Lead author Amy Wachholtz of the University of Massachusetts Medical School and colleagues analyzed data from the Centers for Disease Control and Prevention's 1999, 2002 and 2007 National Health Interview Surveys.
The study primarily focused on comparisons of results between the 2002 and 2007 surveys, which include 30,080 adults from 44,540 households in 2002 and 23,393 adults from 40,377 households in 2007.
People experiencing a decline in health as well as those with improved health reported more prayer, the researchers say.
"The United States did have an increase in worship attendance across multiple religious faiths immediately after the Sept. 11, 2001, attack, but that has not stayed elevated," Wachholtz says in a statement. "However, people continued to use informal and private spiritual practices such as prayer."
Prayer about health issues increased across all groups, from 43 percent in 2002 to 49 percent in 2007, but those in the top income bracket were 15 percent less likely to pray than those with the lowest incomes.
The study, published in the journal Psychology of Religion and Spirituality, finds people who exercised regularly were 25 percent less likely to pray those who didn't exercise, while women, African-Americans and the well-educated were most likely to pray about their health.
"We're seeing a wide variety of prayer use among people with good income and access to medical care," Wachholtz says. "People are not exchanging health insurance for prayer."
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