Parkinson's disease is associated with an increased risk of falls. The risk is greatest in patients with advanced disease. Because Parkinson's disease usually occurs late in life, the risk factors related to the neurological impairments add to those associated with aging. The incidence of fractures is high in patients with Parkinson's disease, with femoral neck fractures in older women being particularly common. Risk factors for fractures include a low body mass index, limited exposure to sunlight, an inadequate vitamin D intake with low 25-OH vitamin D levels, and bone loss. Several studies found decreased bone mineral density values at the femoral neck and lumbar spine in patients with Parkinson's disease. Although this decrease is ascribable in part to factors unrelated with Parkinson's disease, such as older age and female gender, Parkinson's disease itself also plays a role, most notably in patients with severe neurological impairments (Hoehn and Yahr stages III and IV).