Associations between circulating ferritin levels and risk of type 2 diabetes mellitus (T2DM) in the included studies. M indicates men and W for women. The data in the EPIC-Norfolk study  were the results of an ad hoc analysis by the original authors, which used quintiles of ferritin levels as exposure and separately reported for men and women. M, men; W, women.
Bao et al. BMC Medicine 2012 10:119 doi:10.1186/1741-7015-10-119