Not getting enough rest, or an extended lack of restful sleep can have a variety of negative impacts on your physical health. Poor sleep habits are a common problem, with nearly 25 percent of U.S. adults reporting that they obtain insufficient sleep at least 15 nights a month, and 11 percent reporting inadequate sleep every night. A lack of sleep can increase stress levels, reduce the body's capacity for normal cellular functioning, and create conditions that may cause or contribute to thinning hair and hair loss in men and women.