Why is there a decline in immunity depending on the seasons?
Many of us experience a decline in fitness and increased vulnerability to infection during seasonal changes, particularly in the fall and winter.
💡 But why does our immunity fluctuate so much? The answer lies in several physiological, environmental, and behavioral factors. Here's an in-depth analysis, backed by scientific research.
The impact of climate on the immune system
Cold temperatures and their effect on the body
Studies show that exposure to cold reduces the effectiveness of the immune system by slowing down certain immune responses.
For example, low temperatures decrease the response of the respiratory mucous membranes , which are our first line of defense against infections. (1)
Humidity and virus transmission
In winter, the air is drier, which favors the transmission of viruses.
Low humidity allows viral particles to remain suspended longer
long time, thus increasing the risk of infection. (2)
Reduced sun exposure and decreased vitamin D
Vitamin D plays a fundamental role in the regulation of immune defenses.
However, in autumn and winter, sun exposure decreases sharply, leading to a drop in vitamin D levels in the body and, consequently, a decrease in the effectiveness of the immune system. (3)
Research shows that insufficient vitamin D levels are associated with increased susceptibility to respiratory infections, including the flu and the common cold. (4)
Lifestyle changes and their consequences
The seasonal decline in immunity is multifactorial : climate, declining vitamin D levels, lifestyle changes, and increased indoor contact all play a significant role.
To limit this decline, it is essential to adopt good habits : vitamin D supplementation, a diet rich in micronutrients, regular physical activity and maintaining a healthy lifestyle.
By incorporating these strategies, it is possible to naturally strengthen our immunity and better resist seasonal infections.
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References:
(1) Eccles, R. (2002). "An explanation for the seasonality of acute upper respiratory tract viral infections". Acta oto laryngologica, 122(2), 183-191.
(2) Lowen, AC, Mubareka, S., Steel, J., & Palese, P. (2007). "Influenza virus transmission is dependent on relative humidity and temperature". PLoS Pathogens, 3(10), e151.
(3) Aranow, C. (2011). "Vitamin D and the immune system". Journal of Investigative Medicine, 59(6), 881-886.
(4) Ginde, AA, Mansbach, JM, & Camargo, CA (2009). "Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey". Archives of Internal Medicine, 169(4), 384-390.
