Attending religious services at least once a week may offer spiritual and social protection against suicide, a large U.S. study suggests.

Among nearly 90,000 women followed for over a decade in the Nurses' Health Study, those with regular religious attendance had a five-fold lower risk of suicide compared to women who didn't go to services.

"There was also some evidence that this varied by religious affiliation: Protestant women who attended services once or more per week were approximately 3 times less likely to subsequently commit suicide, whereas Catholic women who attended services once or more per week were about 20 times less likely to commit suicide," lead author Tyler J. VanderWeele said by email.

"These are very large effect estimates," said VanderWeele, of the Harvard T.H. Chan School of Public Health in Boston.

The researchers analyzed data on female nurses who were recruited starting in 1976 when they were 30 to 55 years old and who answered extensive lifestyle questionnaires every two years. Focusing on the period between 1996 and 2010, the study team followed 89,708 participants.

Among women with a religious affiliation, most were Protestant or Catholic, and about 2,000 identified as Jewish, Buddhist, Hindu or "other."

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Of all the women followed, 17,000 said they attended religious services more than once a week, 36,000 went once weekly, 14,000 went less than once per week and 22,000 never attended.

By 2010, 36 women had committed suicide according to the results in JAMA Psychiatry. Compared to women who didn't attend services, those who went once a week or more had just 16 percent of the risk.

The researchers found that differences in alcohol intake, depression and social integration accounted for some of the difference in suicide risk between women who never went to services and those who attended regularly. But it didn't explain the entire risk difference.

"Those who attended religious services tended to subsequently have more social support, were less depressed, and consumed less alcohol," VanderWeele told Reuters Health.

"Our speculation is that an important mechanism relating religious service attendance and lower suicide risk might be the belief that suicide is morally wrong, but this would require other studies that assessed such moral beliefs," he said. "Feeling close to God has also been proposed as a mechanism that may prevent suicide but this too would require future research to assess."

There's strong evidence that this is a causal relationship, with attending religious services causing a reduction in suicide risk, but with this kind of observational data it's not possible to say for sure, he said.

The results may vary by religious group as well, and there were no men included in the Nurses' Health Study, VanderWeele noted.

Suicide is much less common for women than for men, said Dr. Harold G. Koenig of Duke University Medical Center in Durham, North Carolina, who wrote an editorial accompanying the study.

"In most Christian religious like Catholicism and Protestantism, you are not supposed to kill yourself," Koenig said.

"Actually as a psychiatrist I find that helpful in many respects," he added.

If providers take a "spiritual history" of their patients with depression, it may help identify strategies to reduce suicide risk Koenig told Reuters Health.

"We support a patient's resources, and one resource may be a person's faith community if they are already involved or were involved," he said.

"Decisions about religious practice and formation of religious beliefs are of course not made on grounds of health or suicide prevention, but rather reflect values, relationships, experiences, evidence, thought, upbringing and so on," VanderWeele said. "However, for those who already hold religious beliefs, but do not attend services, the study does question whether they are perhaps missing something of the communal religious experience that is powerful."

Suicide is one of the 10 leading causes of death in the U.S. Psychiatrists, clinicians and healthcare providers should at least be aware that there may be a relationship between religious services and suicide risk, VanderWeele said.