Social and occupational differences in chronic obstructive lung disease in Denmark 1981-1993

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is a common crippling disorder related to exposure to noxious dust and fumes. The purpose of this study was to estimate relative rates of COPD in socioeconomic groups and in 'classic' high-risk industries. METHODS: Cohorts of all gainfully employed 20-59 year old Danes in the years 1981, 1986, and 1991 were formed, to compare standardized hospitalization ratios (SHR) and time trends (1981-93). RESULTS: The risk ratio (RR) between unskilled workers and senior salaried staff was 2.31, (95% CI 2.13-2.51) for men and 1.62 (1.38-1.92) for women. Among classic high-risk occupations we found a decreasing SHR in farmers and an increasing SHR in the hotel and restaurant industry and for taxi and bus drivers. The study confirmed earlier reports on high risks in the metal, rubber, and bakery industries. CONCLUSIONS: Apart from the reduced SHR among farmers there were no signs of decreasing differences in COPD risk.     

Hospitalizations among teachers in Denmark, 1981-1997

It is a common notion that teachers constitute a group at high risk of occupational stress, but the potential health consequences of the assumed high stress levels are still poorly illuminated. The aim of the present study was to investigate morbidity among Danish teachers. Cohorts of Danish teachers of primary, secondary and vocational schools, aged 20-59 years in 1981, 1986, 1991 and 1994, were formed to calculate age standardized hospitalization ratios (SHRs) and time trends (1981-1997) for a large variety of diagostic aggregations. Statistically significantly low SHRs for the major disease categories: neoplasms, diseases of the nervous, circulatory, respiratory. digestive and musculoskeletal systems were found both for men and women. We also found significantly low SHRs for the aggregated diagnostic group "injury and poisoning" in men and for diseases of the nervous system and sense organs in women. Age standardized hospitalization rates with respect to diseases observed in practically all systems and organs of the body were statistically significantly lower among teachers compared with other economically active people of Denmark.     

Increasing inequality in ischaemic heart disease morbidity among employed men in Denmark 1981-1993: the need for a new preventive policy.

BACKGROUND: In the mid 1980s European governments committed themselves to the WHO goal 'reduced inequality in health by year 2000' according to which inequality in health should be reduced by 25% by the year 2000. The study aim is to estimate the time trend in relative risk due to ischaemic heart disease (IHD) morbidity in employment status groups in Denmark in the period from 1981 to 1993 and to recommend a strategy to reduce inequality in health. MATERIAL AND METHODS: The study dealt with change in relative risk of IHD in main employment status AND groups as measured in three successive cohorts. The cohorts were defined as all METHODS: gainfully employed men in Denmark as of 1 January 1981, 1986 and 1991, respectively. Information on employment was retrieved for the three previous years. The cohorts were followed for first admissions with IHD as the principal cause during 5, 5, and 3 years respectively. RESULTS: Managers and white collar workers had an average or low and decreasing relative risk while male blue collar workers had a high and increasing relative risk. Thus the social inequality in IHD is rapidly increasing. Some occupational groups are known to be at high risk. Some of these high-risk groups, such as bus drivers, even have an increasing relative risk. CONCLUSIONS: The general health education has been successful in the prevention of IHD in the high-status groups but has failed to reduce the risk among blue collar workers. Preventive measures against IHD should focus on occupational groups at high, increasing risk and the measures should tailor to their 'subculture.'     

A prospective study of night shift work, sleep duration, and risk of Parkinson's disease

The authors prospectively investigated whether working rotating night shifts was associated with the risk of Parkinson's disease among 84,794 female nurses who reported years of night shift work in 1988 (the US Nurses' Health Study). After 975,912 person-years of follow-up (1988-2000), 181 incident Parkinson's disease cases were documented. Compared with nurses who never worked rotating night shifts, those with 15 years or more of night shift work had a 50% lower risk of Parkinson's disease after adjustment for age and smoking (95% confidence interval: 0.26, 0.97; p(trend) = 0.01). Sleep duration was positively associated with Parkinson's disease risk: The relative risk was 1.84 (95% confidence interval: 0.99, 3.42) when comparing nurses who reported 9 or more hours of sleep per day with those who slept 6 hours or less (p(trend) = 0.005). These data suggest that working night shifts may be protective against Parkinson's disease or that low tolerance for night shift work is an early marker of Parkinson's disease. Conversely, habitual longer sleep duration may be an earlier marker of Parkinson's disease. Because of the novelty and the exploratory nature of these findings, confirmation is needed.     

