Seasonal shifts

Bodies divide the year in two — at least in parts of California

Photo of a gardenia blooming by Paul Hart

Mother Nature’s traditional signals — think crunchy leaves or wildflower blooms — teach us that there are four seasons. But some bodies see it differently.

Stanford scientists have found that our bodies’ molecular changes ebb and flow in patterns, but not necessarily in the way you’d think. According to their study of people from the San Francisco Bay Area and Southern California, the human body has two seasonal turning points: late spring-early summer and late fall-early winter.

The late-spring period coincided with a rise in molecules that play a role in allergies and arthritis. Come winter, scientists saw an increase in molecules that fight viral infection and in those involved in acne development. Signs of high blood pressure were also higher in the winter.

“Many of these findings open up space to investigate so many other things,” said postdoctoral scholar Reza Sailani, PhD, a lead author of the study, published Oct. 1 in Nature Communications. “Take allergies, for instance,” he said. Pairing readouts of molecular patterns with pollen count data could pinpoint specific allergy triggers.

More broadly, the findings provide insights for better drug trials. Researchers studying a drug for high blood pressure, for example, can factor in that blood pressure spikes in winter — so a Bay Area trial started then, rather than spring, would likely have a different result.

Researchers tracked molecular data from more than 100 people living in the Bay Area and three from Southern California over four years. In that time, more than 1,000 molecules waxed and waned over yearlong time spans, with participants experiencing the two key transitional periods.

“You might say, ‘Well, sure, there are really only two seasons in California anyway: cold and hot.’ That’s true, but even so, our data doesn’t exactly map to the weather transitions either. It’s more complicated than that,” said Michael Snyder, PhD, professor and chair of genetics, and senior author of the study.

One caveat, Snyder said, is it’s likely that the molecular patterns of people in other parts of the country will differ, depending on atmospheric and environmental variations.

Photo by Paul Hart/Adobe Stock Images

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Hanae Armitage

Hanae Armitage is a science writer in the Office of Communications. Email her at

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