The delusion of meta-analysis: fish and depression

"The characteristics of the studies included in this meta-analysis are present in online supplementary file 1. The 26 studies were published between years 2001 and 2014, and involved a total of 150 278 participants. Of these studies, 10 were cohort studies12 ,13 ,16–19 ,26,28 and 16 were cross-sectional studies.11 ,14 ,15 ,27 ,29–32 With regard to the study continent, 10 studies were conducted in Europe,11–15 ,29 ,31 ,32 7 in North America,16 ,17 ,27 ,28 4 in Asia,18,27 ,30 3 in Oceania19 ,26 and 2 in South America.27 Nine studies evaluated the association between fish consumption and depression in men,12 ,15 ,16 ,26 ,28–30 ,32 and 10 studies did so in women.11 ,12 ,15–17 ,19 ,26 ,28 ,30 ,32 One study30 was conducted among adolescents and the rest were conducted among adults. The major adjustment confounding factors included age, gender, marital status, education, smoking, alcohol use and body mass index. Quality assessment showed that the Newcastle-Ottawa score of 14 articles was not less than 7, indicating that the methodological quality was generally good (see online supplementary file 2)"

1/ No RCT.
2/ Very disappointing relative risk reduction

http://jech.bmj.com/content/early/2015/08/21/jech-2015-206278.full