By Michelle Roberts Health editor, BBC News website
Delaying fatherhood may offer survival advantages, say US scientists who have
found children with older fathers and grandfathers appear to be "genetically
programmed" to live longer.
The genetic make-up of sperm changes as a man ages and develops DNA code that
favours a longer life - a trait he then passes to his children.
The team found the link after analysing the DNA of 1,779 young adults.
Their work appears in Proceedings of the National Academy of Sciences.
Shoe lace tips
Experts have known for some time that lifespan is linked to the length of
structures known as telomeres that sit at the end of the chromosomes that house
our genetic code, DNA. Generally, a shorter telomere length means a shorter
life expectancy.
Like the plastic tips on shoelaces, telomeres protect chromosomal ends from
damage. But in most cells, they shorten with age until the cells are no longer
able to replicate.
However, scientist have discovered that in sperm, telomeres lengthen with age.
Telomeres (in red) cap chromosomes Telomeres (in red) cap the ends of
chromosomes
And since men pass on their DNA to their children via sperm, these long
telomeres can be inherited by the next generation.
Dr Dan Eisenberg and colleagues from the Department of Anthropology at
Northwestern University studied telomere inheritance in a group of young people
living in the Philippines.
Telomeres, measured in blood samples, were longer in individuals whose father's
were older when they were born.
The telomere lengthening seen with each year that the men delayed fatherhood
was equal to the yearly shortening of telomere length that occurs in
middle-aged adults.
Telomere lengthening was even greater if the child's paternal grandfather had
also been older when he became a father.
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Very few of the studies that linked telomere length to health in late life have
studied the impact, if any, of paternal age
Prof Thomas von Zglinicki Professor of Cell Gerontology
Although delaying fatherhood increases the risk of miscarriage, the researchers
believe there may be long-term health benefits.
Inheriting longer telomeres will be particularly beneficial for tissues and
biological functions that involve rapid cell growth and turnover - such as the
immune system, gut and skin - the scientists believe.
And it could have significant implications for general population health.
"As paternal ancestors delay reproduction, longer telomere length will be
passed to offspring, which could allow life span to be extended as populations
survive to reproduce at older ages."
Prof Thomas von Zglinicki, an expert in cellular ageing at Newcastle
University, said more research is needed.
"Very few of the studies that linked telomere length to health in late life
have studied the impact, if any, of paternal age. It is still completely
unclear whether telomere length at conception (or birth) or rate of telomere
loss with age is more important for age-related morbidity and mortality risk in
humans.
"The authors did not examine health status in the first generation offspring."
It might be possible that the advantage of receiving long telomeres from an old
father is more then set off by the disadvantage of higher levels of general DNA
damage and mutations in sperm, he said.