Does Cigarette Smoking Protect the Appearance of Parkinson’s Disease?

Abstract & Commentary

Source: Hernan MA, et al. Cigarette smoking and the incidence of Parkinson’s disease in two prospective studies. Ann Neurol. 2001;50:780-786.

Persons in their late 60s who smoke heavily or even lightly may be susceptible to several illnesses, especially cancer and cerebral-cardiopulmonary illnesses. Remarkably, however, individuals who smoke cigarettes appear to suffer less risk of developing Parkinson’s disease (PD) than those who never smoked. Up until 20 years ago, women may have been less scrupulously evaluated neurologically for PD, thereby quietly overlooked it as just increasing aging. To determine the accuracy of their past and future health or illnesses, 121,700 cooperating nurses were incorporated in 1976 to a 20-year Nurses Health Study (NHS). Each member on admission submitted an immediate thorough, beginning medical profile, after which she biennially commented her own health and habits as well as other appropriate public health matters. Ten years after the NHS started, a similar Health Professionals’ Follow-up Study (HPFS) was established in men in 1986. This group included 51,529 cooperating male dentists, optometrists, osteopaths, pharmacists, podiatrists, and veterinarians. All were aged 40-75 years old at the start and provided a male’s immediate health profile as well as 4 more biennial reports until 1996.

In the ultimate 20-year female group, 152 new diagnoses of PD were reported in June 1996. Eighty-six had been "never smokers," whereas 66 had been "ever (random) smokers." During the 10-year 1986-1996 decade of 51,529 HPFS, males identified 128 new diagnoses of PD. The greater incidence of PD was found to be in both genders who had never smoked. In both genders the incidence and severity of PD could be calculated in relation to the degree of smoking. Among males aged 70-74 years per 100,000 the projected PD of a "never smoker" would be 153 per cases. "Ever smokers" of the same age only developed an incidence rate of 71 per 100,000. Calculations among "never" smoking women aged 70-74 years per 100,000 indicated an incidence of 50 of PD, but only an incidence of 31 in an "ever smoker." As Hernan and colleagues put it: ultimate age-adjusted ratios (for women) for PD compared to never-smokers amounted to 0.7 for past smokers and 0.4 for current smokers. Adjusted male rate ratios for PD compared to never-smokers amounted to 0.4 for past smokers and 0.3 for current smokers.

Commentary

Previous prospective studies have identified that men who never smoked have an increased incidence of PD when they pass 60 years of age. This present analysis contained a large number of relatively younger women and compared them with a somewhat older and smaller group of men. The incidence of PD in men was measurably higher than in women, but compared with age and gender, PD was much less in both women and men who smoked than didn’t smoke. No satisfactory explanation explains this relationship. Also, although nonsmoking women also develop more PD than smoking women do, the expression shows the trait only after about age 65 and remains less functionally disabled in female than male PDs. —Fred Plum, MD. Dr. Plum, University Professor, Weill Medical College, and Attending Neurologist, New York Presbyterian Hospital, is Editor of Neurology Alert.