Dr Jane Green

Clinical Epidemiologist at the University of Oxford  

研究チームが言うように、社会的地位が高いほど脳腫瘍の発症リスクが高くなるという報告は新しいものではありません。本論文は良質な大規模データを対象に、教育、収入、職業的地位などを検討しており、その点はよいと思います。

一方で、著者自身が論文で述べているように、社会的地位によって発症リスクが異なる理由について明らかにできていません。もちろん、収入や教育は疾患リスクに影響を与えていると思いますが、それを裏付ける根拠が得られなかったようです。ただ、著者らは、高収入か否かによって異なる2つの要素（男性の喫煙、女性のホルモン補充療法）に言及しており、興味深いと思いました。

原文

“As the authors say, the fact that higher socioeconomic status has been linked to higher risk of brain tumours is not new. This paper is based on large numbers with good follow-up, and it is good to look at more than one measure – in this case, education, income and occupational status – because they tend to measure different aspects of socioeconomic status, which can be hard to define.

“The results generally confirm the links between higher socioeconomic status and risk of brain tumours. But I would interpret apparent differences between the risks in men and women and for the different tumour types with caution – the way the risks are reported here makes it hard to say which risk differences might be real.

“Even though this was a large study, by the time people had been divided into several income, occupational, and educational groups, the number of cases in some subgroups was small, meaning that the estimates of risk were not very precise (as shown by wide confidence intervals). Nor were risks between men and women, or by type, compared formally with each other [there are statistical tests to do this]: sometimes a risk will be 'significant' in one group and 'non-significant' in another just because the size of the group is different, not because the two risks are different from each other.

“For example, risk related to high university education for meningioma was (RR) 1.12 (95%CI 0.94-1.33) in men – 'non-significant', based on 180 cases – and 1.16 (1.04-1.29) in women ''significant', based on over 500 cases. These two relative risks are probably not 'really' different- in fact they are clearly similar- and it is misleading to report one as associated and the other not, on the basis of their individual statistical significance.

“What this study cannot do (and the authors note this) is look at why there may be differences in risk by socioeconomic group. Of course, no one thinks that income or education themselves directly affect disease risk. This study used disease register information and had no data on individual characteristics or lifestyle factors which might explain the links observed (and do appear to explain similar links seen between socioeconomic status and risk of other diseases, such as some cancers). 

“The authors mention smoking; two additional factors which might be interesting in this context are height and, in women, hormone replacement therapy. Risk of brain tumours (as of most cancers) is higher in taller people, and taller people tend to be richer and more educated. HRT increases risk of brain tumours, and its use tends to vary by socioeconomic group.”