It is well known that, during the winter, people living in the Northern Hemisphere tend to experience more depression and listlessness. Sometimes called Seasonal Affective Disorder (SAD), this syndrome may be caused by chemical changes in the brain during extended periods of darkness. In addition, the human body needs at least a few minutes of sunlight a day to generate Vitamin D. Vitamin D deficiency is a chronic problem in many northern states in America, where it can lead to feelings of depression and a lack of energy and even libido.