," Nick Drydakis, a senior economics lecturer at Anglia Ruskin University in England wrote in a paper for the International Journal of Manpower.

When people are having sex regularly, they're happier, stronger, eat better and exercise more, researchers have found. Drydakis called sexual activity a "barometer" for several characteristics an employer would want in a worker or traits that could make someone a better worker.

"Being sexually active is a proxy for good health, and that itself is correlated with having higher energy for everything, including work," Andrew Oswald, economics professor at Britain's Warwick University, said via email.

"Physical and mental health, as well as personality characteristics, are important factors that affect wages. The patterns found in this study strengthen this reasoning," Drydakis wrote.

The "Sex and the City" bed-hopping cliché notwithstanding, marriage seems to have a lot to do with it. "Married people, particularly men, earn higher wages than the non-married," Oswald said. "One possible explanation is that such people are sociable, stable people."

(Read more: Would you give up sex to avoid paying bills?)

Conversely, a sexless marriage appears to be detrimental to a person's earning power. "Married men having no sex receive lower wages by 1.3 percent," Drydakis wrote, calling the amount "statistically significant."

Drydakis did have one caveat, which we'll call the gold-digger variable: In some cases, a better job or higher income could be the reason someone starts having more sex, rather than the other way around.

"Higher wages may increase the value and attractiveness of a person on the dating market; higher wages may also increase purchase of gifts that are thanked for via sex," the paper pointed out.

However, a 2004 paper published in the Scandinavian Journal of Economics written by Oswald and Dartmouth College professor David Blanchflower found, "Higher income does not buy more sex or more sexual partners."

Drydakis noted sex is a relatively fundamental need based on psychologist Abraham Maslow's hierarchy of needs, along with food and shelter.

(Read more: Sex sells, but not always)

"If basic needs are not satisfied, human beings cannot function. People need to love and be loved," he wrote. "In the absence of these elements, many people become susceptible to loneliness, social anxiety, and depression that could affect their working life."

According to Warwick University's Oswald, "Happiness does raise productivity in humans," so it's possible that people who are having sex are more productive at work because they're in a better mood—albeit maybe a bit sleep-deprived. Drydakis found that people having sex more than four times a week see the biggest wage benefit.

—Martha White, NBC News