It was found that younger men had a trend towards higher mortality despite lower consumption. But this became significant at about 28 cups per week where there was a 56 percent increase in mortality from all causes.

Younger women who consumed more than 28 cups of coffee per week had double the risk of dying from all causes than those who did not drink coffee, the study said.

"For those drinking high amounts, there should be some caution, as this dose was associated with at least a signal for increased total mortality in this large study, especially in those under 55 years of age," Xuemei Sui, the study's co-author from the University of South Carolina in Columbia.

"My review is that it is safe to drink low doses (1 to 2 cups and probably 2 to 3 cups per day) of coffee, with even some potential benefits of the low dose," Sui said but adding: "Moderation is the key. Avoid excess drinking coffee."

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