Vol. 38, No. 18

3-4-2009
By: Jeff Grabmeier

Distinguished Lecture explores seasonal rhythms

Winter is a harsh season for many mammals, including humans. Both mice and humans are more likely to get sick in the winter and are more likely to die.

Researchers at Ohio State and elsewhere are learning more about how mammals respond to the challenges of winter and the implications these changes have for our health, according to Randy Nelson, Distinguished Professor of Social and Behavioral Sciences.

Nelson discussed cutting-edge research in the field in his University Distinguished Lecture Feb. 19 at the Saxbe Auditorium in the Moritz College of Law.

On many levels, people have long linked winter with sickness, Nelson told the audience. It even shows in our language. In English, cold means both low temperature — such as would be found in winter — and the symptoms of an upper respiratory infection. The same is true of many other languages, he said.

“There’s a linguistic link between seasons and disease,” said Nelson, a professor of psychology and neuroscience.

Nelson and his colleagues have explored, in several studies, just how winter affects the health of mammals.

Hamsters and other non-tropical animals take a cue from the decreasing length of days as winter approaches as a signal to boost their immune system in preparation for the challenges of winter, such as low temperatures and a reduced food supply.

Some mammals essentially shut down their reproductive system during the winter to provide the energy to enhance their immune system and help them survive the winter.

“Adaptations have evolved to allow animals to cope with winter,” Nelson said.

But many mammals have to do even more to conserve energy in the winter. Nelson’s research group has found that hamsters suffer less severe symptoms to infections during the winter. That’s because some of the body’s defenses against infection, such as fever, use a lot of energy during a season when more energy is needed to stay alive.

But it is not just hamsters and mice that respond to the changes of the seasons. Nelson noted that many studies have shown that humans experience seasonal changes in disease and death. Infectious diseases, mental illness and autoimmune diseases such as multiple sclerosis all have strong seasonal components in which symptoms are worse in the winter, he said.

Deaths from cardiovascular disease also peak in the winter, Nelson said. Research at Ohio State in hamsters suggests that the length of daylight may play a key role in this seasonal pattern. In Siberian hamsters, the short days of winter increase inflammation in the body that is linked to cardiac arrest. Inflammation plays a key role in the damage done to the heart and brain by a heart attack.

So how do mammals tell the short days of winter from the long days of summer? Nelson said it all has to do with the hormone melatonin. Light from the eye goes to the brain and regulates the production of melatonin. Melatonin is made in the dark, so more of it is created when the days grow shorter.

Studies have shown that melatonin has key health implications, including enhancing immune function and sickness responses, Nelson said.

And that may be bad news for all of us in the modern world, Nelson said. In addition to the seasonal changes in the amount of light, there is, of course, the daily change from day to night. The invention of artificial light more than 100 years ago has changed how much time humans spend in daylight-like conditions, Nelson said.

“Although light brought great economic prosperity and changed human lifestyles, the results of several experiments show that excessive exposure to light at night reduces the secretion of the pineal hormone melatonin,” he said.

The implications are ominous. Research suggests that areas with high light intensity at night have elevated cancer rates. Nelson’s research group has just begun new studies of the issue, and preliminary results suggest that high exposure to light at night may have other negative effects on health.

“Light at night significantly impairs immune function,” he said.

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