Scientists at Cambridge University found high levels of DNA mutations in the sperm cells of teenage boys, which results in a 30 percent higher risk of children with conditions such as autism, schizophrenia, and spina bifida.
The scientific explanation, researchers believe, is that the male reproductive system may not be working at optimum parameters until a few years after puberty.
According to researchers, the sperm cells of teenagers aged 12 to 19 had 30% more mutations than those of men in their 20s.
Compared to teenage woman, male cells went six times as many DNA mutations during teenage years, as the study of 24,000 parents and their children unveiled.
The research was published in the journal Proceeding of the Royal Society B.
The study noticed that men have their healthiest sperm in their 20s and early 30s, before the number of mutations start to increase as men approach their 40s.
This discovery may explain, for the first time, the increased number of birth defects in children born to teenage parents, said Dr. Peter Foster, who led the study.
Mutations occur when an error occurs during the DNA copying process taking place in cell division.
Dr Forster, who carried out the research with colleagues in Germany and Austria, said it is unclear precisely why teenage boys have more mutations than older men.
He mentioned, however, that it takes some time for the reproductive system in young adolescents to start work without fault.
“It may be that it needs a bit of a warm-up period for the system to work properly,” Dr Forster said. “Possibly the DNA copying mechanism is particularly error-prone at the beginning of male puberty.”
There is a 1.5 percent risk for an average man to father a baby with a birth defect.
In teenage boys, however, the risk is 2 percent – a significant increase, especially when one considers the populations as a whole, but quite small risk increase on an individual level.
Dr Foster added: “Most people are sensible and do not have children in their teens. And if they do, there is not much to worry about on an individual level. This also does not mean that every birth defect is caused by DNA mutation. It may be one more reason for it being best for teenage boys not to have children, but it should not be the only reason.”