Tuesday, 19 February 2013

Should we all be getting more sun?


Interdependence and contributions of sun exposure and vitamin D to MRI measures in multiple sclerosis. Zivadinov R, Treu CN, Weinstock-Guttman B, Turner C, Bergsland N, O'Connor K, Dwyer MG, Carl E, Ramasamy DP, Qu J, Ramanathan M. J Neurol Neurosurg Psychiatry. 2013 Feb 5. [Epub ahead of print]

PURPOSE: To assess the relationships of sun exposure history, supplementation and environmental factors to vitamin D levels in multiple sclerosis (MS) patients and to evaluate the associations between sun exposure and MRI measures.
METHODS: This study included 264 MS patients (mean age 46.9±10 years, disease duration 14.6±10 years; 67.8% relapsing-remitting, 28% secondary progressive and 4.2% primary progressive MS) and 69 healthy controls. Subjects underwent neurological and 3 T MRIexaminations, provided blood samples and answered questions to a structured questionnaire. Information on race, skin and eye colour, supplement use, body mass index (BMI) and sun exposure was obtained by questionnaire. The vitamin D metabolites (25-hydroxy vitamin D3, 1, 25-dihydroxy vitamin D3 and 24, 25-dihydroxy vitamin D3) were measured using mass spectrometry.
RESULTS: Multivitamin supplementation (partial correlation r(p)=0.29, p<0.001), BMI (r(p)=-0.24, p=0.001), summer sun exposure (r(p)=0.22, p=0.002) and darker eye colour (r(p)=-0.18, p=0.015) had the strongest associations with vitamin D metabolite levels in the MS group. Increased summer sun exposure was associated with increased grey matter volume (GMV, r(p)=0.16, p=0.019) and whole brain volume (WBV, r(p)=0.20, p=0.004) after correcting for Extended Disability Status Scale in the MS group. Inclusion of 25-hydroxy vitamin D3 levels did not substantially affect the positive associations of sun exposure with WBV (r(p)=0.18, p=0.003) and GMV (r(p)=0.14, p=0.026) in the MS group.
CONCLUSIONS: Sun exposure may have direct effects on MRI measures of neurodegeneration in MS, independently of vitamin D.
To me, this study highlights one of the problems with examining vitamin D levels in people with MS in order to provide evidence about causation and/or prognosis - we really need to know what the vitamin D levels were pre-diagnosis. Vitamin D levels fluctuate from month to month, and your level now is not a good indication of what your level was months or even years ago. 

Whilst the association of sun exposure with MRI measures of MS is interesting, this study does not tell us whether this is a direct effect of the sun, or a result of something that is a common link between the sun and MS (could be vitamin D, alternatively this could be ice-cream consumption!). There are ways of measuring long-term skin exposure to sunlight, but to work out whether there is a effect of sun exposure over and above the generation of vitamin D, what we really need is a measure of long-term vitamin D status.

10 comments:

  1. Jeez - How can one imply a lack of causality or prognosis from :"Sun exposure may have direct effects on MRI measures of neurodegeneration in MS, independently of vitamin D."

    I humbly feel that you missed the mark on this one.
    The article is merely comparing D3 to direct sun exposure.

    I don't think you are giving this piece the attention it deserves, and would love to read G, MD or Ram's opinion on this one.

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    1. Thanks - always good to hear people who don't agree! Maybe I wasn't clear - I'm not saying that there definitely isn't a lack of causality, more that it is difficult to compare sun exposure over 2 years to a single vitamin D measurement. The result is certainly interesting, I wouldn't disagree with that at all, but my personal opinion is that more work is needed in terms of prospective studies so that we can tease out the effects of both vitamin D and sunlight exposure.

      I look forward to hearing what others think!

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    2. "could be vitamin D, alternatively this could be ice-cream consumption!"

      Illuminating conclusion.

      How long would you recommend the study designer's to run it for?
      Why not commenting your view on the patient/day variable than just the length of study? (264 patients is no small feat).

      Let's try to intellectually dwell over articles rather than shooting them down with Ice-cream analogies(anything else is intellectual arrogance).

      How about this view: Partially substantiated evidence that sun exposure is more beneficial to MSers than pills. Book yourself a sunny weekend at least once a month in the winter if you have the means.

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    3. oh, get off Ruth's back. The ice cream comparison has been used on this blog by many. If you're so interested in VitD go to the Australian MS reseach site, they are having a trial going comparing Vit D and sun rays.

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    4. To me, the main conclusion is *not* that sun exposure is more beneficial than pills, more that sun exposure may work in a different way to vitamin D supplementation. To me, this study begs more questions than it answers though!
      If sun exposure acts independently of vitamin D (as the authors conclude) then we need more work to try to figure out why this might be, and that is what this study doesn't address. There are possibly better ways of measuring sun exposure than in this study - the Australians have developed a way of objectively measuring actinic damage to skin (i.e. lifelong skin damage caused by sun exposure). Whilst these don't answer the question regarding mechanism, they provide the most reliable clue as to long term sun exposure. As Anon says - this is an area that the Australians are very interested in.
      The single vitamin D measurements made in this study (in which the participants were 15 years into their MS) I really don't think can be interpreted with any certainty as to a measure of the long-term vitamin D status.
      What would I do - well, I think measuring vitamin D levels repeatedly over time (could be done at the same time as MRI scans, measuring actinic skin damage (as opposed to a questionnaire) together with repeated MRI scans and looking at the relationship between changes in MRI from start to end compared to both changes in vD from start to end and skin damage as a measure of lifetime sun exposure would be interesting!

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  2. Heat intolerance is common in MS and greatly affects the ability to be out in the sun. Is heat intolerance associated with MRI measures of MS? It could be a confounding variable.

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    1. Good question, as fair skinned auburn haired have always had to avoid the hottest days, wear a hat sit in the shade or under a parasol.
      Got my Vit D levels up from 75 to 240 last year using a Veggy supplement, as tried D3 which being made from Lanolin I could not tolerate. Can only hope it has done some good, who knows. Time.
      on MRI last Sept I can see just one lesion, nothing to compare as 15 years since last MRI.

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    2. Good question Maren, and I don't think anyone has looked at that! You are right - there are many potential confounding variables, and that is why i think this study raises questions that are interesting avenues to pursue.

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    3. There's an interesting study on sun exposure and MS in monozygotic twins:
      http://www.neurology.org/content/69/4/381.short

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  3. Cyndi The D3 is not from lanolin it is from irradiated 7-Dehydrocholesterol extracted from the oils on wool. Animals with thick fur/wool cannot make vitamin d in their skin, as the skin is covered and so make it on their fur and ingest it by licking. This is however the same process as occurs in your skin. It is likely that you react to the carrier oil or coatings used to make the capsule. You can always apply it to your skin instead. There is no point in none midday sun exposure, a few moments at midday will at least make some vitamin d after 2:00pm you are only damaging your skin.

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