This research result is noted because it stands in opposition to the present consensus on vitamin D and long term health in humans; the evidence to date supports a correlation between higher levels of vitamin D, a lower risk of age-related disease, and a longer life expectancy. But here we see the opposite result. This sort of outright contradiction is usually indicative of some greater complexity under the hood yet to be outlined and understood - and there's certainly no shortage of complexity in metabolism:
Low levels of 25(OH) vitamin D are associated with various age-related diseases and mortality, but causality has not been determined. We investigated vitamin D levels in the offspring of nonagenarians who had at least one nonagenarian sibling; these offspring have a lower prevalence of age-related diseases and a higher propensity to reach old age compared with their partners.
We [assessed] vitamin D levels, [dietary] vitamin D intake and single nucleotide polymorphisms (SNPs) associated with vitamin D levels. We included offspring (n = 1038) of nonagenarians who had at least one nonagenarian sibling, and the offsprings' partners (n = 461; controls) from the Leiden Longevity Study.
The offspring had significantly lower levels of vitamin D (64.3 nmol/L) compared with controls (68.4 nmol/L), independent of possible confounding factors. ... Compared with controls, the offspring of nonagenarians who had at least one nonagenarian sibling had a reduced frequency of a common variant in the CYP2R1 gene, which predisposes people to high vitamin D levels; they also had lower levels of vitamin D that persisted over the 2 most prevalent genotypes. These results cast doubt on the causal nature of previously reported associations between low levels of vitamin D and age-related diseases and mortality.