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U.S. researchers have come up with a new way for travellers to recover quickly from jet lag - don't eat for 16 hours.

They made the discovery while investigating the internal biological clock that governs our daily sleep-wake cycle.

Scientists have long known that our 24-hour "circadian rhythm" is regulated by a group of cells in the hypothalamus region of the brain. These cells, which represent the body's main clock, are sensitive to changes in light conditions registered through the optic nerve in the eye.

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Researchers at Harvard Medical School and Beth Israel Deaconess Medical Center in Boston have now pinpointed a second clock that is set by the availability of food. Their study, published today in the journal Science, is based on research on mice. But they believe all mammals, including humans, possess an internal food clock, too.

Clifford Saper, the senior author of the study, said this second clock probably takes over when food is scarce. It may have evolved to make sure mammals don't go to sleep when they should be foraging for food to stay alive.

Dr. Saper says long-distance travellers can probably use this food clock to adjust rapidly to a new time zone.

"A period of fasting with no food at all for about 16 hours is enough to engage this new clock," he said in a statement released with the study. Once you eat again, your internal clock will be reset as though it is the start of a new day.

Although more research is needed to confirm the findings, travellers could probably activate the second clock in the following way: On an overnight trip to Europe, fast before the flight and don't eat on the plane. After you arrive the next morning, eat a nutritious meal.

Normally, the body's light-driven main clock takes a long time to adapt to a foreign location, adjusting by only an hour or two each day.

"The neat thing about this second clock is that it can override the main clock ... and you should just flip into that new time zone in one day," Dr. Saper said in an interview.

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ANTIDEPRESSANTS

IN PREGNANCY

Expectant mothers can safely use antidepressant medications during the first 14 weeks of pregnancy without fear of the drugs causing birth defects, according to a Quebec study.

Researchers at the Université de Montréal and Sainte-Justine Hospital used data from the Quebec Pregnancy Registry to assess possible risks of taking antidepressants during this critical period of fetal development when limbs and major organs start to take shape.

"In terms of birth malformations in this population, we found no difference between women who used antidepressants and those who did not use antidepressants during their first trimester," the senior researcher Anick Bérard said in statement released with the study, published in The British Journal of Psychiatry.

Previous studies have indicated that depressed patients who stopped taking their medications during pregnancy are at an elevated risk of later developing postpartum depression.

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"They are better off continuing with their medications because they will be better able to care for their baby."

DOPE, A HEART RISK?

Smoking marijuana may boost your chances of having a heart attack or stroke, according to a U.S. government study. But you apparently have to do an awful lot of dope.

The researchers found elevated levels of a specific protein called apolipoprotein C-III in the bloodstream of heavy marijuana users.

This protein, in turn, leads to increased levels of triglycerides, fats that can clog arteries and increase the risks of heart disease and strokes, said lead researcher Jean Lud Cadet of the U.S. National Institute on Drug Abuse.The 18 marijuana users who volunteered for the study smoked between 78 and 350 joints a week. The average was 130.

Dr. Cadet acknowledged that's an unusually large amount and said he was surprised by their level of consumption. "They don't have jobs, they don't go to school, they basically spend their time smoking marijuana," he said in an interview.

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Dr. Cadet can't say whether moderate and occasional smokers also have elevated levels of the protein without doing another study.

Marijuana activists said the high levels of pot used in the study, published in the journal Molecular Psychiatry, render the results meaningless.

"If you do anything to that level of excess, it might well have some untoward effects, whether it's marijuana or wine or broccoli," Bruce Mirken of the Marijuana Policy Project, told Reuters.

ptaylor@globeandmail.com

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