In some ways, it’s obvious – it helps explain why so many diseases are much worse in the winter months – but no one had appreciated the extent to which this actually occurred
John Todd
The study, published today in the journal Nature Communications, shows that the activity of almost a quarter of our genes (5,136 out of 22,822 genes tested) differs according to the time of year, with some more active in winter and others more active in summer. This seasonality also affects our immune cells and the composition of our blood and adipose tissue (fat).
Scientists have known for some time that various diseases, including cardiovascular disease, autoimmune diseases such as type 1 diabetes and multiple sclerosis, and psychiatric disorders, display seasonal variation, as does vitamin D metabolism. However, this is the first time that researchers have shown that this may be down to seasonal changes in how our immune systems function.
“This is a really surprising – and serendipitous – discovery as it relates to how we identify and characterise the effects of the susceptibility genes for type 1 diabetes,” says Professor John Todd, Director of the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory. “In some ways, it’s obvious – it helps explain why so many diseases, from heart disease to mental illness, are much worse in the winter months – but no one had appreciated the extent to which this actually occurred. The implications for how we treat disease like type 1 diabetes, and even how we plan our research studies, could be profound.”
An international team, led by researchers from the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory in the Department of Medical Genetics, Cambridge Institute for Medical Research, examined samples from over 16,000 people living in both the northern and southern hemispheres, in countries including the UK, USA, Iceland, Australia and The Gambia. These samples included a mixture of blood samples and adipose tissue.
The researchers used a variety of techniques to study the samples, including looking at the cell types found in the blood and measuring the level of expression of the individuals’ genes – a gene is said to be ‘expressed’ when it is active in a particular cell or tissue, usually involving the generation of proteins. They found that the thousands of genes were expressed differently in blood and adipose tissue depending on what time of year the samples were taken. Similarly, they identified seasonal differences in the types of cells found in the blood.
Seasonal differences were present across mixed populations in geographically and ethnically diverse locations – but the seasonal genes displayed opposing patterns in the northern and southern hemispheres. However, the pattern of seasonal activity was not reflected as strongly in Icelandic donors. The researchers speculate that this may be due to the near-24 hour daylight during summer and near-24 hour darkness in winter.
Image: Changing of the seasons
Credit: Luke Price
Reproduced courtesy of the University of Cambridge