日光浴が多発性硬化症を予防する

多発性硬化症の一卵性双生児に関する研究から、小児期に太陽の下で過ごす時間が長いと多発性硬化症の発症が57%低下するという。
南カリフォルニア大の以前の研究から、ビタミンDサプリを飲んでいる女性は多発性硬化症(MS)の発症率が40%低いという報告結果がある。MSは免疫系異常が関連した病気であり、高緯度地域に多発しているため、日光-紫外線が免疫賦活性ビタミンDと間接的に関連しているらしい。

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多発性硬化症 (たはつせいこうかしょう、multiple sclerosis;MS)とは Wikipedia より
中枢性脱髄疾患の一つで、脳、脊髄、視神経などに病変が起こり、多彩な神経症状が再発と寛解を繰り返す疾患である。日本では特定疾患に認定されている指定難病である。
疫学:中枢性脱髄疾患の中では患者が最も多い。北米、北欧、オーストラリア南部では人口10万人当たり30~80人ほど罹患しているが、アジアやアフリカでは人口10万人当たり4人以下で、人種によって罹患率に大きな差があることが特徴である。南米、南欧、オーストラリア北部はその中間である。日本での有病率は増加してきており、10万人あたり10人程度であることが2006年神経免疫班会議で報告されている。若い人のほうが発症しやすい。罹患のピークは30歳頃であり、約80%が50歳までに発症する。男女比は女性のほうが多いといわれる。
原因:さまざまな説はあるがいまだ原因は不明である。このうち遺伝、自己免疫、ウイルスなどの感染が可能性が高いと思われている。

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Last Updated: Saturday, 28 July 2007, 23:40 GMT 00:40 UK
Sunshine 'protective' against MS
http://news.bbc.co.uk/2/hi/health/6906712.stm

画像beach life
Some sun can be a good thing

People who spend more time in the sun as children subsequently have a lower risk of developing multiple sclerosis (MS), a US study shows.

The University of Southern California team suggest UV rays offer protection by altering the cell immune responses or by boosting vitamin D levels.
An earlier study found women who took vitamin D supplements were 40% less likely to develop MS.
The latest research is published in the journal Neurology.
Protective effect
MS is among the most common neurological diseases affecting around two million people worldwide.
However, it is more common at higher latitudes, which generally have lower levels of ultraviolet radiation - the type produced by the sun.
People in these countries are exposed to less sunlight, which triggers a chemical reaction in the body leading to vitamin D production.
For the study, researchers surveyed 79 pairs of identical twins who had the same genetic risk of MS.
In each pair, one of the twins had MS.


The researchers are certainly not suggesting people go out and get skin cancer. Exposure to the sun's rays can be dangerous
Chris Jones, chief executive of the MS Trust

The twins were asked to specify whether they or their twin spent more time outdoors during hot days, cold days, and summer, and which one spent more time basking in the sun, going to the beach and playing team sports as a child.
The researchers found the twin with MS spent less time in the sun as a child than the twin who did not have MS.
Depending on the activity, the twin who spent more hours outdoors had up to a 57% reduced risk of developing MS.
The study authors, Dr Talat Islam and Dr Thomas Mack, said more work into how sun exposure reduces MS risk was now needed.
They suggested: "Exposure to ultra violet rays may induce protection against MS by alternative mechanisms, either directly by altering the cellular immune response or indirectly by producing immunoactive vitamin D."
Chris Jones, chief executive of the MS Trust, said: "This work supports past work suggesting a link between sun exposure and a lower risk of MS.
"But the researchers are certainly not suggesting people go out and get skin cancer. Exposure to the sun's rays can be dangerous."

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NEUROLOGY 2007;69:381-388
© 2007 American Academy of Neurology
Childhood sun exposure influences risk of multiple sclerosis in monozygotic twins
Talat Islam, MBBS, PhD, W. James Gauderman, PhD, Wendy Cozen, DO, MPH and Thomas M. Mack, MD, MPH
From the Department of Preventive Medicine, University of Southern California, Los Angeles, CA.
Address correspondence and reprint requests to Dr. Thomas M. Mack, Department of Preventive Medicine, Keck School of Medicine, 1441 Eastlake Avenue, NOR 4453 Los Angeles, CA 90033 tmack@usc.edu.

Objective: To address the role of childhood sun exposure on the risk of multiple sclerosis (MS) after controlling for genetic susceptibility, we investigated the association between sun exposure and MS comparing disease-discordant monozygotic (MZ) twins.

Method: Twins with MS were sought by yearly newspaper advertisements throughout North America from 1980 to 1992. Diagnosis was verified by updated medical documentation through 2005. This analysis was restricted to 79 disease- and exposure-discordant monozygotic twin pairs who had ranked themselves before 1993 in relation to each of nine childhood sun exposure activities. A sun exposure index (SI) was defined as the sum of those exposures for which one twin ranked higher than his or her co-twin. The SI difference within each twin pair was calculated by subtracting the SI value of the affected twin from the SI value of the unaffected twin (range –9 to +9). The results were then analyzed using conditional logistic models.

Result: Each of the nine sun exposure–related activities during childhood seemed to convey a strong protection against MS within MZ twin pairs. Depending on the activity, the odds ratio (OR) ranged from 0.25 to 0.57. For example, the risk of subsequent MS was substantially lower (OR 0.40, 95% CI 0.19 to 0.83) for the twin who spent more time suntanning in comparison with the co-twin. For each unit increase in SI, the relative risk of MS decreased by 25%.

Conclusion: Early sun avoidance seems to precede the diagnosis of multiple sclerosis (MS). This protective effect is independent of genetic susceptibility to MS.

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