Saturday, 23 August 2014

Low vitamin D levels linked to dementia

Are Alzheimer's dementia and MS a consumptive hypovitaminosis D? #MSBlog #MSResearch

"Some of you may have heard about the study below showing a link between low vitamin D levels and the development of dementia, in particular Alzheimer's disease."

"Deja vu? This could have been an MS study. Does it mean vitamin D deficiency is a cause of Alzheimer's disease? Definitely not, causation theory requires many more boxes to be ticked. All we can say that there is an association between vD deficiency and the development of dementia. One could hypothesise that predementia causes low vD levels. Similar to MS, there is a long presymptomatic prodrome of years, or even decades, to the onset of clinically-defined dementia. Maybe the processes that underlie the development of dementia are consuming vD and therefore depressing circulating levels. The so called consumptive hypovitaminosis D hypothesis."

"Maybe people who are in the phase of pre-dementia change their behaviour with less outdoor activity and hence get less sunlight exposure. There is some evidence for the latter; people with early dementia are more likely to become socially-isolated and socially excluded. Could people with pre-dementia change their diet and eat less foodstuffs with vD? Could people with predementia to be less likely to taking vD supplements? If they did buy supplements are less likely to take them; i.e. forget to take them?"

"What this observation tells us that more work needs to be done including a vD dementia prevention study. I am aware that vD supplementation prevention studies are under way in oncology, for example prostate cancer, hopefully these studies can be adapted to look at dementia onset as well. What still needs to ascertained is what dose of vD supplementation to use? Do you treat to target of a specific vD level? Do you use population normative data to define what is a normal vD level, as we do now? Or do we use a evolutionary medicine approach and set normal levels from populations living pre-industrial outdoor lifestyles? I favour the latter and if we do go this route then we really need to keep our vD levels above 100nmol/L. This is the vD level of nomadic outdoor hunter-gatherer peoples. Some critics would argue that this is missing the point and that low vD levels are simply a proxy for low sunlight exposure and  that what we really need is a healthy dose of daily sunshine. They may be right; there is evidence that UV light to the skin modulates immune function by the effects of UV light on lymphocyte function. In fact there is an immune therapy based on this."

"Clearly the vD field has more questions than answers. What is clear is that they need answering and answering soon. We can't let the next generation down by not trying to do good science and answer these questions in the next 5-10 years."

Is it low vD or too little sunlight exposure that is important? Will we ever know the answer?

Epub: Littlejohns et al. Vitamin D and the risk of dementia and Alzheimer disease. Neurology. 2014 Aug 6. pii: 10.1212/WNL.0000000000000755.

OBJECTIVE: To determine whether low vitamin D concentrations are associated with an increased risk of incident all-cause dementia and Alzheimer disease.

METHODS: One thousand six hundred fifty-eight elderly ambulatory adults free from dementia, cardiovascular disease, and stroke who participated in the US population-based Cardiovascular Health Study between 1992-1993 and 1999 were included. Serum 25-hydroxyvitamin D (25(OH)D) concentrations were determined by liquid chromatography-tandem mass spectrometry from blood samples collected in 1992-1993. Incident all-cause dementia and Alzheimer disease status were assessed during follow-up using National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association criteria.

RESULTS: During a mean follow-up of 5.6 years, 171 participants developed all-cause dementia, including 102 cases of Alzheimer disease. Using Cox proportional hazards models, the multivariate adjusted hazard ratios (95% confidence interval [CI]) for incident all-cause dementia in participants who were severely 25(OH)D deficient (<25 nmol/L) and deficient (≥25 to <50 nmol/L) were 2.25 (95% CI: 1.23-4.13) and 1.53 (95% CI: 1.06-2.21) compared to participants with sufficient concentrations (≥50 nmol/L). The multivariate adjusted hazard ratios for incident Alzheimer disease in participants who were severely 25(OH)D deficient and deficient compared to participants with sufficient concentrations were 2.22 (95% CI: 1.02-4.83) and 1.69 (95% CI: 1.06-2.69). In multivariate adjusted penalized smoothing spline plots, the risk of all-cause dementia and Alzheimer disease markedly increased below a threshold of 50 nmol/L.

CONCLUSION: Our results confirm that vitamin D deficiency is associated with a substantially increased risk of all-cause dementia and Alzheimer disease. This adds to the ongoing debate about the role of vitamin D in nonskeletal conditions.

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