Scientists have long been intrigued as to why health conditions like rheumatoid arthritis are worse in the winter and improve in the summer. Some arthritis sufferers blame their flare-ups on seasonal temperature changes, but the ebb and flow of some health conditions may have more to do with seasonal changes in immune function than the temperature outdoors. According to a study by an international team of researchers, the immune system you depend each day on to protect you against “bad guys” like pathogenic viruses, bacteria, and even cancer has a seasonal component.

The Seasonal Nature of Immune Function

Researchers at the University of Cambridge analyzed tissue samples from more than 16,000 people living in widely different areas of the world, including Northern and Southern hemispheres. They looked at different types of white blood cells involved in immune function within each tissue and measured the degree of gene expression in each. The researchers were surprised to find the extent of gene expression in these cells varied depending upon the season and time of year the sample was taken. In all, they found about 25% of genes involved in immune function expressed themselves differently based on the time of year. Even when they controlled for factors like geographic location and ethnicity, they still found seasonal expression of genes in cells involved in immune function.

What does this mean? According to the researchers, genes involved in immune function are turned up or turned down based on factors like how many hours of sunlight there are or seasonal temperature changes. In fact, any hormones produced by the human body are regulated by circadian rhythms that follow a 24-hour cycle and are turned on and off by light exposure and other cues from the environment. Cells involved in immune function, too, may be impacted by the changes in day length, temperature or light exposure.

What Are the Implications of This Study?

As the researchers point out, this finding opens up a number of questions. For example, are vaccinations more effective if you get them during the summer and do medications that modulate the immune response perform better at certain times of the year?  People who have autoimmune diseases where their immune system attacks their own tissues often notice their symptoms have a seasonal component with symptoms worsening in the winter. During the winter months, based on the results of this study, genes that suppress inflammation are stifled, allowing inflammation to rage out of control. The increased inflammation, mediated by immune cells, leads to further tissue damage and worsens the unpleasant symptoms people with autoimmune conditions, like rheumatoid arthritis and multiple sclerosis, deal with.

Scientists have long been intrigued by the fact that health problems also occur more frequently in the winter, including heart attacks. Most people blame it on shoveling snow, but inflammation also plays a role in heart disease and heart attacks, raising the question as to whether immune changes during the winter months bears some of the blame. All in all, people tend to feel better and report better health in the summer and seasonal immune system changes may play a role.

The Bottom Line

As the seasons change, so does your immune system. You might not be ready to move to Florida or another area with a mostly sunny climate to keep your immune system healthy, but you can support immune health in other ways by eating a nutrient-rich diet, getting enough sleep, enjoying moderate amounts of exercise, controlling stress and taking immune support supplements. Take care of your immune system – it works hard for you!

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-By Alternative Health Concepts


University of Cambridge. “Seasonal immunity: Activity of Thousands of Genes Differs from Winter to Summer”