Hot and bothered Disposable nappies increase the testicle temperature of baby boys, possibly contributing to falling sperm counts
The widespread use of disposable nappies could be contributing to the dramatic reduction in human sperm counts seen in the past 50 years, say German scientists.
The team found that the average scrotal temperature of 48 baby boys was around 1 °C higher when they were wearing disposable plastic-lined nappies, rather than reusable cotton ones.
Raising the temperature of the testes reduces sperm production in men. The scientists speculate that higher testicular temperatures in childhood could impair the development of the testes and sperm production in later life.
"This is not an unreasonable hypothesis," says Ieuan Hughes of Cambridge University. "Sertoli cells, which support the sperm-producing cells, are actively laid down and dividing during the first one to two years of life.
"And the testes produce high levels of testosterone at this time, which is certainly needed for normal sperm production in adult life."
Catastrophic fall
Studies indicate that the average sperm count of men around the world has fallen by half in the past 50 years, Hughes says. Factors such as increased environmental levels of chemicals that disrupt male hormones have been blamed. But Hughes agrees that the widespread adoption of plastic-lined nappies could also be important.
However, the study is rejected by the Absorbent Hygiene Products Manufacturers Association, which represents the disposable nappy industry. "We believe the study is scientifically unsound," says a spokesman.
"The cloth nappy was tested without the plastic pants commonly used with them. This would clearly affect the comparison of scrotal temperatures," he says.
Changing time
Wolfgang Sippell and colleagues at the University of Kiel monitored the scrotal and rectal temperatures of children aged from birth up to four and a half years of age. Readings were taken over two 24-hour periods. During one period, the babies wore disposable nappies. During the other, they wore cotton nappies.
Normal physiological cooling mechanisms keep the testes of adult men around 2.5 °C cooler than the rest of the body. Sippell's team found that in toddlers wearing cotton nappies, there was an average difference in their rectal and scrotal temperatures of 2.6 °C. But this difference was reduced in all 48 boys while they wore disposable nappies, and it disappeared entirely in 13.
This impairment of the body's normal cooling of the testes "may have a negative long-term effect on testicular maturation and spermatogenesis", the team concludes in the journal Archives of Disease in Childhood.
Disposable nappies were introduced around 25 years ago. The team now plans to compare sperm production in men born before 1990 in the former West Germany, where disposable nappies have long been popular, with those born before 1990 in East Germany, where they have only recently been adopted.
Source: Archives of Disease in Childhood (vol 83, p 364)