Winter blues - why are we healthier in the summer?


As new figures support the argument that we’re healthier in summer time - we take a look at why we suffer from the winter blues. 

The University of Cambridge has completed a study that explains how our immune system changes with the seasons.

Environmental factors

The researchers looked at sample genes from people living in the northern and southern hemispheres. They discovered that activity in nearly a quarter of 23,000 genes tested changed depending on the time of year

A particularly interesting finding was that the gene ARNTL – known to suppress infection in mice - is much more active in the summer. 

The study suggests many of the genetic changes could be down to environmental factors, including changes in the amount of daylight and the ambient temperature. 

Daylight plays a large role in the running of the body’s circadian rhythm, or body clock

This could be why people who work night shifts have been known to suffer with poorer health than those on standard day shifts. 

To add to the evidence that sunlight and circadian rhythms play a large role in the health disparity, the research found that in Iceland - which enjoys near 24-hour daylight in the summer and total darkness in winter - the results were less pronounced.

What is affected?

The study claims those who suffer from mental illness, diabetes, arthritis and heart disease fare worse in the winter months. 

Professor Mike Turner, head of infection and immunobiology at the Wellcome Trust, says the results are fascinating, explaining that the activity of not just our genes but also the composition of our blood and fat tissue, varies depending on the time of year. 

Researcher Chris Wallace says that these results point to a human immune system that can adapt to seasonal variations. 

Professor John Todd, director of the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory says it will have implications for how diseases like type 1 diabetes are treated.

Other factors 

Outside of the genetic changes, there are a number of other factors that could be influencing our health during the seasons. 

  • Vitamin D is known to boost our immune system. Our main source of this is from the sun, so it makes sense that our immune system functions better in the summer.
  • On extremely cold days, your core body temperature can drop (hypothermia) which causes your immune system to slow. This is particularly noticeable in older people.
  • Warming your house can cause colds to spread as minute droplets from a sneeze can survive and prosper in the heated, dry air.
  • Dry and cold winter air, according to The National Institutes of Health, allows the flu virus to survive better. It suggests that the flu virus’s coating becomes harder at lower temperatures, making it easier to transmit.

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