It's pretty hard to miss the connection between a man's testosterone level and his virility. The connection that is often missed is the connection between testosterone and man's risk of developing dangerous chronic medical conditions such as diabetes, heart disease, and obesity. A recent study suggests the level of testosterone his body produces in adulthood may be determined while he's still in the womb.

Richard Sharpe, a professor at Scotland's University of Edinburgh Medical Research Council Centre for Reproductive Health led the study, which was published in an April 2014 issue of PNAS, the weekly journal of the National Academy of Sciences of the United States of America.

Sharpe's study focused on Leydig cells, the cells in the testes that produce testosterone. Leydig cells aren't fully developed until a male child reaches puberty, at which time the cells themselves become mature enough to produce the hormone.

Previous research indicates the fully mature Leydig cells begin as a specific group of stem cells clustered in the testes of developing male fetuses. These Leydig-specific stem cells are found in the fetal testes of mammals other than humans, including marmosets, mice, and rats. Sharpe's study, involving male mice, explored the effect environmental toxins and reduced exposure to testosterone in the womb might have on the mature male.

During gestation, some of the male mice were exposed to reduced levels of androgens (male hormones, including testosterone). Others were exposed to dibutyl phthalate, an environmental toxin used in the manufacture of plastics, adhesives, printing ink, solvents, and pesticides. Phthalates are hormone disruptors that produce an estrogen-like effect in the body. The hormone-disrupting effect of phthalates is especially alarming during fetal development and during infancy and the first few years of life.

Sharpe's research team discovered the mice exposed to reduced androgens and those exposed to the phthalates had about 40% fewer Leydig stem cells at birth. Furthermore, upon reaching sexual maturity, the testosterone levels of the male mice measured in the low-to-normal range and they had elevated levels of luteinizing hormone. Luteinizing hormone, secreted by the pituitary gland, aids in androgen synthesis in males and it stimulates ovulation in females.

Of the findings of his research, Sharpe says, "There is increasing evidence that a mother’s diet, lifestyle and exposure to drugs and chemicals can have a significant impact on testosterone levels in the womb. We need a better grasp of these factors so that we can give reliable advice to pregnant women to protect the health of her unborn child.

Source: Sharpe, Richard M. "Fetal programming of adult Leydig cell function by androgenic effects on stem/progenitor cells." PNAS. National Academy of Sciences. Apr 21, 2014. Web. May 1, 2014.