Testosterone speeds male babies' growth

Males who experience rapid growth as babies are taller, have more muscle and also higher testosterone levels as young adults.

The researchers believe that testosterone may hold the key to understanding these long-term effects and that genes alone do not shape our fate.

"Most people are unaware that male infants in the first six months of life produce testosterone at approximately the same level as an adult male," said Christopher W. Kuzawa, study author.u00a0

"We looked at weight gain during this particular window of early life development because testosterone is very high at this age and helps shape the differences between males and females," said Kuzawa, associate professor of anthropology at Northwestern University in the US.u00a0

The study found men tend to be taller and more muscular than females and the magnitude of that difference appears to be the result of nutrition within the first six months of an infant male's life, according to a Northwestern statement.u00a0

"The environment has a very strong hand in how we turn out. And this study extends that idea to the realm of sex differences and male biology," Kuzawa said.u00a0

"In the last 20 years, a lot has been learned about a process called developmental plasticity -- how the body responds early in life to things like nutrition and stress," he added.

Early experiences can have a permanent effect on how the body develops and this effect can linger on to adulthood.

"There is a lot of evidence that this can influence risk of diseases like heart attack, diabetes and hypertension," Kuzawa said.u00a0

Kuzawa and his collaborators applied the same framework in this study and found evidence that male characteristics -- such as height, muscle mass and testosterone levels as opposed to disease characteristics are linked to body's response to nutrition and stress.

"Another way to look at it is that the differences between the sexes are not hard wired but are responsive to the environment and in particular to nutrition," Kuzawa said.u00a0

Testosterone has long been known to increase muscle mass and puts a person on a higher growth trajectory to be taller. The Northwestern study suggests that the age of puberty is also influenced by events in the first six months of life.

The study is based on a group of 770 Filipino males aged 20-22 who have been followed their entire lives.