Women who attend religious services frequently may live longer than women who don't, new research suggests.

Over the 16-year study, religious service attendance was linked to a substantial reduction in mortality, Tyler J. VanderWeele, of the Harvard T.H. Chan School of Public Health, Boston, told Reuters Health by email.

VanderWeele and colleagues analyzed data collected every four years between 1996 and 2012 from nearly 75,000 women participating in the Nurses' Health Study. Most were Catholic or Protestant.

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As reported in JAMA Internal Medicine, about 14,000 of the women attended religious services more than once a week, about 30,400 attended once a week, about 12,000 less than once a week, and nearly 18,000 never attended.

Women who attended religious services regularly were 33 percent less likely to die during the study period, compared with women who never attended services. Once-a-week attendees were 26 percent less likely to die, and those attending less than once a week were 23 percent less likely to die.

Overall, frequent religious attendance was associated with a 27 percent lower likelihood of dying from cardiovascular disease and a 21 percent lower risk of death from cancer. Frequent attendance was also associated with significantly less risk of breast cancer and colorectal cancer.

"Although attendance at religious services was associated with lower cardiovascular mortality and cancer mortality, attendance was not significantly associated with incidence of breast cancer or cardiovascular disease," the researchers wrote.

So-called observational studies like this one can't prove cause and effect, VanderWeele said. But, he added, "That we had data on both service attendance and health repeatedly over time helps provide evidence about the direction of causality."

Dr. Dan German Blazer, of Duke University Medical Center in Durham, North Carolina, who wrote an accompanying commentary, told Reuters Health by email, "Though we do not know the mechanisms, research and especially this study, emphasize the importance of religious service attendance to health.

Because the study only included middle-aged and older professional women, "we do not know whether the results would hold for men or for younger persons," Blazer said. "We need to continue to chip away at a better empirical understanding of cause and effect and refrain from either over-generalizing these results or dismissing them as impossible to better understand.