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FRIDAY, Aug. 27 (HealthDayNews) -- Internal biological clocks may be of benefit only in environments with regular day/night cycles, losing their effect under conditions of constant illumination, according to a Vanderbilt University study.

Researchers reached that conclusion after conducting experiments with blue-green algae, the simplest organisms known to have biological clocks.

The finding offers new insight into internal clocks, which influence a wide range of biochemical functions in humans and other organisms, including sleep and emotional states. The study appears in the Aug. 24 issue of Current Biology.

In the algae, the circadian clock may help switch the organism's photosynthesis system on and off. However, "under constant [illumination] conditions, the circadian clock system is of no benefit and, in fact, might even be bad for the algae," study director Carl H. Johnson, a professor of biological sciences, said in a prepared statement.

Under constant illumination, algae with normally functioning clocks grew at a slower pace than those with clocks artificially disrupted by the researchers. Johnson theorized that, in the absence of a day/night cycle, "the biological clocks may keep shutting down photosynthesis in expectation of the darkness that never comes."

"Circadian clocks are so widespread that we think they must enhance the fitness of organisms by improving their ability to adapt to environmental influences, specifically daily changes in light, temperature and humidity," he said.

"Some people have even suggested that, once invented, these clocks are such a powerful organizational tool that their benefits go beyond responding to external cycles. However, there have been practically no rigorous tests of either proposition."

More information

The University of Pennsylvania has more about the circadian clock.

(SOURCE: Vanderbilt University, news release, Aug. 23, 2004)

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