Older married couples with the same drinking habits - whether they partake, or abstain - tend to be happier than couples where only one partner drinks, researchers say.

Based on data for a nationally representative sample of U.S. couples over age 50, the study found that women, in particular, were more dissatisfied over time when only they, and not their husband, drank.

The amount that people drank was less important than whether both partners had the same habit of drinking or not drinking, researchers report in Journals of Gerontology B: Psychological Sciences, online June 27.

"We're not suggesting that people should drink more or change the way they drink, said study author Dr. Kira Birditt of the University of Michigan in Ann Arbor, who studies relationships across adulthood.

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"We're not sure why this is happening," she told Reuters Health, "but it could be that couples that do more leisure time activities together have better marital quality."

In other words, drinking may not be the only reason they're getting along, Birditt said.

For the study, Birditt and her colleagues analyzed responses from 4,864 married participants, in 2,767 couples, participating in the long-term Health and Retirement Survey. Between 2006 and 2016, all participants had a face to face interview with researchers and answered questionnaires about their drinking habits - whether they drank, how many days a week they drank and how many drinks they had on the days they drank.

Couples were married for an average of 33 years and about two-thirds were in their first marriage.

They also answered questions about the quality of their marriage, including whether they thought their spouses were too demanding or too critical, if their spouse was reliable when they needed help and if they found their spouse irritating.

Results showed that in more than half of couples, both spouses drank. Husbands were more likely to drink than wives. But particularly for wives, there was a problem when only one of the spouses drank.

When wives drank and the husbands didn't, wives reported they were more dissatisfied with their marriage.

"The study shows that it's not about how much they're drinking, it's about whether they drink at all," Birditt said.

But, she emphasized, drinking among older adults is becoming an increasing problem, "especially among baby boomers, who seem more accepting of alcohol use."

It also shows that partners influence each other in a relationship, she added.

Birditt speculates that spouses have a huge impact on each other, especially when they're older and retired and spending a lot of time together. She suggests that when one spouse has to stop drinking, the other should stop as well.

Another intriguing finding was the number of people in the study who were heavy drinkers, noted Dr. Fred Blow, also at the University of Michigan, who was not involved with the study.

About 20 percent of men and 6 percent of women had significant drinking problems in this study, he said.

"Problem drinkers are a whole different kettle of fish," he said. "Serious heavy drinkers have disruptive relationships with people, particularly their partners. That's an important issue that should be looked at going forward."