People are most likely to commit suicide in the middle of the week, according to a new American study.

Researchers at the University of California, Riverside, say Wednesdays see the highest rates of self-inflicted death, not Mondays as past research has indicated. The study appears in this month's issue of the journal Social Psychiatry and Psychiatric Epidemiology.

"As far as I know, this study is first to demonstrate that there has been a shift," says lead researcher Augustine Kposowa, a professor of sociology.

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Using data from the U.S. Multiple Cause of Death Files, Dr. Kposowa and graduate student Stephanie D'Auria examined suicides that occurred between 2000 and 2004 in all 50 states. During that study period, Wednesdays proved deadliest, with 25 per cent of suicides.

Mondays and Saturdays followed, with 14 per cent of suicides each; Thursdays and Fridays showed the lowest rates, with 11 per cent of suicides occurring on either of those days.

Mondays have long been identified as the worst day of the week, both in academic research and popular culture. The day was linked with suicide as long ago as the 19th century, when Emile Durkheim, one of the pioneers of sociology, theorized that suicides were most likely at the beginnings of new periods or phases.

But Dr. Kposowa says Wednesdays have become the darkest days of the 21st century because of increased workplace pressures.

Competition has also become too extreme, and most people no longer derive pleasure from their career, he says. "Hump day," as Wednesday is known, is difficult because the previous weekend has already become the distant past, while the upcoming weekend is still far away.

"There are too many stressors," Dr. Kposowa says. "These uncertainties and stressors become more pronounced in the middle of the week."

Another surprising finding was that suicide rates were highest during the warmer months - not winter, another common belief. August, June and April showed the highest rates, with 26 per cent of suicides occurring during the summer, compared with 24 per cent in the winter.

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One possible explanation is "relative deprivation," Dr. Kposowa says. In the summer, the majority of people become more visibly active, taking vacations, gardening or renovating their homes. This might cause some individuals to feel such joys are missing from their own lives.

But Dr. Kposawa says a more intriguing possibility is that the proliferation of communication technologies has made it easier for people to reach out when they are suffering from winter blues.

Dr. Kposawa says his research indicates a need to reduce stress in the workplace. He also suggests crisis prevention centres increase staffing in the middle of the week.

Karen Letofsky, executive director of Distress Centres of Toronto, says her crisis hotlines are busiest during the first half of the work week, although she can't pinpoint a particular day that spikes above the others.

"Suicide is incredibly complex, and we know that it could happen at any … time," she says. "[The study]wouldn't mean we'd be more vigilant on Wednesday versus Monday. It would mean that we would always be vigilant."