The Effects of Vitamin D and Bone Loss in Parkinson's Disease

Health care burdens from neurodegenerative diseases are expected to increase disproportionately. Increasing age also predisposes this same population to other chronic diseases including osteoporosis, a progressive systemic skeletal disease characterized by low bone mass, which leads to an increase susceptibility to fractures. In the United States, 44 million people are estimated to be at risk for osteoporosis and low bone mass emphasizing the enormity of this public health problem. Parkinson's disease is a progressive neurodegenerative disorder affecting about 1 million people. Evidence indicates that Parkinson's disease patients are at a higher risk for low bone mineral density, which can contribute to increased fractures compared to healthy subjects. In fact, several risk factors of osteoporosis in patients with PD have been identified, including advanced stages of PD, low body mass index, inadequate sunlight exposure and decreased vitamin D levels. Some or all of these factors in conjunction with decreased immobilization that may occur with PD, put patients at increased risks for fractures. Few studies however have examined bone markers in PD patients. Even fewer studies have examined the impact of Vitamin D supplementation on bone metabolism and mineralization in PD patients. Vitamin D is an essential component in bone health, promoting calcium absorption in the gut and maintaining adequate serum calcium and phosphate concentrations, which enable normal mineralization of bone.

Parkinson's disease is the second most common neurodegenerative disorder after Alzheimer's disease affecting approximately 1% of the population older than 50 years. There is a worldwide increase in disease prevalence due to the increasing age of human populations. The disease is characterized by tremor, stiffness of the limbs and trunk, impaired balance and coordination, and slowing of movements, leading to immobility and frequent falls. Patients also sometimes develop other symptoms, including difficulty swallowing, disturbed sleep, and emotional problems. Parkinson's disease results from the loss of dopaminergic neurons in the substantia nigra region of the brain. The cause and mechanism of continued neuron cell death in the substantia nigra is currently unknown. Epidemiological studies suggest an association between Parkinson's disease and osteoporosis, vitamin D inadequacy and altered bone and mineral metabolism. Accumulating evidence indicates that patients with Parkinson's disease are at a higher risk for fractures compared to healthy subjects. This could be attributed to several contributing factors including increased rate of falls, vitamin D deficiency, reduced body mass index and reduced bone mineral density.