A study carried out by Cambridge University as found that just under 25% of our genes are expressed differently between different seasons. They took blood and fat samples from 16,000 people living at different latitudes throughout both the northern and southern hemispheres. What they found was that 5,136 out of 22,822 genes have a different seasonal activity.
They made some key discoveries helping to explain why diseases such as lupus, type 1 diabetes, vasculitis and other autoimmune diseases are more prevalent in winter months. Genes involved in immunity and inflammation are more active in the winter. This usually helps us fight of seasonal bugs which are going around, but sometimes it can lead to negative side effects: autoimmune disease and unnecessary inflammation. Other diseases such as heart disease and mental illness are also aggravated in the winter due to this extra inflammation.
Other benefits having made this discovery include knowing the best time to vaccinate. Vaccinations are more likely to be successful in the winter due to higher activity in the genes responsible for this in the winter months. This suggests we should be trying to give more vaccinations in this season, to improve their efficacy.
The explanation for why this genetic change occurs is unknown but it is thought to be down to different temperatures, effects of different infectious diseases going around and different lengths of days. This discovery could play a big role in how a lot of these diseases are studies because they would need to be looked at without the seasonal interference.