Though countless married people no doubt live miserable lives, new research suggests an optimistic spouse is the key to happiness.

In analyzing data on 1,970 heterosexual couples in the United States, psychologists from the University of Michigan found that those who had an “optimistic spouse” enjoyed better mobility and fewer chronic illnesses than others. Most important, the researchers stressed that they’d isolated the effects of spousal optimism from one’s own sense of optimism. The study was published this week in the Journal of Psychosomatic Research.

“A growing body of research shows that the people in our social networks can have a profound influence on our health and well-being,” study leader Eric Kim said in a press release. “This is the first study to show that someone else’s optimism could be impacting your own health.”

Yet the psychologist also said the association doesn’t necessarily prove a causal relationship between spousal optimism and improved health.

“Practically speaking, I can imagine an optimistic spouse encouraging his or her partner to go to the gym, or eat a healthier meal because the spouse genuinely believes the behavior will make a difference in health,” Kim said. “Identifying factors that protect against declining health is important for the increasing number of older adults who face the dual threat of declining health and rising health care cost.”

Kim and his colleagues tapped data from a longitudinal study of U.S. adults over age 50, whom they tracked for several years to measure outcomes including physical functioning, self-rated health, and prevalence of chronic illnesses. They then analyzed the data on the couples using the actor-partner interdependence model commonly used for such psychological studies.

Among other findings, the researchers found that optimism in general is associated with myriad health benefits for the individual, while a spouse’s optimism may also affect one’s health over time. Researchers from the University of Rochester found in a 2010 literature review on the subject a ringing consensus: Optimism improves health. Past work has found that optimism positively affects longevity, disease survivability, cardiovascular health, cancer outcomes, and pain tolerance, among other measures.

Interestingly, those researchers noted the positive effects of optimism were realized by people throughout society, including those among the lower socioeconomic classes.

Source: Kim, Eric S., Chopik, William J., Smith, Jacqui. Are people healthier if their partners are more optimistic? The dyadic effect of optimism on health among older adults. Journal of Psychosomatic Research. 2014.