Researchers and psychologists have found that this type of depression often results from unconscious negative thinking and therefore nutritional healing can help in a big way. A variation of dysthymia is double depression which a person with chronic, low-grade depression periodically experiences major depressive episodes, then returns to their normal, mildly depressive state. Some people become more depressive in the winter months when the days are shorter for their eating habits are affected.

source: http://www.vitalnutritionals.com/nutritional-healing/curing-depression-through-nutritional-healing/