Depression and cancer risk: a register-based study of patients hospitalized with affective disorders,Denmark, 1969-1993

The authors investigated the cancer risk of patients hospitalized for depression in a nationwide Danish cohort study. All 89,491 adults in Denmark who had been admitted to a hospital with depression, as defined in the International Classification of Diseases, Eighth Revision, between 1969 and 1993 were identified. There were 1,117,006 person-years of follow-up. Incidence rates of all cancers and of site-specific cancers were compared with national incidence rates for first primary cancers, with data being adjusted for sex, age, and calendar time. A total of 9,922 cases of cancer were diagnosed in the cohort, with 9,434.6 having been expected; this yielded a standardized incidence ratio of 1.05 (95% confidence interval (CI): 1.03, 1.07). The risk of cancer was increased for the first year after hospital admission, with brain cancer especially occurring more frequently than expected. When the first year of follow-up was excluded, the increase was attributable mainly to an increased risk of tobacco-related cancers: Standardized incidence ratios for non-tobacco-related cancers were 1.00 (95% CI: 0.97, 1.03) after 1-9 years of follow-up and 0.99 (95% CI: 0.95, 1.02) after 10 or more years of follow-up. These data provide no support for the hypothesis that depression independently increases risk of cancer, but they emphasize the deleterious effect that depression can have on lifestyle factors.     

Diet, urate, and Parkinson's disease risk in men

The authors examined whether a diet that increases plasma urate level is also related to reduced risk of Parkinson's disease (PD). The study population comprised 47,406 men in the Health Professionals Follow-up Study. The potential effect of diet on plasma urate level was estimated by regressing plasma urate on intakes of selected foods and nutrients in a subsample of 1,387 men. Coefficients of this regression model were then used to calculate a dietary urate index for all cohort participants. Multivariate relative risks of PD were estimated by means of Cox proportional hazards models. After 14 years of follow-up (1986-2000), the authors documented 248 incident cases of PD. A higher dietary urate index was associated with a lower risk of PD (top quintile vs. bottom: relative risk = 0.47, p-trend = 0.0008), after adjustment for age, smoking, caffeine intake, and other potential confounders. This association remained strong and significant after further adjustment for each component of the index individually (p-trend < 0.02 for each). These data support urate as a potentially protective factor in PD and suggest that dietary changes expected to increase plasma urate level may contribute to lower risk of PD. These potential benefits, however, should be weighed against expected adverse effects on risk of gout and other chronic diseases.     

Obesity and the risk of Parkinson's disease

Dopamine is involved in the regulation of food intake, and obese persons have decreased dopamine D2 receptor availability in the striatum. Furthermore, midlife triceps skinfold thickness has been found to be positively associated with the risk of Parkinson's disease (PD) among Japanese-American men in Hawaii. The authors prospectively investigated whether obesity was associated with PD risk in two large cohorts of US men and women. They documented 249 cases of PD in men (1986-2000) and 202 cases in women (1976-1998). Neither baseline body mass index (weight (kg)/height (m)(2)) nor early adult body mass index was associated with PD risk. The multivariate relative risk for a baseline body mass index of > or = 30 versus <23 was 0.8 (95% confidence interval (CI): 0.6, 1.2; p for trend = 0.3). Overall, waist circumference and waist-to-hip ratio were not related to PD risk. However, among never smokers, both variables showed significantly positive associations with PD risk. The relative risks for comparisons of extreme quintiles were 1.9 (95% CI: 1.0, 3.4; p for trend = 0.03) for waist circumference and 2.0 (95% CI: 1.1, 3.6; p for trend = 0.03) for waist-to-hip ratio. The results do not support a role of overall obesity in PD pathogenesis; however, central obesity may be associated with higher PD risk among never smokers, and this finding merits further investigation.     

Occupational risk factors in Parkinson's disease

BACKGROUND: An apparent excess of teachers and healthcare workers among the Parkinson's disease patients of a large tertiary care movement disorders clinic suggested the hypothesis that high exposure to viral (or other) respiratory infections in these occupations might be a risk factor for Parkinson's disease. METHODS: A case-control study of the association between occupation and Parkinson's disease was conducted. Cases (414) were all Parkinson's disease patients seen at the University of British Columbia Hospital Movement Disorders Clinic between 1986 and 1993, residing in Greater Vancouver, and under 65 in 1991. Controls (6,659) were randomly selected from the 1991 Canadian Census. FINDINGS: Parkinson's disease was associated with teaching (OR 2.50, 95% CI 1.67-3.74) and occupation in healthcare services (OR 2.07, 95% CI 1.34-3.20), but there were several other substantial associations, both positive and negative. INTERPRETATION: While referral bias cannot be ruled out, the authors find the consistency of the overall pattern of associations with the respiratory infection hypothesis striking.     

Erectile function and risk of Parkinson's disease

Erectile dysfunction is common among individuals with Parkinson's disease, but it is unknown whether it precedes the onset of the classic features of Parkinson's disease. To address this question, the authors examined whether erectile dysfunction was associated with Parkinson's disease risk in the Health Professionals Follow-up Study. Analyses included 32,616 men free of Parkinson's disease at baseline in 1986 who in 2000 completed a retrospective questionnaire with questions on erectile dysfunction in different time periods. Relative risks were computed using Cox proportional hazards models adjusting for age, smoking, caffeine intake, history of diabetes, and other covariates. Among men who reported their erectile function before 1986, 200 were diagnosed with Parkinson's disease during 1986-2002. Men with erectile dysfunction before 1986 were 3.8 times more likely to develop Parkinson's disease during the follow-up than were those with very good erectile function (relative risk = 3.8, 95% confidence interval: 2.4, 6.0; p < 0.0001). Multivariate-adjusted relative risks of Parkinson's disease were 2.7, 3.7, and 4.0 (95% confidence interval: 1.4, 11.1; p = 0.008) for participants with first onset of erectile dysfunction (before 1986) at 60 or more, 50-59, and less than 50 years of age, respectively, relative to those without erectile dysfunction. In conclusion, in this retrospective analysis in a large cohort of men, the authors observed that erectile dysfunction was associated with a higher risk of developing Parkinson's disease.     

