At medical school we learned about the role that vitamin D has in bone
metabolism, including its transformation from a less active form made by the
kidneys to the more active form, which requires adequate sunlight on the skin.
Low levels would lead to rickets in children, and osteomalacia in adults. Northern
climes were associated with fair skin to allow more of the active vitamin D to
be made in the ‘weaker’ sunshine, and that between October and March, even the
fairest skinned amongst us would be unable to get enough natural sunshine (I
was at medical school in Sheffield).
Since then however, there seems to have been some “mission creep”.
Vitamin D now has been associated with countless conditions that seem to have
nothing to do with calcium and phosphate turnover. Low levels are associated
with worse response to TB treatment; vitamin D supplements are given in the
community to people with non-specific aches, pains and low levels of
depression; low vitamin D increases your risk of stroke and heart attack.
The brain diseases are involved too. People with MS are exhorted to
take on extra vitamin D; low vitamin D levels are associated with a higher
incidence of dementia. There is clearly much we have to learn about this
intruiging compound, and its functions are clearly much more complex than has previously
been thought.
What about Parkinson’s disease? There are several ongoing studies of
prodromal Parkinson’s disease – research identifying people who have the
underlying process that causes PD, but haven’t yet developed the full motor
manifestations that are necessary for the clinical diagnosis. PREDICT-PD is one
(and although we are partial, we think it's the best one), but the PRIPS study
in Europe and the PARS study in North America are also very well designed
studies that are reporting key discoveries in the fight against Parkinson’s.
An article this week reported on the levels of vitamin D in
participants of the PARS study. The authors compared those thought to be at
high risk of PD based on poor smell and abnormal DaT scans (a kind of brain
scan that looks at dopamine transporters) and found no differences between the
two groups.
At the moment, therefore, there is no justification for recommending
taking vitamin D supplements to reduce your risk of PD. On the other hand, as
many of our blog posts have highlighted, getting out and about, and doing some exercise
in the sunshine, or even taking a nice holiday to escape the brisk British
November greyness, might well do you good!
RNR
https://www.ncbi.nlm.nih.gov/pubmed/28984598
J Alzheimers Dis. 2017;60(3):989-997.
doi: 10.3233/JAD-170407.
Vitamin D and the Risk of Dementia:
The Rotterdam Study.
Abstract
BACKGROUND:
Vitamin D has gained interest as a potentially
modifiable risk factor for dementia because of its putative
neuroprotective effects. However, longitudinal studies examining the
association between vitamin D and dementia have provided
inconsistent results.
OBJECTIVE:
To determine the relationship of serum vitamin D with
prevalent and incident dementia in the general population.
METHODS:
Within the prospective Rotterdam Study, we measured serum
25-hydroxyvitamin D concentrations between 1997 and 2001 using
electrochemiluminescence-immunoassay in 6220 participants 55 years or older. We
assessed dementia at baseline and continuously during follow-up until
1 January 2015. We used appropriate regression models to determine the
relationship of vitamin D with prevalent and incident dementia,
including Alzheimer's disease (AD). We adjusted models for age, sex, and season
of blood collection. Additionally, we adjusted for ethnicity, education,
cardiovascular risk factors, serum calcium, kidney function, depression,
outdoor-activity and APOEɛ4 carriership.
RESULTS:
At baseline, 127 of 6,220 participants had dementia, of
whom 97 had AD. Lower vitamin D concentrations were associated with a
non-significantly higher prevalence of dementia (adjusted OR, per SD
decrease 1.20, 95% CI 0.95;1.52), but not with AD (adjusted OR: 0.97, 95% CI
0.74;1.29). Among 6,087 non-demented participants with 68,884 person-years of
follow-up, 795 participants developed dementia, of whom 641 had AD.
Lower vitamin D concentrations were associated with higher risk
of dementia (adjusted HR, per SD decrease 1.11, 95% CI 1.02;1.20) and
AD (adjusted HR: 1.13, 95% CI 1.03;1.24).
CONCLUSION:
Lower serum vitamin D concentrations are
associated with a higher incidence of dementia.
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