Smoking and Parkinson's disease. Search for a dose-response relationship

High IQ in Early Adulthood Is Associated with Parkinson's Disease

Background:

High education level and high occupational complexity have been implicated as risk factors for Parkinson’s disease (PD).

Objective:

The objective was to determine whether cognitive capacity, measured as IQ, in early adulthood is associated with the subsequent development of PD.

Method:

Data on IQ were retrieved from the Swedish Military Service Conscription Registry, comprising Swedish males who enlisted for military service in the period 1968–1993 (N = 1,319,235). After exclusion, 1,189,134 subjects in total were included in the present study. Individuals who later developed PD (N = 1,724) were identified using the Swedish National Patient Register and the Swedish Cause of Death Register.

Results:

High education level was associated with PD. High IQ was associated with PD (p < 0.0001), both when analyzed as a continuous variable and when divided into three categories. The hazard ratio for the high IQ category compared to the low IQ category was 1.35 (95% confidence interval 1.17–1.55). Strong test results on the subtests, measuring verbal, logic, visuospatial and technical abilities, were also associated with PD. In a subgroup, smoking was inversely associated with PD, as well as with IQ.

Conclusions:

This study identifies high IQ to be a risk factor for PD.

Tobacco Use, Oral Health, and Risk of Parkinson's Disease

Few studies have investigated the associations between use of Swedish moist snuff (snus), associated poor oral health, and risk of Parkinson's disease (PD). We followed 20,175 participants who were free of PD in 1973-1974 in Uppsala, Sweden, until the end of 2012. We used Cox proportional hazards regression models to estimate hazard ratios and corresponding 95% confidence intervals for the associations between tobacco use, oral health indicators, and PD risk. We found that tobacco use was associated with a lower risk of PD in males. Compared with males who never used any tobacco daily, pure ever tobacco smokers, pure ever snus users, and combined users had adjusted hazard ratios of 0.68 (95% confidence interval (CI): 0.49, 0.93; n = 83), 0.51 (95% CI: 0.27, 0.95; n = 11), and 0.21 (95% CI: 0.07, 0.67; n = 3), respectively. No association was observed for number of teeth, dental plaque, or detectable oral mucosal lesions and PD risk, although there was a suggestive association with Candida-related oral mucosal lesions in males (hazard ratio = 1.56, 95% CI: 0.92, 2.65; P = 0.098). Use of snus is associated with a lower risk of PD in males, while poor oral health seems not to be associated with PD occurrence.

Epidemiology and etiology of Parkinson's disease: a review of the evidence

The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.

Smoking and tea consumption delay onset of Parkinson's disease

Cigarette smoking, coffee and tea drinking may protect against Parkinson's disease (PD). These factors were assessed, retrospectively, to measure their effect on the age of PD onset. The study population consisted of 278 consecutive PD patients. Smoking > or =10 pack-years delayed age of PD onset by 3.2 years (p<0.05). Consumption of tea more than 3 cups per day delayed age of motor symptoms onset by 7.7 years (p<0.01). Coffee consumption exceeding 3 cups per day advanced the age of PD onset by 4.8 years (p=0.03). Thus, tea consumption and smoking can delay the age of PD onset, while coffee drinking may have the opposite effect.

The effect of cigarette smoking, tea, and coffee consumption on the progression of Parkinson's disease

Previous epidemiological studies found a negative association between cigarette smoking, tea or coffee drinking with the occurrence of Parkinson's disease (PD). However, it is unknown how these factors affect the rate of progression of the disease. A retrospective study was conducted among 278 consecutive PD patients. Data on smoking and coffee or tea consumption were obtained through direct or proxy interviews, and the time from onset of motor symptoms until reaching Hoehn & Yahr (H&Y) stage 3 was retrieved from the case records. Cox proportional hazards model and Kaplan-Meyer model were used to estimate whether the dependent variables (smoking, drinking coffee or tea) affect the rate of progression of the disease, which was measured by the time it took patients to reach H&Y stage 3. We found that disease progression was not affected by cigarette smoking, tea or coffee consumption. The present study suggests that these variables do not have a disease modifying effect in already diagnosed PD patients.

