Sperm Quality and Age
Although there is no strong evidence that sperm suffer the same age related degradation as women's eggs undergo, older sperm do cause their fair share of genetic problems, albeit in a much different way.
In contrast to females, who are born with all their eggs, men have no sperm when they are born. They don’t make any sperm until they reach puberty, when a prolific and persistent production begins. The average man makes about 250 million sperm a day: that’s about 6,000 sperm every time his heart beats. As a man ages, sperm production continues unabated, and there is no strong clinical or scientific evidence that production decreases significantly even in 70 and 80 year old men.
Since sperm production is so high, a man has to keep copying his DNA over and over again to make sperm. All this DNA copying leads to small mistakes, called mutations. If you remember that at its most basic level, DNA is a series of letters that make up recipes called genes. If the recipe is copied millions of times a day, mistakes inevitably happen.
Imagine having a cake recipe that has 3 cups of flour as part of the text. You photocopy the recipe for a friend. She photocopies your photocopy for a friend and so on. After multiple copies, your 3 cups of flour might start to look like 2 cups of flour, and suddenly your cake recipe doesn’t work any more.
These subtle copying defects cause a long list of diseases in the children of older fathers. Lesch Nyhan Syndrome, Polycystic kidney disease and Hemophilia A are among the most well known. For fathers over age 40, the risk of having a child with a disease-causing mutation is similar to the risk the mother has for a child with Down syndrome.
The biology of eggs and the aging of ovarian reserves are relatively well understood phenomena. As people gain a better understanding of how aging sperm can contribute to fertility complications, older couples will have better tools for planning their families.