Married Couples Have Look-alike Immune Systems

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Couple riding on a tandem bicycle
Photo: Erik Isakson

You may have noticed that, as the years go by, married couples start to look alike. Partners who spend a lot of time outdoors have matching tan lines; partners who spend a lot of time indoors have matching Ben-and-Jerry’s bellies. According to a study recently published in the journal Nature Immunology, this look-alike business extends further than you might think, right down to their immunology. 

For their research, scientists from the University of Leuven in Belgium took blood samples from 670 healthy participants, then followed about 150 of them — including about 70 married couples — over the next six months to see how their immune systems responded to the environment. One of the patterns that emerged was the fact that the couples in the study showed very similar immune systems. When the researchers compared the immune system of one person against his or her partner, they found about 50 percent less variation than when they compared a couple of random strangers against one another.

How does that even work? After all, your immune system is a unique chemical autobiography — it is a history of your eating habits, your attempts at exercising, all those random infections and viruses and colds you’ve ever encountered. In fact, your immune system is so unique that only 25 percent of its chemistry can be traced to your genetics.

So this suggests that something is happening when you and your lovebird decide to take the jump and move in together. The lead author told Quartz that while the study didn’t look at unmarried couples, he thinks that they’d probably also be immune-system twinsies. (In a future study, for that matter, researchers want to compare the immunology of couples before and after they begin living together.)

Remember how immune systems tend to reflect your lifestyle habits? Well, your diet and exercise and lifestyle usually coalesce with your live-in partner — you start planning meals together, go to parties together, work out together. You also usually get sick from each other and are in the same environment, which means you’re breathing in pollutants and mold and dust together. All this togetherness in your health habits probably means that it’s not just you and your love moving in together, but your immune systems, too. How romantic!