Folate intake and risk of Parkinson's disease

In clinical studies, individuals with Parkinson's disease have had higher concentrations of plasma homocysteine than did controls, and experimental evidence suggests that folate deficiency or focal administration of homocysteine sensitizes dopaminergic neurons to the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The authors thus prospectively investigated whether higher intake of folate, vitamin B(6), or vitamin B(12) was related to a lower risk of Parkinson's disease in the Health Professionals Follow-up Study (1986-2000) and the Nurses' Health Study (1980-1998). They documented Parkinson's disease diagnoses in 248 men and 167 women during the follow-up. Folate intake was not associated with the risk of Parkinson's disease; the relative risks for the highest compared with the lowest quintiles were 1.0 (95% confidence interval: 0.7, 1.5) in men and 1.3 (95% confidence interval: 0.8, 2.3) in women. Neither did they find significant associations in analyses stratified by age, smoking, alcohol consumption, or lactose intake. Intake of vitamin B(6) or vitamin B(12) also was not related to the risk of Parkinson's disease. The current study does not support the hypothesis that higher intake of folate or related B vitamins lowers the risk of Parkinson's disease.     

Plasma urate and risk of Parkinson's disease

Oxidative stress contributes to dopaminergic neuron degeneration in Parkinson's disease. Urate, a potent antioxidant, could be neuroprotective. To determine whether higher plasma concentrations of urate predict a reduced risk of Parkinson's disease, the authors conducted a nested case-control study among participants in the Health Professionals Follow-up Study, a cohort comprising over 18,000 men who provided blood samples in 1993-1995. Eighty-four incident cases of Parkinson's disease were diagnosed through 2000, and each was randomly matched to two controls by year of birth, race, and time of blood collection. Rate ratios of Parkinson's disease according to quartile of uricemia were estimated by use of conditional logistic regression. The mean urate concentration was 5.7 mg/dl among cases and 6.1 mg/dl among controls (p = 0.01). After adjustment for age, smoking, and caffeine, the rate ratio of Parkinson's disease for the highest quartile of uricemia compared with the lowest was 0.43 (95% confidence interval: 0.18, 1.02; p(trend) = 0.017). This association was stronger in analyses excluding cases diagnosed within 4 years (median) from blood collection (rate ratio = 0.17, 95% confidence interval: 0.04, 0.69; p(trend) = 0.010). These results suggest that high plasma urate concentrations may decrease the risk of Parkinson's disease, and they raise the possibility that interventions to increase plasma urate may reduce the risk and delay the progression of Parkinson's disease.     

Serum cholesterol levels and the risk of Parkinson's disease

Several recent findings suggest a role of lipid and cholesterol metabolism in the pathogenesis of Parkinson's disease. Therefore, the authors examined the association between serum levels of cholesterol and the risk of Parkinson's disease in the prospective, population-based Rotterdam Study among 6,465 subjects aged 55 or more years with repeated in-person examination and on average 9.4 years of follow-up (1990-2004). Higher serum levels of total cholesterol were associated with a significantly decreased risk of Parkinson's disease (age- and sex-adjusted hazard ratio per mmol/liter increase in cholesterol = 0.77, 95% confidence interval: 0.64, 0.94), with evidence for a dose-effect relation. The association was restricted to women and remained unchanged after adjustment for multiple potential confounders. These findings may indicate a role of lipids in the pathogenesis of Parkinson's disease. Alternatively, they could reflect the strong correlation-especially in women-between levels of serum cholesterol and the antioxidant coenzyme Q10. If confirmed, this would provide further support for an important role of oxidative stress in the pathogenesis of Parkinson's disease.     

Shift work, risk factors and cardiovascular disease.

The literature on shift work, morbidity and mortality from cardiovascular disease, and changes in traditional risk factors is reviewed. Seventeen studies have dealt with shift work and cardiovascular disease risk. On balance, shift workers were found to have a 40% increase in risk. Causal mechanisms of this risk via known cardiovascular risk factors, in relation to circadian rhythms, disturbed sociotemporal patterns, social support, stress, behavior (smoking, diet, alcohol, exercise), and biochemical changes (cholesterol, triglycerides, etc) are discussed. The risk is probably multifactorial, but the literature has focused on the behavior of shift workers and has neglected other possible causal connections. In most studies methodological problems are present; these problems are related to selection bias, exposure classification, outcome classification, and the appropriateness of comparison groups. Suggestions for the direction of future research on this topic are proposed.