A recent study to be published in the Journal of Sex Research later this month confirms what many people in happy relationships probably already know: The two keys to long-lasting happiness are communication and sex. 

Researchers at Chapman University surveyed 39,000 heterosexual couples who had been living together or married for at least three years or more and asked them to rate both their sexual satisfaction within the first six months of their relationship and their current level of sexual satisfaction. They found that while 83 percent of couples said they were very satisfied with their sex life at the beginning of their relationship, only half said they were currently satisfied with their sexual relationship. 

This next finding probably won't surprise you: Couples who said they were currently satisfied with their sexual relationship have more sex than their unsatisfied counterparts, with 79 percent of men and 81 percent of women who are sexually satisfied reporting that they have sex at least once a week. 

That said, researchers aren't entirely sure whether happy relationships lead to more sex or more sex leads to happier relationships. Regardless, sexually satisfied couples have another thing in common: They communicate, whether that's asking their partner for what he or she wants in bed, asking for something themselves, praising their partner for something he or she did in bed, or simply telling each other, "I love you."

Moral of this story? Whether you're coupled up or not, don't be afraid to speak up about what you want in bed or out of a relationship. 

Read more about the study over at the Wall Street Journal