COMT: Catechol-O-methyltransferase; HUNT: "Helseundersøkelsen i Nord-Trøndelag" (The Nord-Trøndelag Health Study); Val: Valine; Met: Methionine; HADS: Hospital Anxiety and Depression Scale; HADS-A: Anxiety subscale of Hospital Anxiety and Depression Scale; HADS-D: Depression subscale of Hospital Anxiety and Depression Scale.