"Worried About Cancer? Get Married"
Controlling for demographic factors such as age, race, education and household income, researchers who analyzed records of more than 730,000 cancer patients found that married patients did significantly better than single people. They lived longer, received better treatment and were more likely to be diagnosed before metastatic cancers developed.
It didn’t matter whether the unmarried patients were lifelong singles, divorced, widowed or separated. All did worse than demographically similar married patients.
I'd suspect a selection effect also plays a role. But, presumably, the comparison to widowed folks controls for that.