Furthermore, exposure to low water temperatures (0–2 °C) for brief periods, three times a week for three winter months, resulted in reduced levels of adrenocorticotropic hormone (ACTH) and cortisol in the blood [44], and increased catecholamine concentration, which is potentially beneficial for treating depression, as it activates the sympathetic nervous system and raises norepinephrine and β-endorphin levels [41,45]. This evidence concerns the gene POMC and major depressive disorder.