Human bodies are regulated by biological clocks called "circadian rhythms." These rhythms are dependant on body temperature, plasma levels of certain hormones and other biological conditions. All these factors ensure we are alert and active on exposure to sunlight and tired and sleepy during the evening.

When traveling on long flights that involve changing time zones, the biological clock maintains its original schedule and hence travelers are likely to feel active during night time and sleepy during day time. It is possible to adjust after some rest, but business travelers who are on tight schedules do not appreciate jet lag. Neither does anybody else for that matter!

This is where the current study, published in this week's Proceedings of the National Academy of Sciences, could be a useful pointer.

Viagra is chemically sildenafil and is best known for treating erectile dysfunction. The drug was initially marketed as a high blood pressure and angina relieving medication, but quickly acquired superstar status because of its ability to treat erectile dysfunction in a satisfactory manner.

Produced by Pfizer, the drug is a blockbuster in this category. While other beneficial effects have been attributed to Viagra, it continues to be the number one drug in the ED category.

In the current study, researchers from the National University of Quilmes in Argentina decided to test the effect of Viagra on jet lag. To this effect they shifted the light-dark cycle in hamsters and subjected them to a east bound flight of six hours.

The light-dark cycle is an important parameter in mammals because it makes them active when it is light and triggers rest/sleep when it is dark. The hamsters in the study were injected measured doses of Viagra and their light-dark cycles adjusted so as to mimic the effect of a six-hour plane trip to the east.

The Viagra-filled hamsters were able to recover 25 to 50 percent more quickly as compared to human jet lag. They needed less time to "reset" their biological clock to the prevailing conditions, according to Dr. Diego Golombek, a researcher with the Universidad Nacional de Quilmes in Buenos Aires.

Golumbek added that Viagra seemed to work by preventing the breakdown of a molecule called cGMP. This molecule is present in higher levels during day time and breaks down during the night. Viagra blocked an enzyme that regulated the breakdown of cGMP.

The limitation of the study was that Viagra seemed to work only when lights were switched on early. Furthermore the drug produced positive results only when eastward travel was simulated. These results were not replicated during westward journeys.

Golombek said it was tough to predict what effect Viagra would have on humans because hamsters have a faster metabolic rate than humans. He added that larger trials involving animals and then humans would be needed, but human trials would be expensive because they would need to test the drug in real flight situations. However he said their study was another possible cure for jet lag because Viagra exerted the same effects as melatonin, which is used to treat jet lag.

Viagra maker Pfizer said the study was interesting. It added that the drug was only approved for treating ED and should be used as such until new indications, if any are approved.

Jet lag is a time tested phenomenon in frequent travelers. It can be a disconcerting effect particularly if traveling long distances. The National Institutes of Health has the following tips to avert jet lag:

    * Maintain a sensible bedtime schedule prior to your trip. Don't avoid sleeping in order to make yourself tired.
    * Consider going to bed earlier for a couple of nights before leaving if you are traveling east. Go to bed later for a couple of nights if you are traveling west.
    * For short trips, maintain a schedule of eating and sleeping at your usual time, if possible, while at your destination. For longer trips, try to adapt to the time schedule to which you're traveling before you leave. Set your watch to the new time as you begin the trip.
    * Drink plenty of liquids, but avoid alcohol and caffeine.
    * If you exercise regularly, continue to do so at your destination. Avoid exercising late in the evening, because it can keep you awake.
    * For important events or meetings at your destination, try to arrive ahead of time to allow for the time difference.
    * Melatonin, a hormone sold in supplement form at health food stores, may help decrease jet lag. Try taking 1 - 3 milligrams of melatonin at several hours before bedtime for several days once you arrive at your destination.