Never married adults face higher risk of developing cancer

Adults who have never been married face a significantly higher risk of developing cancer than those who have been married, according to a large U.S. study of more than 4 million cases. The increased risk spans nearly every major cancer type and is especially pronounced for preventable cancers-those linked to infections, smoking and reproductive factors. Led by researchers at Sylvester Comprehensive Cancer Center, part of the University of Miami Miller School of Medicine, the study appears in the April 8 issue of Cancer Research Communications. 

"These findings suggest that social factors such as marital status may serve as important markers of cancer risk at the population level," said Paulo Pinheiro, M.D., Ph.D., study co-author and a Sylvester physician-scientist whose lab conducts population-based cancer epidemiology.

The novel observation does not mean that getting married prevents cancer or that people need to get married.

It means that if you're not married, you should be paying extra attention to cancer risk factors, getting any screenings you may need, and staying up to date on health care."

Frank Penedo, Ph.D., associate director for population sciences and director of the Sylvester Survivorship and Supportive Care Institute (SSCI)

"For prevention efforts, our findings point to the importance of targeting cancer risk awareness and prevention strategies with attention to marital status," he added.

Marriage is already associated with earlier cancer diagnosis and better survival. Married individuals often, but not always, have stronger support systems, greater economic stability and are more likely to adhere to cancer treatment regimens.

But previous work on the links between marriage and cancer focused almost entirely on what happens at and after diagnosis. Only a few small, older studies explored whether marriage affects the odds of getting cancer in the first place.

"We wanted to know who is more likely to get cancer: married people or unmarried people?" Pinheiro said.

To find out, the researchers analyzed a large dataset covering 12 states that included demographic and cancer data from more than 4 million cancer cases in a population of more than 100 million people, collected between 2015 and 2022. They examined cases of malignant cancers diagnosed at age 30 or older and compared rates of various cancers by marital status, further broken down by sex and race and adjusted for age.

The researchers categorized marital status into two groups: those who were or had been married, including married, divorced and widowed individuals, and those who had never been married. The study began in 2015 because that year, the U.S. Supreme Court legalized gay marriage, allowing same-sex couples to be included in the married category. One in five adults in the study had never married.

Pinheiro expected to see some associations, given established relationships between marriage and lifestyle factors such as smoking, routine medical care and having children. But the strength of some findings surprised him.

Adults who were never married had substantially higher rates of developing cancer compared with those who were or had been married. For some cancers, the association was even stronger: adult men who were never married had approximately five times the rate of anal cancer compared with married men. Adult women who were never married had nearly three times the rate of cervical cancer compared with women who were or had been married.

Both anal and cervical cancers are strongly related to HPV infection, so these differences likely reflect variation in exposure, and for cervical cancer, also differences in screening and prevention. In contrast, for cancers such as endometrial and ovarian, differences by marital status may partly reflect the protective effect of parity, which is more common among married individuals.

"It's a clear and powerful signal that some individuals are at a greater risk," Penedo said.

Men and women showed slightly different patterns. Men who were never married were about 70% more likely to develop cancer than married men, while women who never married were about 85% more likely to develop cancer than women who were or had been married.

This represents a small but noteworthy reversal of a broader trend: Men often benefit more from marriage than women in terms of health and social factors. In this case, women appeared to benefit slightly more from marriage than men.

The strongest associations between marriage and cancer were seen for cancers related to infection, smoking or alcohol use, and, for women, cancers related to reproduction, such as ovarian and endometrial cancer.

The researchers found weaker associations for cancers with robust screening programs, including breast, thyroid and prostate cancers.

They also observed patterns across race and marital status. Black men who were never married had the highest overall cancer rates. However, married Black men had lower cancer rates than married White men, indicating a strong protective association with marriage in that group.

The study has limitations. People who smoke less, drink less, take better care of themselves and are more socially integrated may also be more likely to get married.

Still, the researchers found that associations between marriage and cancer were stronger in adults older than 50, suggesting that as people age and accumulate cancer risk exposures, the benefits associated with marriage may become more pronounced.

The study also excluded individuals who are unmarried but in committed partnerships. That group is likely small relative to the size of the dataset, Pinheiro said, but worth exploring in future research.

Future studies could further subdivide the married category into married, divorced and widowed individuals and follow people over decades to better understand how marital transitions affect cancer risk.

Overall, getting married does not magically prevent cancer, both authors stressed.

"But the association between marriage status and cancer risk is an interesting, new observation that deserves more research," Pinheiro said.