GDF15 and major depressive disorder: There are significant positive associations between higher GDF15 concentrations and both-cognitive-frailty-and-depression in all adults (adjusted β = 0.177 [0.044 – 0.310], p = 0.009) and in older adults (adjusted β = 0.238 [0.086 – 0.390], p = 0.002) (both Table 2, model 1).