A new study published in the Canadian Medical Association Journal reports that offspring who have parents living past 90 years of age (nonagenarians) have lower vitamin D levels than their spouses.
You may have seen this study covered by the media in a few places:
While there may be a study or two that cast doubts on higher vitamin D levels, this is probably not one of them. We’ll explain.
The Leiden Longevity Study is a population of 421 families, consisting of nonagenarian (over the age of 90) white siblings, their offspring, and their offspring’s partners. Researchers gathered this study population to attempt to identify genetic and phenotypic (physical characteristics) markers related to longevity.
Families were only included if at least 2 nonagenarian siblings were still alive. Since it is difficult to match controls to people of this old of age, offspring were asked to participate because they have a propensity to reach that older age. And furthermore, researchers have the benefit of matching the offspring to spouses, who usually match well in age, BMI and exposures. Researchers are likely using these families to study and publish many findings, not just on vitamin D levels and vitamin D genetics.
In this study, the researchers, led by Raymond Noordam MSc and colleagues of Leiden University Medical Center, found that offspring of nonagenarians had a vitamin D level 25.7 ng/ml, while the offspring’s partners had levels of 27.4 ng/ml. When they excluded supplement users from the analysis, the levels remained nearly the same. When they adjusted for tanning exposure habits, the difference between the offspring and partners levels still stayed nearly the same.
Keep in mind that while the difference between 25.7 ng/ml and 27.4 ng/ml is very small, particularly at the individual level, this may be significant when examining a large population. The inference here is that even if you exclude supplement users and adjust for tanning, there may be something going on genetically. Something about the nonagenarians’ offspring’s’ genetics might cause their levels to be slightly lower than their spouses.
From here, we can’t infer much else, and it doesn’t squelch the idea that vitamin D reduces mortality and thus increases longevity. There is little in the study that suggests that low vitamin D levels are the key to offspring reaching their parent’s age. There is little in the study that suggests that the nonagenarians reached that age because they have lower vitamin D levels.
There is little to suggest that if you supplement with vitamin D, you reduce your chance of living ‘til the age of 90. There is little to suggest that if you sunbathe, you reduce your chance of living ‘til the age of 90.
There is little in the study that suggests that vitamin D levels are even central to longevity. It could well be the case that there is some other gene crucial to longevity that is merely associated with genes that disposes a person to have slightly lower vitamin D levels. In other words, if all offspring and all spouses supplemented with the same amount of vitamin D, there could still likely be a difference of 1-2 ng/ml between the two groups. And this study still very much leaves room for the possibility that both the offspring and spouse would be better off raising their vitamin D levels via supplementation or exposure.
In conclusion, if you took the study for face value, it is not offering much insight into vitamin D. Even if it had found the opposite, that offspring had slightly higher levels than their spouses, there still would be little to conclude with the same set of questions remaining. That being said, there are also a few flaws and assumptions in the study:
Again, this study does not contribute much to the literature on vitamin D and does not answer the question, what level is going to get me to the age of 90? And I don’t beleive the researchers are trying to answer that question either. The study is interesting, but not insightful.
The best evidence to date that looks at mortality (the opposite of longevity) and the use of vitamin D supplementation in an elderly population was a systematic review published in the distinguished Cochrane Database. Professor Goran Bjelakovic and colleagues analyzed fifty randomized controlled trials and found that vitamin D3 supplementation decreases mortality in elderly women who are mainly in institutions and dependent care. We blog on that study here.