Our Bodies May Only Recognize Two Seasons, Study Finds

Researchers from the Stanford School of Medicine discovered that the human body actually recognizes two seasons, not four. While recent studies found that cellular composition of blood changed according to the time of year, the scientists wanted to identify seasonal biological patterns based on blood molecules, instead of calendar dates.

The study examined what's known as a deep longitudinal multimicrobial profile of the patient’s blood over four years. The molecules in the patient’s blood clustered into two main seasonal patterns, which coincided with peaks in late spring and late fall. 

“We know that several aspects of our environment—light levels, temperature, humidity, pressure, and pollen levels—affect our health,” Tejaswini Mishra, PhD, one of the study's authors and research scientist at Stanford University School of Medicine in California, tells Verywell. “Although there is some data showing the effect of environmental changes on gene activity, for the most part, we do not know how our biological processes and physiology respond to seasonal changes."

This study hopes to add to that knowledge by focusing on seasonal changes in a slew of factors like:

• Gene activity
• Levels of proteins
• Metabolites
• Standard clinical markers

The study clarifies that molecular data could vary according to the country and atmospheric or environmental variations. Other recent studies support this—research in Gambia found the numbers of all seasonal cell types peaked during the June through October rainy season, during which time the immune system faces different pathogenic challenges, such as an increased infectious disease burden, including malaria.

“Understanding the seasonal variation of underlying biological pathways may help us target treatments that can help with seasonal exacerbations of health conditions," study author Sophia Miryam Schussler-Fiorenza Rose, MD, PhD, a professor of genetics at Stanford University, tells Verywell, “Also, given that we found that people with pathological conditions such as insulin resistance exhibit a different seasonality pattern, this suggests that the targets may be different depending on people’s individual conditions.”

How Do Our Bodies React to Spring and Winter?

"The environment is a key factor in human health, and seasonal changes in particular have been associated with human conditions and diseases," the authors wrote.

A total of 105 generally healthy people were in the Standford study. Half of the participants were insulin resistant, or insulin sensitive. Blood samples were taken from these participants four times a year. The scientists then analyzed their metabolism and immunities, as well as their eating habits and exercise routines.

The team found by the end of spring, inflammation skyrocketed. This increase was related to allergies, rheumatic diseases, and osteoarthritis. The first seasonal pattern peaked in late April, while the second seasonal pattern peaked in December and dropped off in March through July.

The scientists also found disorders related to blood pressure, hypertension, and cardiovascular disease to be associated with spring. The study noted the disorders associated with spring are schizophrenia spectrum disorder, sleep pattern, and seizure.

In the winter, the researchers found immune molecules to fight viral infections present in the body, and the rate of acne rose. Blood pressure levels were also generally high.

Understanding Seasonal Changes Can Help

“Everyone should benefit from [these findings]. You can be on the lookout for markers (i.e., blood sugar levels in diabetes) known to reflect health and if they drop unusually low during that period, you might intervene," Michael Snyder MD, an author of the study and professor of genetics at Stanford University, tells Verywell. "Alternatively, if they drop a normal seasonal amount, you might not panic.”

Snyder says you can work to improve on areas of your health known to suffer during certain seasons. “For example, cardiovascular and metabolic makers drop during winter so you can make extra effort to exercise and eat better,” Snyder says. “We can incorporate this information into personal health profiles so that we can better manage people’s health."

According to Mishra, understanding seasonal differences within health can help doctors determine seasonal risk for specific diseases.

“We can use these seasonal analyses to gain more insight into disease processes and their interaction with environmental factors, but you could also imagine finding biomarkers that indicate increased seasonal risk for certain diseases,” Mishra says.

This study was conducted on participants in California, so the study authors stress the importance of environmental factors in understanding findings like these.

“Since this is highly individual and personalized and specific to the geographic location or climate, this type of study would be done locally to capture seasonal human physiology at any geographic location," Mishra says.