The ‘U'-shaped relationship that we identified between IGF-1 and depression symptoms is supported by observations of increased reports of lifetime affective disorders in individuals with lower (pituitary dwarfism) and higher (acromegaly) levels of this growth hormone.52, 53, 54 It may be that this apparent differential result for men and women in these existing studies is due to statistical instability. This evidence concerns the gene GH1 and depressive disorder.