Common seasonal influenza explains much of the difference in mortality rates between winter and summer. (Photo: Colorbox)
Common seasonal influenza explains much of the difference in mortality rates between winter and summer. (Photo: Colorbox)

Winter can be the ultimate chill-out

If you have reached the autumn of your years, watch out for winter! For reasons which are not wholly clear, from age 70 the odds of death in January or February are much higher than in the rest of the year.

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In January 2012, deaths in Norway totalled 3,763. The number was 15 percent higher than in July the same year, when the death toll was 3,270.

Was the difference of 493 deaths just a random blip, a statistical anomaly? Certainly not. Year after year, more people die in the winter months than in the summer months. The same is true for Australia and New Zealand, except the peak “down under” is of course in their winter months June, July and August.

In an article in the Norwegian medical journal, Tidsskrift for Den norske legeforening, statisticians Elinor Ytterstad and Tormod Brenn of the University of Tromsø did the maths on all the deaths in Norway from 1991 to 1995.

They found that a 12 percent higher number of people died in the winter half of the year than in the summer half. When they checked age groups for higher mortality rates in the winter they found the added risk started for women from age 71 and for men from age 68.

Seasonal influenza takes the lives of many elderly during the winter months. The Norwegian Institute of Public Health recommends all elderly to take flu vaccines. (Photo: Colorbox)
Seasonal influenza takes the lives of many elderly during the winter months. The Norwegian Institute of Public Health recommends all elderly to take flu vaccines. (Photo: Colorbox)

Cardiovascular and pulmonary diseases take bigger tolls in the winter. Cancer victims, for instance, do not have a higher risk of dying in these months.

No better in the Mediterranean countries

Oddly, there is no direct link between how frigid the weather is and how many die in the winter.

A higher rate of deaths is registered in winter in all the northern countries, like Norway, but they are not alone.

Mortality rates are even higher in the winter months in Spain and Portugal than in the Nordic countries. The same goes for the UK, Japan, France and Italy, according to Claudia Wells of the Office for National Statistics in Great Britain, when interviewed by the BBC News Magazine.

One explanation is that people in the Mediterranean often dwell in homes with poor insulation and are chillier indoors in winter than those who contend with annual snow and ice and thus keep their homes warmer.

Brenn points out that in Siberia the jump in winter death rates is lower than in the Nordic countries.

Is it all a case of flu?

Scientists think common seasonal influenza explains much of the difference between winter and summer mortality rates. Flu is a winter phenomenon in Europe.

The typical flu months in Norway are December and January.

Ytterstad and Brenn’s figures show an average of 2,589 more deaths in Norway in the winter half of the year than the summer half.

Nobody knows exactly how much of this can be explained by flu epidemics. But a University of Oslo statistician, Jon Michael Gran, has studied the issue.

Gran sees that the higher rate of deaths in the winter months coincide with the peak numbers of flu cases.

Around 900 die of flu

Siri Helene Hauge, a specialist in social medicine at the Norwegian Institute of Public Health, confirms that the exact numbers of annual flu and flu-related deaths in Norway are unknown. 

But the Institute estimates that around 900 people in Norway, elderly for the most, die of influenza in the course of the flu season.

“Influenza can lead to an aggravation of primary diseases, such as cardiovascular disease or chronic obstructive pulmonary disease (COPD). This is why influenza is not registered as the cause of death,” says Hauge.

“That is the reason why we don’t have exact figures for influenza deaths.”

Annual flu shots recommended

The Norwegian Institute of Public Health recommends that everyone in risk groups should go to their MDs and get vaccinated against influenza, particularly those over the age of 65.

“Only round half of the people we recommend flu shots to actually go and get vaccinated,” Hauge informs.

New statistics from the UK show deaths not only peak during winter, but they tend to spike sharply right before and right after Christmas.

The highest numbers of deaths in British hospitals are seen in the first two weeks of January, according to BBC News.

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Read the Norwegian version of this article at forskning.no

Translated by: Glenn Ostling

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