A new study at the Weizmann Institute of Science reveals that our hormones also follow a seasonal pattern. By analyzing the data on several kinds of hormone from millions of blood tests, the researchers discovered that some hormones peak in winter or spring, and others in summer. This research, which was published in the Proceedings of the National Academy of Sciences (PNAS), USA, provides a broad, dynamic picture of hormone production – covering those connected, for example, to fertility, but also hormones such as cortisol, which are mostly short-lived and not thought to be seasonal.
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Alon Bar led the study together with Avichai Tendler; both are research students in Professor Uri Alon's group at the Institute's Molecular Cell Biology Department.
The team analyzed the hormone levels in males and females between the ages of 20 and 50, in millions of blood tests sorted according to the months of the year. The researchers tracked 11 different hormones, including cortisol (a stress hormone released by the adrenal glands), a thyroid hormone, reproduction and sex-based hormones and a growth hormone produced in the liver.
On average, all of these hormones exhibited peaks and dips over the year with a seasonal variation of around 5%, but the surprise was the ways in which certain ones peaked at different times. For example, the hormones testosterone and estradiol – one more prevalent in men, the other in women – were mirror images of one another. So the fact that more children are conceived in certain seasons may have more to do with hormone balances than the blooming of flowers in the fields, says Bar.
