The marriage vows say "in sickness and in health," but what if it's marriage itself that helps determine whether you're ill or robust?

If you're thinking that a good marriage must be better for your health, it's not that simple. Are you married to a pessimist? Does your beloved nag you to watch your diet? Do you turn sullen when you argue?

All these things — and more — have health repercussions, even for those in decades-long committed relationships.

"In general, yes, a good marriage enhances health, because having someone you love and want to keep around encourages healthy behavior," says Christine Proulx, associate professor of human development and family science at the University of Missouri. Marriage also provides important social support, which could explain why recent studies show that married couples are more likely to survive cancer and less likely to develop dementia or be hospitalized with pneumonia, compared with unmarried adults.

But science has moved beyond simply comparing the benefits of married vs. unmarried. More nuanced studies now suggest the marriage-health connection is different for husbands and wives — sometimes in unexpected ways. "For men, the quality of the marriage seems less important. But only a good marriage is good for a woman's health," says sociologist Hui Liu of Michigan State University.

Here are some of the ways your relationship affects your well-being.

If You've Been Married for Decades

Long-married couples don't just look alike; they can also become biologically similar as they age. Two recent studies found striking similarities in longtime couples, including kidney function, cholesterol, grip strength, difficulty performing daily tasks and depression. Findings presented this year by University of Michigan researchers at the annual meeting of the Gerontological Society of America looked at more than 1,500 older married couples and found that many were in biological sync, based on markers in blood tests. An earlier study by the University of British Columbia and Pennsylvania State University of about 1,700 U.S. couples married more than 40 years found that couples begin to mirror each other's emotional and physical health as they age — an indication of how interdependent, emotionally and physically, long-married couples can become.

If One of You Is Depressed

Your spouse's depression could raise your own risk of chronic pain. A new University of Edinburgh study analyzed more than 100,000 people in the U.K. and found that while chronic pain is caused partly by a person's genetics, a partner's mental health also plays a role. Caring for a depressed spouse could contribute to a mate's pain, researchers said, but there also seem to be environmental factors, such as diet and other habits the couple share.

If You Nag Your Husband

Maybe he should thank you! A nagging wife may actually slow the development of diabetes and promote following doctor's orders in a husband — but, unfortunately, not vice versa. A 2016 Michigan State University study found that a badgering spouse improved a husband's health, even if the constant prodding strained the marital relationship. For men, says sociologist and lead researcher Hui Liu, "nagging is caring." For women, however, nagging is just nagging. Only a good marriage was related to a lower risk of having diabetes in women, Liu says.

If Your Spouse Is An Optimist

Thinking of the glass as half full is better for your health, and so is having an optimistic spouse, says a recent University of Michigan study. The study followed nearly 2,000 older couples for four years. Those couples where one partner had a positive outlook on life experienced fewer chronic illnesses, such as diabetes and arthritis, compared with couples whose partners were not optimistic. They also had better mobility and motor skills over time.

If You Argue a Lot

Every relationship has its spats, but the way you argue with your significant other could make you sick. If loud, angry outbursts are your arguing style, watch out for heart problems and elevated blood pressure down the road. If you tend to silently fume or stonewall your partner during arguments, it could turn into a pain in the neck — literally — or stiff muscles and a bad back, according to new research from the University of California, Berkeley, and Northwestern University.

If Your Significant Other Is an Exerciser

Setting a good example by exercising can influence your mate to follow suit, says recent research from Johns Hopkins University. When a wife began to exercise more, her husband was 70 percent more likely to increase his activity; when a husband started meeting recommended exercise goals, his wife was 40 percent more likely to join in, as well.

If Your Darling Is a Dieter

Perhaps some challenges, like dieting, just shouldn't be done together. That seems to be the lesson from a Colorado State University study of 50 overweight couples. Those who decided to diet together had a rougher time of it, with researchers reporting that one partner's success could derail the other partner, who then became less successful at controlling his or her food portions.

If Your Mate Has Health Challenges

Watch out: One spouse's bad habits can undermine the health of the other. Researchers at McGill University analyzed six international studies involving 75,000 couples and found that the spouses of people with type 2 diabetes had a 26 percent higher risk of developing the disease and also a higher risk for prediabetes — possibly because of shared bad habits like poor diet and not enough exercise. The results, say researchers, should encourage doctors who diagnose one spouse with diabetes to also ask about the health habits of the other spouse.

If You Play the Role of Caregiver

It's not surprising that the stress of a health crisis or significant chronic health issue in one partner will affect the health of the other, says psychologist Cheryl Rampage of Northwestern University's Family Institute, but a recent study found that a stroke had particularly long-lasting effects. The impact of caring for a stroke survivor can affect the mental and physical health of the caregiver spouse not only during the first years but up to seven years afterward, Swedish researchers reported.