A case-control study of Parkinson's disease in urban population of southern Israel

BACKGROUND

In recent years, an increased prevalence of Parkinson's disease (PD) in southern Israel was observed. The aim of this study was to determine which exposures are associated with PD in the urban population of this region.

METHODS

Ninety-three PD patients living in towns were compared to 93 age and sex matched controls. A previously validated questionnaire, including demographic data, education, data on exposures, previous diseases, family history and habits, was administered.

RESULTS

In multivariate logistic regression analysis, it was found that history of work in construction sites was the strongest predictor of PD risk, followed by exposure to pesticides. In contrast, there was a negative association with smoking and history of mechanical factory employment. When the same statistical analysis was limited to association of PD with smoking, pesticides and construction work, the latter was found to be the strongest risk factor.

CONCLUSION

The risk factors for PD in this population are work on a construction site and exposure to pesticides.

Genetic and environmental risk factors in Parkinson's disease

Parkinson's disease (PD) is a multifactorial disorder, caused by a combination of age, genetics and environmental factors. Nigral cells are susceptible to multiple causes of derangement of normal cell function, all of which may contribute to the same Parkinson phenotype. Autosomal dominant alpha-synuclein-gene PD represents one of the pure genetic forms, whereas cases of sporadic PD probably depend more on age and environmental factors, MPTP-Parkinsonism being the purest example of an environmentally caused Parkinson phenotype. This review suggests that pesticides-herbicides, smoking and head trauma probably represent the most eligible candidates for environmental factors involved in provoking PD or influencing its natural course.

Genetic association between cytochrome P450IA1 gene and susceptibility to Parkinson's disease

Idiopathic Parkinson's disease (PD) is a multifactorial neuro-degenerative disorder resulting from environmental factors acting on genetically susceptible individuals with normal aging. Cytochrome P450IA1 is a dioxin-inducible enzyme which is responsible for the activation of procarcinogens and environmental pollutants, such as benzo[alpha]pyrene and other aromatic hydrocarbons. The frequencies of polymorphic alleles of cytochrome P450IA1 gene (CYPIA1) were studied in 126 unrelated patients with PD in comparison with 176 healthy Japanese. The frequency of the Msp I polymorphic allele, a variant of CYPIA1 (m2), was significantly higher in patients with PD (0.444) than in controls (0.349). The risk of PD in homozygotes for m2 was 2.34-fold greater than homozygotes for the wild-type, m1. The relative risk for PD in homozygotes for CYPIA1Val was 6.54-fold higher than in homozygotes for the wild type (CYPIA1Ile)(p < 0.001). These results strongly suggest that the CYPIA1 might be one of the susceptibility genes for PD.

The "protective" influence of cigarette smoking on Alzheimer's and Parkinson's diseases. Quagmire or opportunity for neuroepidemiology?

The negative association between smoking and both Alzheimer's (AD) and Parkinson's (PD) diseases is a consistent epidemiologic finding. This observation has prompted many investigators to conclude that cigarette smoking must be "biologically protective" against AD and PD. Rather than suggesting some as-yet-undefined pathogenetic clue, however, this negative association more likely is indicative of the under-appreciated influence of differential survival in epidemiologic studies.

Genetic and environmental aspects of the role of nicotinic receptors in neurodegenerative disorders: emphasis on Alzheimer's disease and Parkinson's disease

As neurodegenerative disorders are better characterized, the importance of genetic and environmental interactions is becoming more evident. Among the neurodegenerative disorders, Alzheimer's disease and Parkinson's disease are both characterized by large losses of nicotinic binding sites in brain. In addition, losses in nicotinic receptors occur during normal aging. Chronic administration of nicotine in man or experimental animals increases the number of nicotinic receptors in brain. Nicotine has been shown to possess some neuroprotective properties for both cholinergic and dopaminergic neurons. These neuroprotective properties, when better understood, may provide important information on normal aging and neurodegenerative disorder related neuronal cell death. Understanding the functional aspects of neuronal nicotinic receptor subtypes may lead to successful therapeutic treatments or disease preventative strategies for neurodegenerative disorders.

