Diseases and Seasonality in TCM: Seasonality of the Immune System

 According to a study by the University of Cambridge, our immune system varies with the seasons, which may help explain why certain diseases (such as heart disease and rheumatoid arthritis) worsen in winter, while people tend to be healthier in summer.

 The results, published in the journal Nature Communications, indicate that nearly a quarter of our genes (5,136 out of 22,822 tested) vary in activity depending on the time of year; some genes are more active in winter, while others are more active in summer. This seasonality also affects our immune cells as well as the composition of our blood and fat tissues.

 Scientists have long known that a variety of diseases, including cardiovascular disease, autoimmune diseases (such as type 1 diabetes and multiple sclerosis), and mental illnesses, exhibit seasonal variations, similar to vitamin D metabolism. However, this is the first study to suggest that this may be due to seasonal changes in our immune system function.

 Professor John Todd, Director of the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory at the University of Cambridge, said: "This is a truly surprising and coincidental finding, as it relates to how we identify and describe the impact of type 1 diabetes susceptibility genes. To some extent, it clearly helps explain why so many diseases—from heart disease to mental illness—are worse in winter. The implications of these results could be profound for how we treat diseases like type 1 diabetes, and even how we plan our research."

 An international team led by the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory at the Department of Medical Genetics, University of Cambridge Medical Institute, analyzed samples from over 16,000 people living in both the Northern and Southern Hemispheres, including the UK, USA, Iceland, Australia, and Gambia. These samples included a mixture of blood samples and fat tissue.

 The researchers used various techniques to study the samples, including analyzing the types of cells found in the blood and measuring the expression levels of individual genes—when a gene is active in a specific cell or tissue, it is considered "expressed," usually involving protein production. They found that thousands of genes were expressed differently in blood and fat tissues depending on when the samples were collected during the year. Similarly, they identified seasonal differences in the types of cells found in the blood.

 The seasonal differences existed in populations mixed from geographically and racially diverse locations—but seasonal genes showed opposite patterns in the Southern and Northern Hemispheres. However, the pattern of seasonal activity was not strongly reflected in Icelandic subjects. Researchers speculated this might be due to nearly 24 hours of daylight in summer and nearly 24 hours of darkness in winter.

 One gene of particular interest is ARNTL, which is more active in summer and inactive in winter. Previous studies have shown that, at least in mice, this gene can inhibit inflammation—the body's response to infection; if the gene has the same function in humans, inflammation levels would be higher during the winter in the Northern Hemisphere. Inflammatory response is a risk factor for a series of diseases, so those at greatest risk may reach a "threshold" in winter where the disease quickly becomes a problem. Drugs targeting inflammatory mechanisms could provide a way to help treat these diseases more effectively during the winter.

 A particularly surprising finding was that a group of genes associated with individual vaccine responses were more active in winter, suggesting that some vaccination programs might be more effective if implemented in winter, as the immune system is already "primed" to respond.

 They believe that during the winter in Europe and Australia, the threshold required to trigger an immune response may be lower, as a direct consequence of our co-evolution with infectious organisms (which are often more common in winter). Interestingly, Gambians showed significant seasonal changes in the number of immune cells in the blood, correlated with the rainy season (June to October), during which infectious diseases, particularly mosquito-borne diseases (such as malaria), are more prevalent.

 Dr. Chris Wallace said: "We know that humans adapt to changing environments. Our study shows that the seasonal differences in the human immune system in equatorial regions (where seasonal changes are not obvious) differ from those in high and low latitude regions, where people have more distinct differences between summer and winter."

 It is not yet clear what mechanism maintains the seasonal changes in our immune system we see; it may be due to environmental factors such as sunlight and ambient temperature. The biological clock inside our body—known as circadian rhythm—is partly coordinated by changes in sunlight, which also explains why people who do not follow daily cycles, such as factory shift workers or long-haul flight staff, may have poorer health.

 Professor Todd added: "Given that our immune system seems to place us at greater risk of inflammation-related diseases in colder seasons with shorter daylight hours, and given the benefits we already know from vitamin D, we can understand why people want to get some 'sun' in winter to improve their health."

 Professor Mike Turner, Director of Infection and Immunobiology at the Wellcome Trust, said: "This is a good study providing empirical support for the common view that we tend to be healthier in summer. In this sense, seasonality is an interesting finding: the activity of many of our genes, and the composition of our blood and fat tissues, varies according to the season. Although we are not yet clear about the mechanism behind this change, one possible outcome is that treatments for certain diseases, if customized according to the season, may be more effective."

 Karen Addington, CEO of JDRF UK, said: "We have long known that more people are diagnosed with type 1 diabetes in winter. This study reveals the reason. It identifies a biological mechanism we previously did not know that makes the body more prone to the autoimmune attack seen in type 1 diabetes on a seasonal basis."

 "We all like the winter sun, and flying south for the winter is not a preventive measure for type 1 diabetes that anyone can take. But this new insight opens up new research avenues that can help us unravel the complex network of genetic and environmental factors behind the diagnosis."

 San Fu Feng Yun Yong Zhu: In Traditional Chinese Medicine (TCM), part of Chinese traditional culture, seasons have always been correlated with diseases since ancient times. In the past, due to insufficient sample sizes, this statistical feature existed but was not very obvious. In the Five Elements theory of TCM, as mentioned above, heart disease belongs to Fire, while winter belongs to Water. Fire is controlled by Water in the water season, which is also the reason why heart disease worsens. Similarly, mental illness itself belongs to the symptoms of Teng She (a mythical snake), which is Si Fire syndrome, so it also worsens in winter. The greatest significance of this discovery lies in preliminarily determining that these are related to the immune system, which indicates that many treatment plans in TCM are aimed at regulating the immune system—this points out a problem in the so-called integration of Chinese and Western medicine today: many so-called integrations involve Westernizing Chinese medicine, attempting to understand it from the perspective of drug sterilization and antiviral action, which is clearly an incomplete understanding. This is also why modern TCM research has struggled to progress.