Praying for the health of strangers who have undergone heart surgery has no effect, according to the largest scientific study ever commissioned to calculate the healing power of prayer.

In fact, patients who know they are being prayed for suffer a noticeably higher rate of complications, according to the study, which monitored the recovery of 1,800 patients after heart bypass surgery in the US.

The findings of the decade-long study were due to be published in the American Heart Journal next week, but the journal published the report on its website yesterday as anticipation grew.

The power of intercessory prayer has been studied by doctors for years in America, but with no conclusive results. This $2.4 million study, funded in large part by the John Templeton Foundation, which seeks "insights at the boundary between theology and science", was intended to cast some clear light on the matter.

But the study "did not move us forward or backward" in understanding the effects of prayer, admitted Dr Charles Bethea, one of the co-authors and a cardiologist at the Integris Baptist Medical Center in Oklahoma City. "Intercessory prayer under our restricted format had a neutral effect," he said.

Members of three congregations - St. Paul's Monastery in St. Paul; the Community of Teresian Carmelites in Worcester, Massachussetts; and Silent Unity, a Missouri prayer ministry near Kansas City - were asked to pray for the patients, who were divided into three groups: those who would be told they were being prayed for, those who would receive prayers but not know, and those who would not be prayed for at all.

The worshippers starting praying for the patients the night before surgery and for the next two weeks, asking God to grant "a successful surgery with a quick, healthy recovery and no complications".

The study found no appreciable difference between the health of those who did not know they were being prayed for and those who received no prayers. Fifty-two per cent of patients in both groups suffered complications after surgery. But 59 per cent of those who knew they were prayed for went on to develop complications.

The reports authors said they had no explanation for the difference beyond a possibility that the prayers made people anxious about their ability to recover.

"Did the patients think, ’I am so sick that they had to call in the prayer team?"’ said Dr Bethea.

The results of the study provoked discord among doctors and scientists in the US, many of whom questioned the wisdom of subjecting prayer to the conditions of a research project.

Dr Richard Sloan, a professor of behavioral medicine at Columbia and the author of a forthcoming book, Blind Faith: The Unholy Alliance of Religion and Medicine, told The New York Times: "The problem with studying religion scientifically is that you do violence to the phenomenon by reducing it to basic elements that can be quantified, and that makes for bad science and bad religion."

But Paul Kurtz, Professor Emeritus of Philosophy at the State University of New York at Buffalo, and chairman of the Committee for the Scientific Investigation of Claims of the Paranormal, had a simpler response when asked why the study had found no evidence for the power of prayer. "Because there is none," he said. "That would be one answer."

Dr. David Stevens, executive director of the Christian Medical and Dental Associations, told the AP that he believed intercessory prayer could influence people's health, but that scientists were not equipped to measure the phenomenon.

"Do we control God through prayer? Theologians would say absolutely not. God decides sometimes to intervene, and sometimes not," he said. As for the new study, he said, "I don’t think... it’s going to stop people praying for the sick."

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