Could seborrhoeic dermatitis be implicated in the pathogenesis of parkinsonism?

The spouses of a group of aged sufferers have been demonstrated to have multifarious differences relevant to parkinsonism from matched controls, which were difficult to explain by selective mating, learned or reactive behaviour. Could parkinsonism be transmissible? The frequency of inflammation and scaling on head or neck was greater (P = 0.05) in these spouses (19 available) than in controls (36), the best discriminating site of inflammation being scalp (P = 0.02). Both seborrhoeic dermatitis and overt, or pre-clinical, parkinsonism occurred in sufferers and spouses: to presume they are not causally related is to accept multiple entities. In favour of seborrhoeic dermatitis being causal for parkinsonism, rather than vice versa, is the involvement of a known organism, Pityrosporum ovale, in the dermatitis, and that the evidence of parkinsonism in the spouses indicated that they were only part way down the path towards the clinical condition.

Risk-factors for Parkinson's disease: case-control study in the province of Cáceres, Spain

This case-control study, performed in a mixed rural and urban province, of 74 patients with Parkinson's disease (PD) and 148 unselected age and sex-matched controls, attempted to look possible risk factors for PD. Rural living, well-water drinking, positive family history for PD and postural tremor, were associated to an increased risk for PD, with results regarding exposure to pesticides near to statistical significance. Alcohol-drinking habit in males were associated to a decreased risk for PD, with results regarding cigarette-smoking habit in males near to statistical significance. We did not find association between the risk for PD and the following variables: 1) exposure to industrial toxins; 2) agricultural work; 3) cranial trauma; 4) previous common illnesses including some infections, arterial hypertension, diabetes mellitus, coronary heart disease and thyroid disease; 5) coffee and tea drinking habits.

The genetics of Parkinson's disease

The possibility of a major contribution of hereditary factors to the cause of Parkinson's disease (PD) is being reconsidered by many. The studies preceding the 1980s presented conflicting evidence and suffered from procedural difficulties. The emergence of the MPTP hypothesis and the failure of three twin studies to document a strong hereditary component in the early 1980s turned attention toward an environmental cause of PD. However more recent descriptions of deficiencies in genetically-coded biochemical functions in PD, more sophisticated clinical family analyses, re-analysis and extension of the twin studies and the emergence of several large autopsy-proven PD kindreds raise the possibility of an important heritable factor in PD.

Premorbid smoking, alcohol consumption, and coffee drinking habits in Parkinson's disease: a case-control study

A number of studies have reported lower cigarette consumption in patients with Parkinson's disease (PD) previous to onset of the disease. In an attempt to determine whether there existed a "premorbid attitude" by patients against the use of socially accepted "drugs," the premorbid tobacco, alcohol, and coffee consumption habits were compared in 128 PD patients and 256 controls. Patients and controls were selected by case control method and were recruited from the same health area and socioeconomic stratum. In males, the habits of smoking more than 10 cigarettes/day (p < 0.001) and drinking more than 50 g/day of alcohol (p < 0.001) were significantly less frequent in the PD patients than in the controls, but the differences in coffee consumption were nonsignificant. In females behavior did not differ significantly between the PD group and the controls for any of the three habits. There was no correlation between the amount of smoking and alcohol drinking and age at onset of PD or current Hoehn and Yahr's staging. Our results suggest the existence of a premorbid personality in males with PD, possibly conditioning a restrictive attitude toward the consumption of such toxic substances as tobacco and alcohol, yet a more tolerant attitude toward habits more widely accepted socially, like coffee consumption.

Epidemiology of Parkinson's disease

Additional epidemiologic studies may provide important insights into the etiology of Parkinson's disease. Moreover as the elderly population of Europe and the United States grows, accurate public health planning requires accurate incidence and prevalence estimates. The recent development of a therapy that may slow disease progression (see article by Tetrud elsewhere in this issue) makes early identification and treatment of Parkinson's disease particularly important. Investigations of early markers of Parkinson's disease or markers of disease susceptibility are critical areas of future research, requiring careful collaboration between epidemiologists and laboratory scientists.

