According to today’s report by the European Centre for Disease Prevention and Control there have been 136,432 worldwide reported cases of influenza A (H1N1) resulting in 765 deaths. To put things in perspective only 1 in 178 people, or 0.56% who contract swine flu globally have died from it. Whilst any death is unfortunate, in a given year there are normally 4,000 deaths in the UK and 36,000 deaths in the US attributed to influenza, so there isn’t any extra need to panic.

But if you are obese or overweight there may be some added incentive to lose some weight. During the current swine flu pandemic there have been some observational reports that obesity is a risk factor for complications of the H1N1 virus infection.

There appears to be a correlation between obesity rates in a given country and the percentage of people who die from the swine flu.

There haven’t been official studies into the number of flu victims who are obese, so it’s unknown whether the deaths from swine flu are primarily in obese patients. However, the Morbidity and Mortality Weekly reported the case of ten swine flu patients at a Michigan hospital who became so ill they were put on ventilators. Three of the patients ultimately died from the infection.  Nine of the ten were obese, and two of the three who died were severely obese with no underlying respiratory conditions.

Whilst obesity has not been identified before as a risk factor for flu in humans, researchers at the University of North Carolina have studied the death rate of obese mice when they are infected with the flu virus. For 22 weeks, 70 female mice were fed a normal diet and 70 a high fat/high sucrose diet with all animals then infected with the influenza virus.

Lean mice developed mild disease and only 4% died whereas obese mice got extremely sick and 40% died due to severely impaired immunity. Obese mice also produced lower amounts of anti-inflammatory agents and also took 6 days to produce them, twice as long as the lean mice. Although the study was in mice the researchers think that obesity inhibits the ability of the immune system to respond to influenza infection and suggest that obesity may lead to morbidity from viral infections.

It’s not known whether the mice results are reflected in humans and the excess fat itself makes obese people more vulnerable by inhibiting their immune response. Alternatively it could be that people with a high body mass index who become infected get sicker because of related conditions like heart disease and respiratory complications which are harder to treat and become fatal.

Whilst the science behind the observations has yet to be confirmed, it appears that obese people have yet another health incentive to lose weight.