THE SEASONS OF YOU

THE CALENDAR YEAR FOLLOWS THE PATTERN OF SPRING, SUMMER, AUTUMN, WINTER. BUT PERHAPS IT SHOULDN’T…

- Susan D'Agostino

Ancient Egyptians identified three seasons based on cycles of the Nile River: inundation, emergence and harvest. In tropical countries, it’s the rain that tends to divide the year in two: a wet and a dry season. Elsewhere the calendar demarcates four seasons: autumn, winter, spring and summer.

But now, researchers at Stanford University have found that human biology, rather than rivers, rainfall or calendars, could be used to determine the seasons. In their study, published in the journal Nature Communications in October 2020, the Stanford researchers discovered our bodies seem to set their own rhythm, splitting the year into two seasonal time periods. Or at least that’s the case if you live in California, where the study was carried out. Since every geographical location has unique environmental conditions, their approach may be used the count the seasons in other parts of the world too.

“People say there are four seasons of three months each. But why four? There could be 15 or could be 2. Why don’t we let biology tell us?” asks Prof Michael Snyder, principal investigator of the study.

To determine the human seasons, Snyder’s team profiled the biology of 105 volunteers in the San Francisco Bay area over a period of four years. They regularly sampled and measured tens of thousands of molecules and microbes from the participants’ blood, noses and guts. This type of study is called ‘deep longitudinal multiomics profiling’.

On sample days, the researchers also collected meteorological data (such as air temperature and solar radiation) and airborne pollen counts.