CHILDREN of older fathers and grandfathers are more likely to live longer, research suggests.
Experts found that children with older fathers had longer "telomeres", which are tiny caps on the ends of chromosomes that protect against ageing processes.
Like the tabs on the end of shoe laces which prevent fraying, these vital strips of DNA make cells less vulnerable to disease.
Professor Christopher Kuzawa, an anthropologist at Northwestern University in the United States, said in most cells telomeres shorten with time.
However, in sperm they lengthen. So, men who reproduce at an older age have children with longer telomeres compared with younger fathers.
Older fathers are often blamed for passing on genetic mutations to their children, causing some forms of autism, schizophrenia and other disorders.
The researchers measured the telomere length of DNA in the blood of 1,779 young Filipino adults and their mothers and determined the ages of the children's fathers and grandfathers.
They found an individual's telomeres lengthened not only with their father's age at their birth, but also with their paternal grandfather's age at their father's birth. This shows the effect is amplified over the generations – the paternal grandfather's age is associated with longer telomeres in his grandchildren.
The increase per year of a man's delay in reproduction roughly equalled the amount of annual telomere shortening observed in middle-age adults.
The findings published in Proceedings of the National Academy of Sciences suggest delayed paternal reproduction can lead to cumulative, multi-generational increases in telomere length in descendants – which could promote long life.
Telomeres have been called the "chromosomal clock" because they seem to be central to biological ageing. Longer telomeres are a sign of being biologically younger and healthier.
Prof Kuzawa said: "Although it is well established telomere length shortens with age in most proliferating tissues sperm is an exception – older men have sperm with longer telomeres.
"This may be explained by the fact the activity of telomerase – an enzyme that extends telomere length – is high in testes.
"Consistent with the fact offspring inherit half their chromosomes from sperm, offspring of older fathers tend to have longer telomeres."
In contrast telomere length in female reproductive cells in the womb are believed to be stable with age and there is no evidence for a maternal effect in offspring.
Prof Kuzawa said: "In this large sample from the Philippines, we found that telomeres measured in blood were longer in individuals whose paternal grandfathers were older at their father's birth.
"This effect was equal in size, and additive to, the longer telomere length predicted by a delay in the father's age at their own birth, suggesting that paternal age at reproduction has effects on telomere length that are transmitted with high fidelity and cumulatively across at least two generations.
"The longer telomere length predicted by each year that paternal or grandpaternal reproduction was delayed was comparable to the yearly shortening in telomere length seen in older individuals in this population, suggesting that these intergenerational changes may be biologically important.
"These findings point to a mechanism by which shifts in the age of paternal reproduction within a population can lead to cumulative, multigenerational changes in telomere length in descendants."
A previous study of over sixties found those in the top half of the range of telomere lengths lived four to five years longer than those in the bottom half.
People with shorter telomeres had a threefold increased risk of dying from heart disease and were over eight times as likely to die from infection.
Prof Kuzawa said his team's finding could be a mechanism by which humans could extend late-life function as average age at reproduction is delayed within a lineage.
He said: "We speculate an effect of the age of paternal ancestors on telomere length could allow increases in life expectancy under demographic conditions of low mortality and delayed reproduction, when investment in a more durable and long-lived body is likely to reap higher fitness returns."