If you follow health reporting by outlets like Salon or the New York Times, you might know that the last several years have been dark times for vitamin manufacturers. Despite about half of Americans using vitamin supplements and even the Harvard
School of Public Health recommending a daily multivitamin as a “nutrition insurance policy”—the data just hasn’t seemed to hold up. In both pooled analyses of clinical trials and direct intervention with multivitamins with clinical trials, researchers have largely failed to see any large health benefit to your daily multivitamin. Some outlets have even gone so far as to call the entire vitamin industry a scam.
But this isn’t the end of the road for vitamin supplements in general. Supplementation with individual vitamins still shows promise for reducing the threat of aging related diseases, as a groundbreaking study showing that normal vitamin D levels significantly reduce the risk of Alzheimer’s and general dementias now demonstrates.
Re-analyzing data: Double the bang for your buck!
Using a remarkably frugal approach, researchers primarily based at the University of Exeter Medical School re-analyzed samples from the 1992-1999 Cardiovascular Health Study for vitamin D levels and followed up with patients from the study to see which ones developed symptoms of dementia (the clinical term for age-related cognitive impairment, both Alzheimer’s and not).
Because the people in this study weren’t specifically selected to be at risk for any neurodegenerative disease, these patients could be considered to reflect the US population as a whole, rather than some skewed study population. And, similar to the general population of elder adults (~13%), about 10% (171 of 1,658) developed dementia. But when these patients were categorized by their blood vitamin D levels, it became clear that the most severely deficient patients (<25nmol/L) had over twice the risk of dementia due to all causes (2.25x) than patients with “adequate” vitamin D levels (around 50 nmol/L). Even patients with mildly deficient vitamin D levels (in the 25-50 nmol/L) range showed some elevated risk of dementia (1.53x)—showing that you don’t need full-blown vitamin D deficiency (along with rickets, the associated bone weakness) to increase your risk for cognitive impairment.
Where do doctors get these ideas, anyway?
In some ways, this connection isn’t surprising. Pooled analysis of data from smaller trials suggested that there may be a connection between vitamin D levels and dementia. More importantly, previous work has shown direct connections between vitamin D itself and effects in the brain–mutations in the receptor that’s necessary for the function of vitamin D (VDR) are associated with Alzheimer’s disease, and treatment with vitamin D supplements seems to reduce the symptoms of Alzheimer’s disease in mouse models.
Furthermore, unlike many other vitamins (like the B vitamins, which play structural roles and don’t matter as long as you just get enough) it’s not surprising that vitamin D could have strong, wide-ranging effects in the brain: vitamin D is a steroid hormone—it belongs to a class of molecule (the vitamin D receptor, VDR) which controls which genes are turned on in a particular type of cell. Not surprisingly, this vitamin D receptor is specifically localized to many of the regions of the brain (the hippocampus, or memory formation center) that go haywire in patients with dementia. It’s highly likely that vitamin D is necessary for turning on genes that are necessary for proper function in these brain regions, and that in the absence of adequate supplies of vitamin D, these regions of the brain become more susceptible to all kinds of insults, increasing the risk of dementia.
Wait, why does this have to do with aging?
This study is just the latest in a long line of studies that show that vitamin D levels are associated with general health in aging adults: at least one study has shown a decrease in the prevalence of *all* kinds of mortality in people who take vitamin D supplements, and an association of lower levels with increased risks of all causes of death.
The good news in all of this is that there’s no evidence that there’s some complex connection between vitamin D levels as you get older—it seems to be the case that older people are simply less able to make and assimilate vitamin D. The ability of the skin to synthesize vitamin D from its starting material seems to naturally decline with age, and certain other conditions that are associated with age like obesity can decrease the ability of the body to assimilate vitamin D from the diet. All this means that simple oral vitamin D supplements hold a great deal of promise in reducing the burden of age-related cognitive decline.