A new study suggests that middle-aged people with surgically confirmed endometriosis have a slightly lower mortality rate than their peers who don’t have endometriosis. The reasons for this aren’t totally clear, but researchers suggest they are likely related to differences in lifestyle and medical attention and care.

The study, “Mortality of midlife women with surgically verified endometriosis — a cohort study including 2.5 million person-years of observation,” was published in the journal Human Reproduction.

Endometriosis has been linked to an increased risk of life-threatening diseases, including heart disease and cancer. As such, one might assume that people with endometriosis have a higher mortality rate (a greater likelihood of death from any cause). However, there isn’t much data directly assessing this.

Thus, researchers used a combination of national databases from Finland to obtain information on 49,956 people with endometriosis verified through surgery. The patient data covered 1987 to 2012; the average patient age was 36.4 years at the beginning of follow-up and 53.6 years at the end of follow-up.

Data for a control (without endometriosis) cohort of 98,824 age-matched individuals was also obtained. In total, the study accounted for 2.5 million person-years’ worth of data.

The overall mortality rate was slightly, but significantly, lower in the endometriosis cohort than in the control cohort: 19.6 versus 25.9 per 1,000 people over 10 years.

This included 12% fewer deaths from cancer and 45% fewer deaths from heart disease in the endometriosis cohort. Deaths related to alcohol, violence, and respiratory and digestive diseases were also less common in the endometriosis cohort, but rates of death from nervous system diseases such as Alzheimer’s were similar in both groups, as were rates of suicide.

“We speculate that the decreased mortality is significantly due to different characteristics and factors related to women’s lifestyle and/or increased medical attention and care received among women with surgically verified endometriosis,” the researchers stated in their paper. They stressed, however, that this was strictly speculation; a major limitation of this study is that data on lifestyle factors that also greatly affect diseases such as cancer (e.g. smoking) were not included in the analysis.

The researchers also noted that “the present results can be applied only to midlife women with surgically verified endometriosis, and caution is needed when interpreting the results in terms of causality.” In other words, this paper only shows that two things are associated; it makes no claim that having endometriosis has a direct effect of decreasing the chance of death — and this paper only applies to a particular population of a particular age. “There is a need for more studies on this issue,” the researchers concluded.