Without male hormone receptors to respond to testosterone, the researchers started to suspect androgen receptors were not the players they had been assumed to be.

ECONOMIST: Behaviour of the sexes

"I'm just amazed how many men start a hormone without doing research, " he says.

CNN: Baby boomers find youth in testosterone

But glucose can't enter our cells without insulin, which is a hormone produced by the pancreas.

CNN: Reversing diabetes is possible

The hormone will help you lose weight and build muscle, but not without proper exercise and nutrition.

CNN: Baby boomers find youth in testosterone

Observing 25 infants aged 4 to 10 months in a five-day inpatient sleep training program, researchers monitored levels of the stress hormone cortisol in the babies, who were left to cry themselves to sleep without being soothed.

CNN: Should babies be allowed to 'cry it out'?

The hormone-exposure theory suggests that women with twin brothers should more often be homosexual than those without.

ECONOMIST: Homosexuality