For most of us, cold winters call for warm jackets, nights by the fire– and plenty of tissues. People spend more time indoors where viruses can spread more easily. The chill itself doesn't help. In fact, cold dry air inhibits your immune system's protective capabilities. Besides the threat from microbes and frosty weather, does our immunity itself fluctuate throughout the year?
Research suggests your immune system may be more prone to change through the seasons than you might think. Statistically, conditions like cardiovascular disease, psychiatric disorders, and autoimmune conditions flair up in the winter. It might also explain why people usually enjoy better health during the summer. Here’s a closer look at how your immune system changes with the seasons.
The Link to Your Genes
The reason seasonality affects your immune system is that the activity of your genes fluctuates with the time of year. Genes control every body process, from how tall you grow to the color of your hair, by means of DNA coding. They also control how well your body can adapt to stressors, or your immunity.
One study led by the University of Cambridge analyzed over 23,000 genes and their impact on overall immunity. The researchers discovered that about 23 percent of these genes have different activity depending on the time of year. Some increased in activity in the summer, but others increased in activity over the winter. Some of these genes include those that control white blood cells (a major aspect of the immune system) and the contents of adipose tissue (which stores fat).
Interestingly, the research also found that blood composition changes with season, which could be due to changes in gene expression. Differences in blood composition mean that the types of cells present in the blood change with the season.
Comparing the Northern and Southern Hemispheres
To keep a broad, diverse subject population, the researchers compared gene expression from people in the northern hemisphere (the UK and Ireland, the U.S., and Iceland) with a similar group from the southern hemisphere (using Australia) and a population from Gambia, an equatorial country. It turns out that genes of seasonal activity reacted similarly in almost all subject populations, regardless of geographical location. Genes that were expressed to a greater extent during the summer in people in the northern hemisphere also had higher expression during December, January, and February in people in the southern hemisphere. The exception was in Iceland, where there was less of a clear distinction between seasons. The researchers postulated that this was likely due to days of almost full darkness during the winter and of almost total sunlight during the summer.
People in Gambia, despite being on the equator, also showed seasonal differences in their gene expression, having more activity in their immune cells during the rainy season when there is a higher risk of contracting diseases carried by mosquitoes, like malaria.
What Influences Seasonal Variation?
Something the study was unable to determine with certainty is how seasonality is apparent to the cells of your immune system. Our bodies may take cues from the environment, such as average daily temperatures and hours of sunlight.
This is even more likely considering that circadian rhythms (your internal body clock) rely on daylight to function properly. It also may explain why people who have an irregular schedule are at higher risk of health problems. Interestingly, despite a near-constant climate in equatorial regions, people’s circadian rhythms can still detect changes in season. Rather than being due to day lengths (which remain the same all day), internal body clocks detect smaller climatic changes, like rainfall, and food availability.
ARNTL, a key gene that is more active in the summer, is known to prevent inflammation in mice. If the gene does the same in humans, lower expression in winter could imply that inflammation may be more likely during the colder months of the year. This is important because inflammation is a major risk factor for several diseases.
There’s also some good news: genes related to vaccination response increase in activity in the winter. This means you may be able to expect greater immunity from infectious diseases if you receive immunization at this time of year.
What Diseases Have Seasonality?
Knowledge of fluctuating severity in diseases throughout the year has been known long before this research. Some of the many illnesses and conditions in this list include:
- Type 1 diabetes
- Multiple sclerosis
- Heart disease
- Mental illness
- Rheumatoid arthritis
- Childhood infectious diseases, including varicella, pertussis (whooping cough), and meningitis
Due to a higher volume of receptors in the summer, seasonal change also has a significant impact on vitamin D production in the body.
The study concerning fluctuations in seasonal immunity and the conclusions drawn could have profound implications for how medical professionals treat diseases depending on the time of year. In addition, it’s useful information for people managing their own health conditions and anyone looking to optimize immunity year round.
So, what can you do to take care of your immunity during the changing seasons? Essential oils can be an effective option to keep your immune system healthy and functional, regardless of the season or time of year. You can find a range of immune boosting essential oils, such as the Immunity & Respiratory Combo, at LaCura. Check out our online store to find the right product for you.