Book excerpt: SAD is depression caused by lack of natural light. People who have limited exposure to light, and people who live in northern climates are most likely to suffer from SAD, though many people undergo seasonal variations in mood, energy, appetite and sleep. With SAD, sufferers experience an exaggerated version of these changes. Full-blown SAD can be extremely debilitating; the sufferer finds it difficult to carry out normal activities. The disease is often undiagnosed because the symptoms are general enough that they can be attributed to a variety of causes. SAD can be treated with or without medicine, depending on the severity. The book describes helpful changes to eating patterns and vitamin and mineral supplements, ways of adapting your lifestyle to take advantage of the daylight, as well as lightbox therapies. The book distinguishes SAD from classic depression, chronic fatigue, and other illnesses with similar symptoms. It also explains the alarming physical effects of lack of sunlight, which include a greater risk of heart disease, osteoporosis, and even cancer. Written in an informal style, with helpful tips and advice, this book is important for anyone who ever questioned their feelings on a cloudy day or during the winter months.