Could being happier help you fight infectious disease? © Getty Images

Could being happier help you fight infectious disease?

Here’s something to smile about: simply being in a better mood could ward off illness.

We’ve all heard the saying ‘laughter is the best medicine’. And there might be something in this idiom: numerous studies have shown that people who report greater happiness tend to have better medical outcomes.

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For instance, a 2017 study at the University of Nottingham tested the effect of mood on 138 pensioners receiving the normal flu jab. Those that felt happy on the day of the vaccination went on to produce more flu-fighting antibodies. Earlier work at Yale University and the University of Florida has also shown that your mood affects the activation of genes that fight disease.

But does happiness cause good health, or is it the other way around? After all, it could be that people who have robust immune systems naturally have higher levels of other mood-improving brain chemicals as well.

There is a possible evolutionary explanation here. Humans evolved as social creatures that cooperate in groups to secure food and protect themselves from wild animals. We were happier with a close network of friends and family because this improved our survival chances.

But closely socialising groups are also breeding grounds for respiratory infections such as flu and colds, so we would have needed to increase the activity of the genes that fight these diseases.

For lonely outcasts, however, infectious disease was less of a problem, and genes that help recover from physical injury may have been prioritised instead.

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