Researchers turned to the English Longitudinal Study of Ageing and examined the physical activity and smoking habits, as well as weight-loss patterns, of 3,722 married and cohabiting English couples who are at least 50 years old.
Across those measures, being with somebody who worked to reduce their unhealthy habits gave adults better odds of improving their own health. Among smokers, just 8 percent of those partnered up with smokers quit the habit. But that number jumped to nearly 50 percent when smokers' partners also quit.
A similar pattern emerged regarding exercising; physical activity increased for about 70 percent of both men and women when their partners did the same. But just about a quarter of men and women with non-active partners increased their physical activity.
As for losing weight, the researchers looked specifically at whether people lost 5 percent of their body weight. A quarter of men with partners who lost weight also dropped pounds, while 10 percent lost weight when their partners didn't. For women, 36 percent lost weight when with someone who did the same, while just 15 percent of women lost weight when their partners didn't.
While the researchers didn't zero in on why this pattern emerged, senior author Jane Wardle of University College London told Reuters it may have to do with mutual support and even competition.
But they did find that changes weren't as dramatic for those coupled up with already healthy people, rather than with people who also worked to change habits. Still, the researchers did find that merely being with a physically active person or a non-smoker did influence partner behavior.
"Men and women are more likely to make a positive health behavior change if their partner does too, and with a stronger effect than if the partner had been consistently healthy in that domain," the authors write. "Involving partners in behavior change interventions may therefore help improve outcomes."
Weight-loss was a bit different; the chances that overweight adults would lose weight didn't increase if their partners were already a healthy weight.
"The partner merely being slim didn’t seem to promote change," Wardle told Reuters. "Perhaps couples can more easily ignore (or accept) differences in weight without feeling any pressure to change; perhaps weight differences aren’t as readily expressed as visible differences in food intake."