Smoking and movement disorders in psychiatric patients

Previous studies have suggested that tardive dyskinesia may occur more frequently in patients who smoke. Further evidence of an interaction between smoking and movement disorders includes the low lifetime exposure to cigarettes found in Parkinson's disease patients. In this study 126 patients with chronic psychiatric illnesses were blindly evaluated for tardive dyskinesia, neuroleptic-induced parkinsonism, and akathisia. Patients who smoked received significantly higher doses of neuroleptics but did not have significantly more frequent or more severe tardive dyskinesia or parkinsonism. Female smokers did have significantly more akathisia. These results are discussed with regard to interactions between smoking, central dopaminergic tone, and the psychopathology of extrapyramidal syndromes. The effect of smoking on neuroleptic blood levels as well as clinical symptomatology is also discussed.

Epidemiological approaches to the etiology of Parkinson's disease

In the search for the cause of Parkinson's disease epidemiology serves several purposes. Valuable clues to the etiology may be derived from the epidemiological features of the disease, and the subsequent search for risk factors in analytical studies can be narrowed correspondingly. On the other hand, knowledge of the epidemiology of Parkinson's disease is necessary in creating etiological hypotheses, since only hypotheses consistent with the epidemiological profile deserve careful testing.

Hypothesis: a nicotine-dopamine interaction linking smoking with Parkinson's disease and tardive dyskinesia

1. Nicotine, an important pharmacological component of cigarette smoke, is known to have significant effects on central nervous system (CNS) dopaminergic function. Although acute doses of nicotine have been shown to facilitate dopamine release, recent data indicate that chronic nicotine treatment may actually decrease CNS dopamine turnover in the striatum. 2. A number of epidemiological investigations have demonstrated that individuals who are or who have been smokers are less likely to develop idiopathic Parkinson's disease (a disorder involving a deficit in nigrostriatal dopaminergic neurotransmission). In addition, there is preliminary evidence that individuals with tardive dyskinesia (a hyperkinetic movement disorder observed in some cases of chronic neuroleptic treatment and thought by some to be associated with striatal dopamine receptor supersensitivity) are more likely to be smokers. 3. A unitary hypothesis is presented, proposing that smoking in early adult life may decrease CNS catecholamine turnover, thereby protecting against free radical formation from catecholamine oxidation that in turn damages striatal neurons. These individuals are thereby "protected" from the later development of Parkinson's disease. In this hypothetical scheme, individuals who are given neuroleptics and who also are smokers may develop a greater degree of dopamine receptor supersensitivity due to combined receptor blockade by neuroleptics and a decrease in CNS dopamine turnover caused by nicotine, resulting in an increased prevalence of tardive dyskinesia in this group.

The relevance of the Lewy body to the pathogenesis of idiopathic Parkinson's disease

The Lewy body is a distinctive neuronal inclusion that is always found in the substantia nigra and other specific brain regions in Parkinson's disease. It is mainly composed of structurally altered neurofilament, and occurs wherever there is excessive loss of neurons. It occurs in some elderly individuals and rarely in other degenerative diseases of the central nervous system. In 273 brains of patients dying from disorders other than Parkinson's disease, the age-specific prevalence of Lewy bodies increased from 3.8% to 12.8% between the sixth and ninth decades. Associated pathological findings suggest that these cases of incidental Lewy body disease are presymptomatic cases of Parkinson's disease, and confirm the importance of age (time) in the evolution of the disease. In view of the common and widespread occurrence of this disorder we propose that endogenous mechanisms operating in early life may be more important than environmental agents in the pathogenesis of Lewy bodies and Parkinson's disease.

