March 27, 2014

Vitamin D and Parkinson's: Importance of Early Intervention

I’ve written before about the association that studies have suggested between Parkinson’s disease and low vitamin D levels.

A new study that investigated the levels of vitamin D in PWPs (people with Parkinson’s) suggests that early intervention with the vitamin might delay or even prevent the onset of cognitive impairment and depression. This new analysis -- published in a recent issue of the Journal of Parkinson’s Disease – is the result of an “add-on” to an ongoing longitudinal study of PWPs.

All 286 PWPs in the study were given a battery of tests measuring global cognitive function, verbal memory, semantic verbal fluency, executive function, and depression. That same day, researchers also measured the subjects’ serum 25-hydroxyvitamin D levels.

The cognition tests revealed that 61 of the 286 patients were considered demented, based on the Diagnostic and Statistical Manual of the American Psychiatric Association (4th edition). The other 225 were not.

For Undemented Subject, Better Cognition with more Vitamin D
For all subjects, scientists found significant associations between vitamin D levels and disease severity (measured by the Hoehn and Yahr Scale and the United Parkinson's Disease Rating Scale motor section). The undemented participants showed slightly higher vitamin D3 levels. (D3 is the active form of vitamin D produced by skin.)

Data for the entire group also showed association between vitamin D3 levels and greater fluency for naming vegetables and animals and immediate and delayed recall on a verbal learning test. More interestingly, for the undemented subjects only, there was significant correlation between D3 levels on the one hand and fluency and verbal learning on the other.

Dr. Amie L. Peterson of the Oregon Health and Sciences University summarized what may be the key finding:
The fact that the relationship between vitamin D concentration and cognitive performance seemed more robust in the non-demented subset suggests that earlier intervention before dementia is present may be more effective. We know mild cognitive impairment may predict the future development of dementia. Intervening in the development of dementia has the potential to improve morbidity and mortality in persons with PD.
Vitamin D and Depression
The researchers also found significant association – only among undemented subjects – between vitamin D levels and depression, an illness that often accompanies PD. There was no such correlation between vitamin levels and depression among the demented subjects, a finding that reinforces Peterson’s message about the potential for early vitamin D intervention.

Like all studies, this one has its flaws. Astonishingly, researchers did not take into account whether subjects were taking vitamin D supplements.

And while they can claim the evidence shows associations, study authors can’t demonstrate cause and effect; it’s not certain whether vitamin D deficiency is a risk factor for PD, or if PD somehow depletes vitamin D. Or, perhaps subjects with more advanced PD – and therefore less ambulatory – are simply not getting enough sunshine, an important source vitamin D.

Dr. Peterson's study concerns only people with Parkinson's, a limited group of subjects whose brains exhibit typical PD features -- dopamine depletion, neuron deterioration, etc -- not present in healthy brains. She draws different conclusions about vitamin D's effect on depression for the two groups. For PWPs, she writes, "It appears that there may be a relationship between vitamin D and cognition and mood in persons with Parkinson’s." For everyone else, she adds, "In persons without Parkinson’s disease, some research suggests vitamin D may be related to mood and cognitive function . . . however, a definitive conclusion has not been drawn."

Her reservations about a possible link between vitamin D and depression in healthy people are reinforced by new research -- published in the journal  Psychosomatic Medicine -- that found no evidence that vitamin D supplements mitigate depression in healthy people.

How Does Vitmain D Work?
Scientists can’t say exactly how vitamin D might lower the risk – or treat – Parkinson’s and its symptoms. But they do know that all cells in the human body – including neurons – have vitamin D receptors (VDRs), that VDRs control the expression of many genes or how genetic material is used, and that those important VDRs are activated by calcitriol, the active form of vitamin D.

Animal studies suggest that vitamin D protects the brain and central nervous system, an effect of particular interest in the case of Parkinson’s.

There’s another PD – vitamin D connection. Scientists have confirmed that vitamin D plays a role in bone health . . . and that PWPs have bone densities that are typically lower than in people without PD.

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There’s a mountain of research about the possible connection between vitamin D and Parkinson’s. Here’s just a sampling:
I’ve written about vitamin D on the blog before:

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