Girls, Pacific children and babies born to older mothers might potentially be able to live longer, thanks to a unique genetic advantage observed by New Zealand researchers.
New research, drawing on DNA samples from more than 4000 children in the country's largest longitudinal study, suggested these groups may have lengthier telomeres – an essential part of human chromosomes that are linked to ageing.
Telomeres can be compared to plastic tips on the end of shoelaces, protecting each strand of our DNA from damage, and shorten as we age, affecting the development of age-related disease.
While studies have previously drawn links between these general groups and telomeres, the new paper, published in the journal Scientific Reports, was the first time the connection had been shown in New Zealand children.
It was revealed using the Growing Up In New Zealand (GUiNZ) study, which has been tracking more than 6000 children since birth.
University of Auckland senior research fellow Dr Caroline Walker explained telomere length was a "biomarker" of biological age that had been associated with longevity.
"Your telomere length is a product of your genetic make-up but is also influenced by the environment you live in and your lifestyle choices," Walker said.
"This means we can use telomere length to understand the influence of these factors on your biological age."
While many studies had shown that issues with stress, diet and exercise could have a negative influence on telomere length in adults, few had examined telomere length in children – and those that had reported mixed results, possibly due to small sample sizes.
Walker said the size of the GUiNZ cohort meant that any differences between adults and children could be shown more clearly.
When children in the cohort were 4 years old, parents were asked to consent to their child providing saliva samples, which were packed full of white blood cells, or the cells of our immune system.
In the lab, she and colleagues extracted DNA from these cells and measured their telomere length using a method called quantitative PCR, before searching for patterns related to gender, ethnicity and parental age.
All three factors shone through.
Girls' telomeres were 4 per cent longer than boys – and by ethnicity, Pacific children had the longest telomeres, followed by Asian children, Māori children and then European children.
Children born to older mothers also had longer telomeres.
Walker said it still wasn't known exactly why females had longer telomeres than males but there were some theories.
One was that oestrogen and testosterone, respectively, had positive and negative effects on telomere length – yet that didn't explain differences in young girls and boys, as all had similar levels of both hormones at that age.
Another was that a larger body size resulted in more cell divisions, which shortened telomeres – but telomeres were still longer in females, even when differences in body size were accounted for.
A further theory was that having two X chromosomes – as girls do - resulted in longer telomeres.
"Some of the telomere maintenance genes are found on the X chromosome so having two might explain the longer telomeres in females," Walker said.
"However, if this were true we would expect differences to exist at birth and so far there has been no evidence to support this. Also, the second X chromosome in females is mostly inactivated and so theoretically shouldn't confer an advantage."
She said the study not only backed up reports that Maori and Pacific adults had longer telomeres, but proved this was also true in early life.
"We think this suggests that ethnic specific differences in telomere length are the result of genetic variation."
As for the parental factor, that was in line with a majority of studies that had linked father age to telomere length in their children.
"In most cells in our body, telomeres shorten in age but there is some evidence that in sperm, telomeres actually lengthen with age - therefore, older dads pass on longer telomeres to their children."
Despite the study's fascinating insights, it also left many more questions to answer.
For instance, she said, the study hadn't explored certain genetic factors, which, combined with lifestyle and environmental factors, largely determined telomere length at early life.
Her team were now looking at what influence various environmental and lifestyle factors had at age 4, along with the effect that body size, growth, diet and stress had.
But as for just how much more life a longer telomere equated to, Walker said it was the rate of telomere shortening, rather than initial length, that offered a better predictor of lifespan.
"This means we really need additional measures of telomere length across the lifespan to understand how New Zealand children are biologically ageing and what factors accelerate or slow down this process."
• New Zealand scientists analysed DNA samples, taken from 4000 children when they were aged 4, for patterns in their telomeres.
• Telomeres are part of our chromosomes and protect each strand of DNA from damage. They shorten as we age and can affect the development of age-related disease.
• Their study revealed girls, Pacific children and those born to older parents had longer telomeres.
• It was the first study to report for New Zealand and Pacific children. The researchers are now delving deeper for further insights.