IGF1 and depressive disorder: Even though CRP is a biomarker associated with depression (which we have already discussed as one psychological pathway linking loneliness with CVD) [52], the relationship between CRP and loneliness has also not been shown by other studies, including a study that found no evidence that CRP acts as a mediator between loneliness and depression [53], and another study finding that loneliness was associated with higher inflammatory markers such as insulin-like growth factor 1 (IGF-1) but not CRP or fibrinogen, even though social isolation was related to these factors [54].