SCIENCE

With Melatonin, Timing Is Key

Melatonin, which millions of people take to try to adjust to time-zone changes or night shifts, helps people sleep only if it is taken at a time when the body's natural levels of the hormone are low, according to new research.

The findings could help explain why previous studies of melatonin have produced mixed results.

Charles A. Czeisler of the Brigham and Women's Hospital in Boston and colleagues studied the sleep patterns and melatonin levels of 36 healthy young adults before and after giving them either melatonin or a placebo to see if the hormone would help them adjust to the equivalent of crossing four time zones.

Melatonin improved the volunteers' ability to sleep only when they took it during the day, when their bodies were not producing melatonin in response to exposure to light, the researchers report in today's issue of the journal Sleep.

"Melatonin enabled these participants to obtain an extra half hour of sleep when they attempted to do so during the day, at a time when they were not producing melatonin themselves," Czeisler said. "Melatonin did not help these young adults sleep at night, when their body was already producing melatonin. These findings have implications for millions of people who attempt to sleep at a time that is out of synch with the brain's internal clock."

-- Rob Stein

Signs of Resilience in Corals

Although most corals face a dire fate if the world's oceans continue to warm, some reefs appear able to survive higher water temperatures by accelerating their feeding rates, according to a study in Friday's issue of the journal Nature.

The study, by scientists at Ohio State, Brown and Villanova universities, found that the Hawaiian branching coral Montipora capitata managed to recover from bleaching associated with global warming by increasing its intake of tiny plankton. However, other species, such as Porites compressa and Porites lobata , did not.

The new findings are significant because climate change represents the greatest single threat to the future survival of coral reefs. Scientists predict that as much as 60 percent of reefs worldwide may die in the next few decades because of warmer ocean temperatures.

Once the water warms, the single-celled algae (called zooxanthellae) that live inside the corals leave, depriving them of their color and most of their food energy. However, some corals such as Montipora capitata can use small tentacles to grab passing plankton and digest them, allowing them to recover from bleaching incidents.

Andrea Grottoli, a geological sciences professor at Ohio State and the paper's lead author, said that, though scientists might be able to encourage corals "to eat a bit more," she suspects species that are more inclined to feed will do better while others will die out.

"There's a glimmer of hope that there's a resilience in corals we didn't appreciate before, but I would be reluctant to say corals are now going to survive," said Grottoli, who wrote the paper along with Brown graduate student James Palardy and Villanova postdoctoral research fellow Lisa Rodrigues. "It's still pretty grim."

-- Juliet Eilperin