Cold weather puts stress on the body, which can lead to various metabolic changes, including suppression of immune function. Even a brief exposure to cold results in increased levels of stress hormones and a number of changes in the immune response. However, by either choice or necessity, many people find themselves not only exposed to winter cold, but having to exercise or do physical labor in cold temperatures, escalating the stress on their bodies. Researchers at the University of Houston reviewed the available literature to examine the effects on the immune system of cold stress combined with physical exertion. In their review, they found that cold and exertion can increase the secretion of stress hormones, compound immune suppression, and may potentially put people at increased risk for colds, flus, and other infections.
The human body adapts to cold weather by stimulation of:
1) the sympathetic (fight or flight stress response) aspect of the nervous system
2) the organs involved in the stress response
- portions of the brain known as the hypothalamus and pituitary, which regulate the stress response
- the adrenal glands, which secrete hormones such as norepinephrine and cortisol that influence stress responses throughout the body
This stimulation causes a number of physiological adjustments to maintain body temperature: shivering to create heat, constriction of small blood vessels near the body’s surface to prevent heat loss, and increased metabolism to generate heat. This same stimulation also causes changes in the immune system. In general, these physiologic adaptations and immune alterations increase as the temperature decreases or the amount of exertion increases.
Such alterations to the immune system result in a decrease in the activity of natural killer cells, which are crucial to preventing the replication of viral-infected and cancerous cells. Natural killer cells are also responsible for the release of chemicals called cytokines that orchestrate additional immune responses. Cold temperatures and the stress response also cause a decrease in the ability of specific immune cells, called T-cells, to reproduce in response to a foreign invader. Cold and stress can also reduce levels of immune factors in saliva (salivary IgA) that play an essential role in immunological defense of the nose, mouth, and upper respiratory system.
The researchers did find that, over time, the body can learn to adapt to some degree of physical exertion in cold weather. Athletes who regularly worked out in the cold secreted less cortisol and had fewer immune alterations than athletes who were not acclimated to the temperature.
If you live in a place where the winters are cold, and especially if you are required to perform physical labor or exercise outside, acclimatize slowly by gradually increasing your exposure to the cold and the intensity of your exertion, and be sure to provide extra support to your immune and adrenal systems during the cold winter months.
About the Author
Dr. Lise Naugle is an associate of Dr. James L. Wilson. She assists healthcare professionals with clinical assessment and treatment protocols related to adrenal dysfunction and stress, and questions regarding the use of Doctor Wilson’s Original Formulations supplements. With eleven years in private practice and a focus on stress, adrenals, hormonal balance and mind-body connection, she offers both clinical astuteness and a wealth of practical knowledge. Dr. Naugle also maintains updated information about the latest scientific research on the hypothalamic-pituitary-adrenal axis function, endocrine balance and nutritional support for stress and develops educational materials about stress and health for clinicians and their patients.
Image Credit: Walking dog in snow by Susan Ujka Larson Collection; man shoveling snow by Flickr user chrispknight
LaVoy EC, McFarlin BK, Simpson RJ. Immune responses to exercising in a cold environment. Wilderness Environ Med. 2011 Dec;22(4):343-51. Epub 2011 Oc 7.