That's what the authors say: > Despite having adjusted for several potential confounders, the major shortcoming of this study is the inability to distinguish b

That's what the authors say: > Despite having adjusted for several potential confounders, the major shortcoming of this study is the inability to distinguish between the consequences of an unhealthy lifestyle and of avoidance of sun exposure. Take depression for example. None of the factors you mentioned would control for it and depression is often not diagnosed, especially early on.