Having sex on the first date may harm relationships over the long-term, a new study suggests.

The study included nearly 11,000 unmarried people in steady or serious relationships who rated their level of satisfaction with their relationship, their ability to communicate with their partner and the stability of their relationship (how often they thought  the relationship was in trouble).

Among couples who had been together for at least one year, those who had engaged in sex before or within the first few weeks of dating had lower levels of relationship satisfaction, communication and stability compared with couples who waited longer to have sex or who abstained from sex.

The results held even after researchers took into account factors that could have affected the findings, such as race, education, number of sexual partners and religious attendance.

The findings agree with earlier work in married couples that found that the longer couples waited to have sex before marriage, the higher their martial satisfaction, the researchers said.

It's not clear why delaying sex was linked to better relationship outcomes. It could be that couples who engage in sex early have high expectations for the frequency of sex and their partners' interest in sex later on — factors that tend to decline over time.

“The eventual mismatch between individual sexual expectations and actual rewards may undermine healthy couple formation processes,” the researchers wrote in the Nov. 2 issue of the Journal of Sex Research.

However, some experts are critical of the study's conclusions. While the effect the timing of sex had on relationships was real, it was small, leading some to question whether or not it could really make a difference in the real world.

“The overall difference in satisfaction and communication scores between those who had early sex and those who waited was one-tenth of one point on a five-point scale,” said Justin Lehmiller, a social psychologist at Harvard University, who studies relationships and was not involved in the current study. “Does one-tenth of one point really mean having sex on the first date will kill your relationship? No, and it would be disingenuous to suggest that based upon these results,” Lehmiller added.

In addition, the study did not follow the same couples over a long time period. Rather, it included information from just one point in time. This means the researchers can't say what caused the association.

“It may have nothing to do with sex,” Lehmiller said. “Perhaps there are personality differences between those who jump into bed and those who wait that could explain the association.”

The researchers, from Brigham Young University's School of Family Life, acknowledge that other factors, including family background and attitudes toward relationships, likely influence when people decide to first have sex, and future studies should examine how these factors affect the relationship over time.

Pass it on: Having sex early in a relationship may have a harmful, yet small effect on the relationship down the road.

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