Many Americans say they attend church because it helps them stay grounded and gives them spiritual guidance.

A new study suggests that regular attendance may also help increase their lifespan.

Researchers looked at data on nearly 75,000 middle-age female nurses in the United States as part of the Nurses' Health Study. The participants answered questions about whether they attended religious services regularly every four years between 1992 and 2012, and about other aspects of their lives over the years.

The researchers found that women who went to church more than once a week had a 33% lower risk of dying during the study period compared with those who said they never went.

Less-frequent attendance was also associated with a lower risk of death, as women who attended once a week or less than weekly had 26% and 13% lower risk of death, respectively.

Women who regularly attended religious services also had higher rates of social support and optimism, had lower rates of depression and were less likely to smoke.

However, the researchers took into account these differences between churchgoers and non-churchgoers when they calculated the decrease in death rates of 13% to 33%.

Going to church could have a number of additional benefits that could, in turn, improve longevity, but the researchers were not able to examine them with the available data.

Attendance could promote self-discipline and a sense of meaning and purpose in life, or it could provide an experience of the transcendent, said Tyler J. Vander Weele, professor of epidemiology in the Harvard T.H. Chan School of Public Health.

Vander Weele led the new research, which was published Monday in the journal JAMA Internal Medicine.

"Our study suggests that for health, the benefits outweigh the potentially negative effects," such as guilt, anxiety or intolerance, Vander Weele said.

Most of the women in the study were Protestant or Catholic, so it is not clear whether a similar association would be found between religious service attendance and longevity for people of other Christian religions, Judaism or Islam.

The study also did not explore the association in men. Previous research suggests that male churchgoers also benefit, though their decrease in death rate is not as large as among women, VanderWeele said.

"There have been literally thousands of studies" looking at whether religion is good for your health, said Dr. Dan German Blazer II, professor of psychiatry and behavioral sciences at Duke University Medical Center. The findings have been mixed about whether aspects of religious devotion such as prayer and spirituality -- such as reading the Bible or other religious literature -- improve longevity.

"The one (aspect) that is significantly more predictive of good health is about religious service attendance," said Blazer, who wrote an editorial about the new study in the same issue of JAMA Internal Medicine. Most people report that they are spiritual, and it is possible that actually attending religious services is good for their health because they are taking actions that are in line with their beliefs, Blazer said. "You have a more integrated life in this sense."

However, this explanation is purely speculative, and studies have not explored this theory, he added.

The suggestion that attending religious services regularly could boost longevity has met with some criticism in the field.

Other researchers have pointed out that the relationship could be due to other factors, such as the possibility that healthier people are more likely to go to church, perhaps because they are more mobile.

The main strength of the current study is that the researchers were able to look at whether participants reported attending religious services at several points over many years, making it easier to find out which came first, religious activity or disease and health outcomes, Blazer said.

Nevertheless, Blazer warns that it is important not to make too much of the new findings.

"This study does not suggest that clinicians prescribe attending religious services as a way to be healthier," he said. It was not meant to assess going to church as an actual medical intervention.

On the other hand, the study does suggest that "clinicians who know their patients well and follow them over a period of time, like primary care doctors, inquire when it is appropriate about their religious beliefs and practices," Blazer said.

That way, if patients say that attending religious services is important to them, the doctor can help ensure that they maintain a good relationship with their church, temple or mosque.

This attitude about the place of religion in medical care is becoming more common among health care professionals and has been introduced into the curriculum of more and more medical schools, Blazer said.