Validity of a mailed epidemiological questionnaire and physical self-assessment in Parkinson's disease

The large-scale mail questionnaire is a useful tool in epidemiological investigation and will probably come into wider use in the search for an environmental cause of Parkinson's disease (PD). To determine the validity of mail questionnaires in patients with PD, we administered a 17-item questionnaire by in-person interview, as a standard, to 68 patients (and/or a relative when necessary) and compared the results with the same questionnaire mailed at least 1 month before or after the interview. Questions in three formats requested recall of the clinical course and past environmental factors. Each patient also completed a multiple-choice physical self-assessment (a modification of four items on the Columbia Scale) immediately before seeing the neurologist, who completed the same form after the examination. Percent of patients with zero discordance between mail and interview responses averaged 52% for the nine fill-in-a-year items, 53% for the three list-generation items. Kappa statistics for the five multiple-choice items, which each offered four choices, averaged 0.67 (range 0.40-0.89). Kappa for the physical examination items, each rated on a 0-3 scale, was finger-tap 0.12, gait 0.34, tremor 0.35, and chorea 0.20. Patients' ratings tended to be more severe than neurologists' ratings. We conclude that mail surveys in PD should either be avoided or rigorously pretested for validity.

Environmental factors in the etiology of Parkinson's disease

Parkinson's disease (PD) has been proposed to result from the interaction of aging and environment in susceptible individuals. Defective metabolism of debrisoquine, inherited as an autosomal recessive, has been associated with this susceptibility. In 35 PD patients and 19 age-matched controls, no significant differences in debrisoquine metabolism were found, although a trend to impaired metabolism was noted in patients with disease onset less than or equal to 40. Foci of PD patients were associated with rural living and well water drinking, or rural living coupled with market gardening or wood pulp mills. In a questionnaire survey, patients with PD onset less than or equal to age 47 were significantly more likely to have lived in rural areas and to have drunk well water than those with onset greater than or equal to age 54 (p less than or equal to 0.01). Because of population mobility in North America, a case-control study designed to test environmental, occupational, dietary and other proposed risk factors for PD was conducted in China, where the population is more stationary and the environment more stable. No significant differences in incidences of head trauma, smoking or childhood measles were found between patients and controls.

Geography, drinking water chemistry, pesticides and herbicides and the etiology of Parkinson's disease

In 1984 we made the first observation of a correlation between early age exposure to rural environment (and drinking well water) and development of idiopathic Parkinson's disease (IPD). These findings were subsequently confirmed elsewhere (Barbeau, 1985;25 Tanner, 1985). Analysis of all early age onset IPD (EPD) cases born and raised in Saskatchewan revealed that 20 of 22 had exclusively rural exposure during the first 15 years of life. This distribution was significantly different from the general population (p = 0.0141). Further study of the EPD group included sampling and metal analysis of childhood sources of drinking water in 18 cases and 36 age and sex-matched controls. Water collected from the two groups was analyzed for 23 metals (including 7 elements implicated in the etiology of IPD). There was no difference in the metal composition of the water between the two groups. Finally, a review of herbicide and pesticide use in Saskatchewan agriculture was undertaken to determine if there was an increased incidence of EPD following utilization of any particular chemical. No increase was found in the incidence of EPD with the introduction of any pesticide or herbicide, including Paraquat, for agricultural use. We conclude that there is a strong correlation between early age rural environmental exposure and development of IPD. We believe well water is a likely vehicle for the causal agent, but neither water metal concentration nor any of the herbicides and pesticides used in Saskatchewan agriculture are related to the cause.

Exposure to cigarette smoke does not decrease the neurotoxicity of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice

Epidemiological surveys have repeatedly shown that idiopathic Parkinson's disease (PD) occurs less frequently in persons who have smoked cigarettes for many years than among age-matched non-smokers. Since PD might be caused by neurotoxins chemically similar to N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), we explored the possible protective effect of repeated exposure to cigarette smoke against MPTP neurotoxicity in the C57 black mouse. Mice given MPTP and exposed to cigarette smoke suffered just as great a depletion of striatal dopamine as did mice treated only with MPTP. We discovered also that different lots of C57 black mice obtained from a single supplier can have markedly different sensitivities to MPTP.