Parkinson’s disease is a disorder of the nervous system that results in loss of muscle control and sometimes dementia. Scientists believe that dementia in Parkinson’s disease occurs as a result of a defect in how the brain metabolizes glucose, or blood sugar. Chronically high blood sugar levels may also be involved in the onset of Parkinson’s disease.
Parkinson's Disease
Parkinson’s disease results from a breakdown of brain cells that produce the neurotransmitter dopamine. No one knows why dopamine-containing neurons begin to break down, though in some individuals it appears to be genetically determined. As dopamine is crucial to motor function, the main symptoms of Parkinson’s disease are related to muscle dysfunction. In early stages, the disease gives rise to tremors, muscle stiffness, slow movements and difficulties maintaining a good posture. In later stages, the motor defects worsen and dementia may occur.
Chronically High Blood Sugar
According to a study published in the April 2007 issue of “Diabetes Care,” there is a higher prevalence of Parkinson’s Disease among individuals with Type 2 diabetes. Type 2 diabetes occurs when insulin receptors on the cell surfaces shut down. Early stages of this phenomenon are also known as insulin resistance and glucose intolerance. When the body’s insulin receptors are impaired, insulin cannot communicate to the cells when glucose is available in the bloodstream. This results in an accumulation of glucose in the blood.
Possible Mechanisms
How high blood glucose levels lead to Parkinson’s disease is unclear. An animal study published in the March 2004 issue of “Lancet Neurology” suggests that irregularities in the function of insulin may play a role in the development of Parkinson’s disease. Brain cells contain binding sites for insulin. One of the roles of insulin in the brain is to regulate dopamine secretion. When the brain’s insulin receptors become defective, insulin cannot regulate the dopamine system. This inhibits the secretion of dopamine. Over time, decreased dopamine secretion could perhaps lead to a disintegration of dopamine-producing neurons.
Dementia
According to a study published in December 1992 issue of “Archives of Neurology,” high blood glucose levels may be involved in the onset of dementia in the later stages of Parkinson’s disease. When insulin cannot signal to the body’s cells that glucose is available as a source of energy, the cells need a different kind of fuel. Most cells in the body can metabolize fat and protein. The brain, however, cannot use fat or protein as a source of energy. When glucose metabolism decreases, the neurons can use ketone bodies, a byproduct from fat metabolism, as a fuel. However, if the body switches to burning protein, the levels of ketone bodies go down and the cells in the brain are starving. This could lead to dementia.
References
- National Institute of Neurological Disorders and Stroke: Parkinson's Disease
- "Diabetes Care"; Type 2 Diabetes and the Risk of Parkinson's Disease; G. Hu, et al.; April 2007
- "Lancet Neurology"; Insulin and Neurodegenerative Disease: Shared and Specific Mechanisms; S. Craft, et al.; March 2004
- "Archives of Neurology"; Cerebral Glucose Metabolism in Parkinson's Disease With and Without Dementia; R.F. Peppard, et al.; December 1992
