Can your relationship status make a difference in your overall well-being? To borrow a commonly used Facebook phrase, it’s complicated. Research shows that strong partnerships can help us avoid illness, adopt healthier habits, and even live longer. On the other hand, troubled relationships tend to breed stress and weaken immunity.Weight gainIt’s a common belief that couples "let themselves go” after pairing off, and there may be something to it. According to a 2012 review, people tend to gain weight as they settle into marriage and lose weight when a marriage ends.But Troiani has seen the opposite happen quite often, as well: "A happy couple can motivate each other to stay healthy—they’ll go to the gym together, set goals, and feel responsible for each other.” When couples do pack on the pounds, she adds, it may be a symptom of conflict, not slacking off. "Dissatisfaction in the relationship can lead to passive-aggressive eating behaviors and sleep problems, which will lead to weight gain,” she says.Stress levelsSurprise, surprise: Regular physical intimacy appears to reduce stress and boost well-being. One study, published in 2009 in the Journal of Sexual Medicine, found that people who frequently had sex were healthier mentally and more likely to report greater satisfaction with their relationship and life overall.Sex is just one aspect of a relationship, however. And your partner’s behavior outside the bedroom can just as easily send stress levels soaring in the opposite direction. Parenting disputes, disagreements over money, or even questions as simple as who does which household chores have been shown to increase stress.Feel-good hormonesSex isn’t the only type of physical contact that can lower stress and improve health. In a 2004 study of 38 couples, University of North Carolina researchers found that both men and women had higher blood levels of oxytocin—a hormone believed to ease stress and improve mood—after hugging. The women also had lower blood pressure post-hug, and lower levels of the stress hormone cortisol.Sleep problemsSleeping next to someone you love and trust can help you fully relax and embrace sleep, Troiani says. A big exception to that rule, of course, is if your bedmate keeps you up at night—by snoring, for instance, or by tossing and turning. In a 2005 poll , people were more likely to experience daytime fatigue and fitful sleep themselves if their partner was struggling with insomnia.Relationships can affect sleep in less direct ways, too. Research shows that relationship insecurity or conflict is associated with poorer sleep—and to make matters worse, sleep problems can exacerbate relationship problems, creating a vicious cycle.AnxietyRelationship difficulties can put anyone on edge, but in some cases they may actually contribute to full-blown anxiety. Several studies have found a link between marital problems and an increased risk of diagnoses such as generalized anxiety disorder and social anxiety.These links can be difficult to untangle, however, since anxiety has been shown to breed relationship problems (and not just vice versa). What’s more, some research suggests marriage may help protect against anxiety. In a 2010 World Health Organization study  of 35,000 people in 15 countries, those who were married—happily or otherwise (the study didn’t specify)—were less likely to develop anxiety and other mental disorders.DepressionDepression and anxiety often go hand in hand, so it makes sense that relationships can affect depression in similarly complex ways. On the one hand, some studies  have found that long-term relationships—and marriage, specifically—can ease symptoms in people with a history of depression.On the other hand, fraught relationships have been shown to dramatically increase the risk of clinical depression. In one small but highly cited study , women—regardless of their personal and family history of depression—were six times more likely to be clinically depressed if their husbands had been unfaithful or if their marriages were breaking apart.Alcohol useOur romantic partners have a noticeable impact on how much alcohol we consume, and how often. One study , which followed more than 600 couples during their first four years of marriage, found that people’s drinking habits tended to mirror those of their spouse; if their partner drank heavily, they too were more likely to do so.It’s also true that relationship conflict and a lack of intimacy can drive people to drink. Research suggests  that both men and women drink more in response to relationship problems—and excessive drinking, in turn, can add fuel to those problems.Attention to healthAlthough it might seem like pestering at times, a partner’s watchful eye and day-to-day care—whether it’s pointing out worrisome symptoms, or checking that you’ve taken your medicine—seem to foster a healthier lifestyle and closer attention to health problems. Case in point: A 2011 Canadian study found that married men experiencing chest pains tend to get to the hospital sooner than single ones, regardless of whether their wives were even home at the time."People in healthy relationships really do take care of each other,” Troiani says, "and they may even feel more of an obligation to take care of themselves, too.”HeartacheIt’s not just your current relationships that can affect health, but your past ones, as well—especially those that ended in hurt feelings and rejection. In 2011, researchers from Columbia University found that thinking about an ex-lover can have similar effects on the brain as physical pain.It’s even possible for a breakup to result in something called broken heart syndrome, a temporary enlargement of the heart (with symptoms mimicking a heart attack) brought on by extreme physical or emotional stress. Postmenopausal women are most likely to experience the syndrome, but research shows that it can also occur in men and younger women, as well.