A surprising link has been found between long life spans and naturally low levels of vitamin D.
Scientists made the discovery after studying data on 380 families with members who survived into their nineties.
Previous research has shown that people lacking the "sunshine vitamin" are more at risk from a host of conditions including heart disease, diabetes, cancer, allergies and mental illness.
According to these studies, having too little vitamin D increases the chances of premature death.
Dutch scientists examined data from the Leiden Longevity Study, which involved families with at least two very elderly siblings - either a brother aged at least 89, or a sister aged 91 and over. A total of 1,038 offspring of the elderly siblings were also included, together with their partners.
Vitamin D is created in the skin by the action of sunlight, and also obtained from food or supplements, but genetic factors also influence blood levels in different individuals.
The scientists looked at the influence of genetic code alterations known as single nucleotide polymorphisms (SNPs) in three genes associated with vitamin D levels.
The authors, led by Dr Diana van Heemst, from Leiden University Medical Centre, wrote: "We found that the offspring of nonagenarians who had at least one nonagenarian sibling had lower levels of vitamin D than controls, independent of possible confounding factors and SNPs associated with vitamin D levels."
Offspring of long-lived individuals were also less likely to have a common genetic variant in a gene called CYP2R1, which predisposes people to high levels of vitamin D.
Vitamin D is known to be vital for healthy bones and teeth. But the new results throw doubt on the idea that low levels of the vitamin in the blood can lead to a wide array of health problems, according to the researchers. Previous studies have tended not to show whether low vitamin D caused disease or resulted from it, they say.
"Cross-sectional and longitudinal studies have linked low serum levels of vitamin D to a higher risk of death, cardiovascular disease and cognitive decline," the scientists wrote. "Because of limitations in the design of these studies, it was not possible to infer a causal relation between vitamin D and outcome.
"In the case of mortality, low serum vitamin D levels might be a marker of frailty, because ill patients are expected to spend less time outdoors and may have inadequate nutrition."
The new research suggested that naturally low levels of vitamin D may go hand-in-hand with a genetic resistance to ageing.
Their findings are reported in the Canadian Medical Association Journal.
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