(Reuters Health) - People who have had 10 or more sexual partners during their lifetime may have increased odds of being diagnosed with cancer, a new study suggests.

Women, in particular, had nearly twice the risk when they had 10 or more past partners compared to when they had one or none, researchers report in BMJ Sexual & Reproductive Health.

While the study team expected to find an association between number of sexual partners and cancer, they were surprised to find a gender difference.

“Previous research has shown that specific STIs (sexually transmitted infections) may lead to several cancers,” said study coauthor Lee Smith, a reader at the Anglia Ruskin University in Cambridge, UK.

“It is interesting the risk is higher in women when compared to men,” Smith said in an email. “This may be because the link between certain STIs and cancer is stronger in women.”

To look at how the number of sexual partners might impact health, Smith and colleagues turned to data from the English Longitudinal Study of Aging, a nationally representative study of adults aged 50 and older.

They focused on data from 5,722 men and women, average age 64, who were asked in 2012-2013 to report their lifetime number of sexual partners. Participants were also asked about their health and about any longstanding condition or infirmity that affected their routine activities.

Among men, 29% reported one or zero sexual partners, 29% had two to four, 20% had five to nine and 22% reported having 10 or more. Among women, just under 41% had one or zero sexual partners, 36% reported two to four partners, 16% reported five to nine partners and 8% said they had 10 or more.

Women and men with higher numbers of partners tended to be younger, unmarried and more likely to smoke and drink alcohol frequently. They were also more likely to do some kind of vigorous exercise weekly and to be on either the high or low end of the wealth spectrum, the researchers note.

Compared to women who reported one partner or none, those who reported 10 or more were 91% more likely to have been diagnosed with cancer. Similarly, men with 10 or more partners were 64% more likely to have been diagnosed with cancer compared to men with one partner or none.

In addition, women with 10 or more partners were 64% more likely than those with the fewest to report having a limiting, long-standing illness.

But there were no differences among women or men in self-rated health, or heart disease or stroke, based on number of lifetime sexual partners.

These findings should be interpreted very cautiously, said Dr. Konstantin Zakashansky, an associate professor of gynecologic oncology at the Icahn School of Medicine at Mount Sinai in New York City.

The study can only show an association, not prove cause and effect, Zakashansky said. Further, it did not specify which cancers were diagnosed and the data depended on people’s self-reports.

The associations in the study may just be a marker for other lifestyle issues, since people who had more partners were also more likely to smoke and drink, said Dr. Robert Edwards, a professor of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh School of Medicine.

Moreover, Edwards said, “smoking and alcohol consumption amplify the risk for cancer with certain sexually transmitted diseases.”

Smith had advice for those with very active sex lives: “People who had risky sexual encounters should contact their health care providers to get checked for potential sexually transmitted infections and should discuss openly how to minimize this risk with their health care providers. Using appropriate protection will reduce the risk of related cancers going forward.”

SOURCE: bit.ly/2URl7Zo BMJ Sexual & Reproductive Health, online February 13, 2020.