Scientists have found evidence linking seasonal changes to variances in immune system gene expression. [arquiplay77/iStock]
Scientists have found evidence linking seasonal changes to variances in immune system gene expression. [arquiplay77/iStock]

Often when we think of health in relation to the seasons we conjure up images of runny noses, nasty coughs, and rampant flu for the wintery months and conversely, vigor, radiance, and well-being for the warmer days. Now, researchers from the Juvenile Diabetes Research Foundation /Wellcome Trust Diabetes and Inflammation Laboratory in the U.K. have evidence to explain why certain conditions, such as heart diseases, type 1 diabetes, and rheumatoid arthritis are worsened during the winter and why, in general, individuals tend to be healthier in the summer.         

While scientists have had evidence for some time that numerous diseases displayed variation that seemingly matched seasonal changes, the current study is one of the first instances to provide evidence that this may be the result of immune system variances due to seasonal change.

“This is a really surprising—and serendipitous—discovery as it relates to how we identify and characterize the effects of the susceptibility genes for type 1 diabetes,” explained John Todd, Ph.D., director of the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory and senior author on the study. “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.”

The findings from this study were published today in Nature Communications through an article entitled “Widespread seasonal gene expression reveals annual differences in human immunity and physiology.”

The researchers examined over 16,000 samples of blood and adipose tissue from individuals residing in both the northern and southern hemispheres, including the U.K., U.S., Iceland, Australia, and The Gambia.

Using an array of techniques, the scientists looked at various cell types in the blood, as well as the expression levels for various genes. What they found was that thousands of genes were differentially expressed depending on what time of the year the samples were taken. Furthermore, seasonal differences were observed across mixed populations and ethnically diverse backgrounds, the patterns of seasonal activity however, were opposing in samples from the northern and southern hemispheres.   

“We know that humans adapt to changing environments,” stated Chris Wallace, Ph.D., research fellow at the Wellcome Trust and co-author on the current study. “Our paper suggests that human immune systems adapt to show different seasonal variation in equatorial regions with fewer distinct seasons compared to regions at higher and lower latitudes with more pronounced differences between winter and season.”

Interestingly, the investigators found a gene, ARNTL, which codes for a transcription factor that suppress inflammation in mice that was much more active in the summer and less in the winter. If this gene has the same function in humans, this could help explain why certain disorders with close associations to inflammatory mechanisms would cause individuals to reach the threshold at which the disease becomes a problem much sooner in winter time.

“Given that our immune systems appear to put us at greater risk of disease related to excessive inflammation in colder, darker months, and given the benefits we already understand from vitamin D, it is perhaps understandable that people want to head off for some winter sun to improve their health and well-being,” concluded Dr. Todd.

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