The excess of deaths during the winter months is often due to factors other than temperature. A global warming trend won't change that, researchers concluded.

Experts from Columbia University's Mailman School of Public Health analyzed mortality data, spanning 1971 to 2007, in 39 cities in the United States and France to determine just how much cold temperatures factor into winter's excessive mortality rates. Data was pulled from the U.S. National Center for Health Statistics and the French National Institute for Statistics and Economics Studies.

The selected cities varied significantly by demographics, layout and socio-cultural background, according to Patrick L. Kinney, the study's lead author.

The researchers sorted the cities by their winters: cold or mild. They found out that deaths rose comparatively across all of the cities and over decades despite how cold or warm the winters were.

"Some have claimed that warmer winters due to climate change will lead to big reductions in winter deaths," said Kinney. "Our work suggests that this is unlikely to be the case."

The cold weather isn't a primary factor in the deaths of most senior citizens during the winter months, Kinney stated. Most of the deaths can be attributed to flu and other respiratory issues, he said.

The researchers concluded that increased time indoors, low humidity, lack of exercise and other factors, affect the immune system during winter and facilitate the rise in mortality rates.

"Unfortunately the holiday season probably plays a part," said Kinney. "When older people mix with the younger generations of their families, they come into contact with all the bugs that the kids have brought home from school."

Neither a common cold nor winter mortality rates can be blamed totally on cold weather, but it definitely plays an indirect role in winter deaths since frigid temperatures encourage individuals to spend more time indoors and less time exercising.

While Kinney and company sought to prove or debunk the belief that cold weather increases winter deaths, the team kept its work in perspective and spoke of the broader implications of such research.

"We need to know the potential impacts of climate change on health so that we can plan public health interventions, accordingly," said Kinney.