Low cholesterol and Parkinson's disease
Parkinson's disease seems to have similar causes to Alzheimer's disease although it affects only about one-tenth as many people as does Alzheimer's.
The symptoms of Parkinson's disease include muscle rigidity and tremor of the hands, which can become increasingly difficult to control as Parkinson's disease advances, particularly with the development of motor complications, such as end-of-dose wearing off and uncontrollable movement following long-term therapy.
There is much evidence that suggests a link between low levels of cholesterol and Parkinson's disease.
The Rotterdam Study, involving 6,465 people aged over 55 examined over an average follow-up period of 9.4 years showed that this link was there. Higher levels of total cholesterol in the blood were associated with a significantly decreased risk of Parkinson's disease. The highest risk was found with cholesterol levels below 6.1 mmol/L [235 mg/dL].
Using that as a reference, they found that the risk dropped to 58% in the cholesterol range 6.1 and 6.8 [235 and 260]; it dropped to 46% between 6.8 and 7.4 [260 and 285mg/dL]; and with a cholesterol level above 7.4  the risk was down to only 16%. Strangely, however, this link was only seen in women.
1. de Lau LML, Koudstaal PJ, Hofman A, Breteler MMB. Serum Cholesterol Levels and the Risk of Parkinson's Disease. Am J Epidemiol 2006; 164: 998-1002