New York, Feb 17 (IANS): Couples who stay together forever have sex more frequently than those who choose to remarry, a fascinating study shows.

It also revealed that while sexual activity diminishes over time, a slight rebound occurs for those whose marriages endure longer than 50 years.

"Growing old as a couple, with the experience and knowledge that come with that, may play a part," said Samuel Stroope, assistant professor of sociology at Louisiana State University.

You are able to learn about your partner and build on that over time.

You may have a higher level of trust when you feel that your spouse is not going to go anywhere.

"The expectation that the relationship will continue may give you more reason to invest in the relationship - including in sexual aspects of the relationship," he noted.

To reach this conclusion, researchers analysed the relationship between marital characteristics and sexual outcomes among 1,656 married adults aged 57 to 85.

They noted that people who survive until their 50th year of marriage - among whom the slight rebound occurred - are relatively few in number.

The study provided "intriguing results".

While sex becomes less of a novelty over time and frequency tends to diminish, "it may be that the permanency of the relationship contributes to sexual relations picking up a bit at the end", Stroope explained.

As to why "remarrieds" have less frequent sex than those in first marriages, "it may be that those who have been married in the past may not have as strong of a sense of permanence or lasting investment", the authors said.

"We know a great deal about sexual behaviour at younger stages of the life course. This study adds to a small but growing body of research on the sexual behaviour of older adults," added Michael McFarland, assistant professor of sociology and public health at Florida State University.

As people age, they tend to be more even-keeled, which may help cut down on marital conflict and facilitate regular sexual activity into advanced age, the study concluded.

The paper was published in the journal Archives of Sexual Behavior.