A bar on a street in Qingdao, Shandong province, creates an atmosphere of the ongoing soccer World Cup to attract enthusiasts. [Photo by Wang Haibin / For China Daily]

The once-in-four-years soccer World Cup is here and fans in China are thrilled, but the 11-hour time difference between China and Brazil, the tournament's host this year, is spoiling some of the fun.

Although millions of soccer-crazy Chinese people are staying up night after night to watch as many matches as they can in the monthlong affair, reports of health problems triggered by sleep deprivation are also trickling in.

At least five people have died of strokes and heart attacks, after watching games continuously at nights, according to media reports from Shanghai, and Jiangsu and Guangdong provinces.

Now, doctors are asking soccer fans to take it easy.

"From a doctor's perspective, it is wise to sacrifice one's sleep and health only to a reasonable extent, because otherwise, the effects might be deadly," says Guo Lijun, a senior cardiologist with the Peking University Third Hospital. Guo says he gets the whole frenzy but cautions against medical risks.

Studies have shown that sleep deprivation is associated with increased incidence of strokes and heart attacks, especially among people who already have cardiovascular problems, such as diabetes and high blood pressure, or people with a history of heart ailments in families, he says.