In general, regardless of age group 40-49yo, 50-59yo & >60yo, their average 25OH vitamin D was just over 15ng/mL or well into the deficient range. Of course, the definitions of normal, insufficient & deficient are open to debate. Suffice it to say that those w/25OH vitamin <10ng/mL had a significantly higher all-cause mortality compared to those whose level is >21ng/mL. However, lowest mortality was found at >35ng/mL.
Of course the big question that needs to be addressed is whether the chicken or the egg came first. Remember that this was a prospective cohort study, not a randomized controlled trial. This doesn't prove anything but rather proposes hypotheses that need to be sorted out. Perhaps, all-cause mortality is lower in those w/greater vitamin D because they spend more time outdoors exercising. Hopefully time will tell. We'll see.