The symptoms of Parkinson’s disease are fairly well known—tremors of the limbs or face; slow, stiff movements; and poor coordination. However, the cause of this chronic, degenerative, and life-altering disease remains a mystery. It is known that the symptoms are caused by a lack of dopamine in the brain. This neurotransmitter allows us to control movements. In the brains of people with Parkinson’s, the cells that produce dopamine die off, hindering the ability to control movement and balance. Several epidemiologic studies have found that the more people smoke, the less likely they are to develop Parkinson’s. Similar trends are seen for intake of caffeine and alcohol. Scientists are examining why this link exists.

A group of British researchers tested the theory that higher levels of smoking, caffeine intake, and alcohol use are linked to Parkinson’s because they are expressions of a certain personality type—impulsive sensation seeking or thrill seeking. Their findings, published in the March 2006 of the Journal of Neurology, Neurosurgery, and Psychiatry , showed that people with Parkinson’s disease scored significantly lower on tests of thrill-seeking behavior than people without this disease.

About the Study

Researchers in London recruited 106 patients with Parkinson’s disease and 106 “controls”—people of the same age and sex as the Parkinson’s patients, but without the disease. Each volunteer completed the following questionnaires: the sensation seeking scale (SSS), the Trait Anxiety Inventory (TAI), and the Geriatric Depression Scale (GDS). They also described their experience with smoking (past and present), as well as their intake of alcohol and caffeine over the past month. The researchers compared responses from the two groups.

People with Parkinson’s disease scored higher on depression and anxiety scales and lower on the SSS, meaning they are less likely to be thrill seekers, than the controls. The use of cigarettes, alcohol, and caffeine were also significantly lower among people with Parkinson’s disease. Independent of these three health behaviors, a lack of the thrill-seeking personality was associated with an increase in disease incidence. In combination, this personality trait accounted for some, but not all, of the links between each health behavior and Parkinson’s disease.

In this kind of epidemiologic study, in which researchers collect data after people develop a disease, it is not possible to prove that any trait or habit causes the disease. It can, however, identify interesting associations.

How Does This Affect You?

Do smoking and taking unnecessary risks have some merit after all? Common sense tells us no. Fear of Parkinson’s will never become a legitimate reason to smoke or drink alcohol excessively. These findings are provocative, though, because they add another piece—a predisposing personality trait—to the Parkinson’s puzzle. Dopamine is known to be involved in reward and pleasure-seeking behavior. It’s plausible to suppose that individuals who tend to shy way from risky activities have a lower brain reserve of dopamine, and are, therefore, more likely to eventually develop symptoms of Parkinson’s.

This is not to say that all, or even most, conservative-minded straight-shooters are at increased risk of Parkinson’s. This a complex, degenerative condition that quite likely results from numerous risk factors unrelated to personality. Still, any inkling regarding factors contributing to this mysterious disease is welcome and could eventually lead to new treatments and earlier diagnosis.

Depression and anxiety were also highlighted in this study. Aside from their link to Parkinson’s, each of these conditions can be debilitating and should be treated. It’s important to keep the risk of Parkinson’s in perspective—about 50,000 new cases are diagnosed each year and one million Americans are afflicted. In comparison, depression is also a risk factor for heart disease, which affects 61 million Americans.