Men who want to become fathers adjust their testosterone levels to make conception more likely, according to new research.

Katharina Hirschenhauser, an expert in sex hormones, and her team at the Institute of Applied Psychology in Lisbon, Portugal, set out to see if there was any link between men’s testosterone levels and their sexual behaviour.

They asked 27 volunteers to measure the testosterone in their saliva every morning for 90 days. Over the same period, the men also recorded their sex lives in intimate detail, documenting the “intensity” of each encounter, whether with their regular partner or not.

All the men had different patterns of testosterone peaks and troughs over the period. But in men trying for a baby, peaks in testosterone levels coincided far more often with periods of intense sexual activity. Hirschenhauser says the finding shows men can subconsciously influence their hormone levels. “Males can be responsive to their partners, but only if they want to be,” she says.
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