Romantic partners can share many things, like an interest in pets, watching movies for hours and good meals. Married couples or cohabitating couples have more to share because they live under the same roof. They sleep in the same bed, eat the same meals and keep their toiletries in one place.

So much togetherness can bring about a problem, though, as some unhealthy habits turn into shared unhealthy habits -- like smoking or turning into a couch potato. When couples have similar unhealthy habits, their risk of heart disease may increase, according to a recent study.

The Study

Investigators from Brigham and Women’s Hospital in Boston and Quest Diagnostics examined if unhealthy habits shared by 5,000 couples might affect their heart health. The couples were members of an employee wellness program offered by Quest.

They focused on cardiovascular risk factors, those related to the heart and blood vessels. The researchers used the American Heart Association’s Life's Simple 7 (LS7) risk factors and behaviors to define the habits, which included smoking status, body mass index (BMI), physical exercise, diet, blood pressure, blood cholesterol and blood sugar. Participants answered questionnaires and underwent examinations and laboratory tests.

The team found that, as individuals, more than 50% of participants were on the ideal side of three LS7 measures. They had never smoked and had good cholesterol and blood sugar levels. But more than 25% scored poorly for BMI, physical activity and cardiovascular health, while only 12% scored ideally for cardiovascular health. The low scores on the LS7 were mostly connected to an unhealthy diet and lack of physical exercise.

The couples as a whole

When couples were considered together, they often shared several parts of the LS7. Over 50% of the couples had similar risk factors and behaviors across LS7, as well cardiovascular health scores.

When investigators checked how many couples were on the non-ideal side, 79% were in the non-ideal category for cardiovascular health. The situation was also linked to the couples' lack of physical exercise and poor food choices. So, if they exercised more and had a proper diet, they likely had positive scores.

There were some interesting insights into the power of habits among the couples. When one person decided to stop smoking, lose some weight and change diet, the partner would follow the trend. This suggests one partner’s ability to improve might motivate the other to do the same. However, in the more than five years of the study, the risk factors and behaviors of participants were generally unchanged.

"Our analysis demonstrates the power of intimate relationships to influence an individual's long-term health risks," said Dov Shiffman, PhD, in a press release from Brigham and Women's Hospital. Dr. Shiffman is senior fellow and scientist for Quest Diagnostics.

Couples Influencing Each Other

A different study published in the Annual Review of Clinical Psychology and conducted at Ohio State University, showed what may influence couples throughout their life together. The biggest factor is interconnectedness. The deeper the connection is, the greater the influence between members. This may affect both positive and negative factors between them.

Depression, for example, may exist or persist due to interconnectedness. Therapists may see an opportunity here: If they treat one partner who improves, it might encourage the other to try therapy.

Diet, as mentioned before, is also a shared factor for most couples. A tight budget may lead couples to eat unhealthy foods like processed or canned goods and cheap fast food. If they have access to better income, they may improve their diet.

If couples recognize the role they each play in their relationship in terms of healthy or non-healthy habits, they can work together – or with a therapist – to adopt a healthier lifestyle, so they can age together in better health.

Ralph Chen is an enthusiast of medical topics and advanced technologies. When not writing, he spends time playing popular PC games.