8-hour workday biologically hard-wired

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By Jennifer Harper

Attention, workaholics: Twelve hours on the job may go against Mother Nature.

Don't fight that 5 p.m. whistle. New research from the University of Pennsylvania and the Salk Institute for Biological Studies suggests that humans are biologically hard-wired to work only eight hours a day.

The standard work cycle appears to be programmed in the genes.

"There is the possibility that there could be a biological basis to an eight-hour cycle," said senior author John Hogenesch, an associate professor of pharmacology at the University of Pennsylvania.

His research team focused on the "circadian clock" that coordinates human physiological and behavioral processes on a 24-hour rhythm. People anticipate changes in their environment and prepare accordingly. In the course of a day and night, thousands of genes are affected - switching on and reacting to outside stimulus with predictable regularity.

Previous research has concentrated on the 12-hour cycles governed by light and dark, which set our regular waking and sleeping hours and eating habits. When the timely inner routine gets disrupted, the body can suffer from jet lag - or worse. A compromised clock has also been linked to cardiovascular and metabolic diseases, cancer and aging-related disorders.

By studying the gene activity of mice every hour for 48 hours, Mr. Hogenesch and his team were surprised to find that shorter cycles of the circadian rhythm are also biologically encoded. They found that 260 genes were activated every 12 hours.

"There is an obvious biological basis to a 12-hour rhythm. The 12-hour genes predicted dusk and dawn. These are two really, really stressful transitions that your body goes through and your mind goes through. Anybody who has young children realizes that they are more likely to cry around those times - and you're more likely to cry with them," Mr. Hogenesch said.

But the team also found that another set of 63 genes became active at eight-hour intervals.

It is a small finding with big implications, suggesting there is "a biological basis for the eight-hour workday," the study said.