Case-control studies of cardiovascular medications as risk factors for clinically diagnosed depressive disorders in a hospitalized population

OBJECTIVE

Certain medications used in cardiovascular therapeutics may contribute to the etiology of substance-induced mood disorders. These medications include digoxin, angiotensin converting enzyme (ACE) inhibitors, beta-blockers, and calcium channel blockers. The objective of this study was to evaluate associations between these drugs and clinical diagnoses of depressive disorders in a population of hospitalized patients.

METHOD

Two case-control studies were conducted. For each study, subjects were selected from a health records data base maintained at the Calgary General Hospital. Selection of subjects in the first study was restricted to those receiving a discharge diagnosis of congestive heart failure and in the second study to subjects receiving a discharge diagnosis of hypertension. In each of these 2 studies, a single case group was selected along with 2 control groups: a psychiatric control group consisting of subjects receiving a psychiatric diagnosis other than a depressive disorder and a nonpsychiatric control group receiving no psychiatric diagnoses. Drug exposures and other variables were recorded from a chart review.

RESULTS

Exposures to digoxin, beta-blockers, and calcium channel blockers were not associated with depressive diagnoses. An association was observed, however, for ACE inhibitors. An elevated odds ratio (OR) was observed in each case-control study and was stronger in female subjects and subjects over the age of 65.

CONCLUSIONS

This is the first reported epidemiological evidence of an association between ACE inhibitors and depressive disorders. The design of this study does not permit a determination of whether the observed association was causal. Additional studies are needed.

Receptor binding and internalization of a water-soluble (1-->3)-beta-D-glucan biologic response modifier in two monocyte/macrophage cell lines

Glucan phosphate, a water-soluble, chemically defined (1-->3)-beta-D-glucan biologic response modifier, has been reported to exert antisepsis activity and accelerate wound healing. In this study we describe the specific binding of glucan phosphate to human and murine monocyte/macrophage cell lines, U937 and J774A.1, respectively. At 37 degrees C, equilibrium binding was rapidly achieved, i.e., within 1 min. In U937 cells, binding occurred with an affinity (Kd) of 37 microM and a Bmax of 65 x 106 binding sites/cell at 37 degrees C. In J774A.1 cells, glucan phosphate bound with an affinity (Kd) of 24 microM and a Bmax of 53 x 106 binding sites/cell at 37 degrees C. In both cases there was insignificant nonspecific binding. We further demonstrated that bound glucan phosphate cannot be displaced by a 50-fold excess of unlabeled ligand, suggesting internalization of glucan phosphate. Transmission electron microscopy showed significantly increased cytoplasmic vacuolization and significantly decreased mitotic activity in glucan phosphate-treated U937 cells compared with that in untreated cells. Pullulan, a random coil alpha-(1-->4)-(1-->6)-linked glucose polymer that served as a control, did not compete for the same binding site as glucan phosphate in either cell line, indicating the specificity of the binding site for (1-->3)-beta-D-glucans. We conclude that water-soluble pharmaceutical grade (1-->3)-beta-D-glucan phosphate specifically binds to and is internalized by U937 and J774A.1 cells.

Receptor binding and internalization of a water-soluble (1-->3)-beta-D-glucan biologic response modifier in two monocyte/macrophage cell lines

Glucan phosphate, a water-soluble, chemically defined (1-->3)-beta-D-glucan biologic response modifier, has been reported to exert antisepsis activity and accelerate wound healing. In this study we describe the specific binding of glucan phosphate to human and murine monocyte/macrophage cell lines, U937 and J774A.1, respectively. At 37 degrees C, equilibrium binding was rapidly achieved, i.e., within 1 min. In U937 cells, binding occurred with an affinity (Kd) of 37 microM and a Bmax of 65 x 106 binding sites/cell at 37 degrees C. In J774A.1 cells, glucan phosphate bound with an affinity (Kd) of 24 microM and a Bmax of 53 x 106 binding sites/cell at 37 degrees C. In both cases there was insignificant nonspecific binding. We further demonstrated that bound glucan phosphate cannot be displaced by a 50-fold excess of unlabeled ligand, suggesting internalization of glucan phosphate. Transmission electron microscopy showed significantly increased cytoplasmic vacuolization and significantly decreased mitotic activity in glucan phosphate-treated U937 cells compared with that in untreated cells. Pullulan, a random coil alpha-(1-->4)-(1-->6)-linked glucose polymer that served as a control, did not compete for the same binding site as glucan phosphate in either cell line, indicating the specificity of the binding site for (1-->3)-beta-D-glucans. We conclude that water-soluble pharmaceutical grade (1-->3)-beta-D-glucan phosphate specifically binds to and is internalized by U937 and J774A.1 cells.

Self-reported depressive symptoms following treatment with corticosteroids and sedative-hypnotics

OBJECTIVE

To evaluate associations between exposure to corticosteroids or sedative-hypnotic medications and incident self-reported depressive symptoms in medical inpatients.

METHOD

The study utilized a prospective cohort design, focusing on acute depressive symptoms developing soon after medication exposure. The incidence of self-reported depressive symptoms was evaluated using a modified version of the Center for Epidemiological Studies Depression Rating Scale (CES-D). The incidence of depressive symptoms in subjects newly exposed to corticosteroids and sedative-hypnotics was compared to that of a nonexposed comparison cohort.

RESULTS

The incidence of self-reported depressive symptoms was elevated in subjects newly exposed to corticosteroids (Risk Ratio = 3.10), although the association did not attain statistical significance (p = .07). The risk ratio for sedative-hypnotic exposure was 4.18, a statistically significant finding (p = .02). As expected, incident self-reported depressive symptoms were also associated with several psychosocial variables. However, the data did not suggest that the observed associations between drug exposures and depressive symptoms were due to confounding by psychosocial or illness-related variables.

A case-control study of corticosteroid exposure as a risk factor for clinically-diagnosed depressive disorders in a hospitalized population

OBJECTIVE

Depressive symptoms may be a side effect of exogenous corticosteroids. However, the literature does not confirm that corticosteroid exposure is associated with the occurrence of depressive disorders. The objective of this study was to determine whether or not corticosteroid exposures are associated with clinical diagnoses of depressive disorders in hospitalized patients.

METHOD

The study used a case-control design. Cases and 2 control groups were selected from a health records case summary database maintained at the Calgary General Hospital. Additional data were collected by chart review.

RESULTS

The analysis reproduced associations between depressive diagnoses and several psychosocial and biological risk factors. However, the data did not suggest that corticosteroids were associated with an elevated risk of depressive diagnoses. In fact, odds ratios for corticosteroid exposure were less than 1, consistent with a protective effect.

CONCLUSIONS

Although corticosteroids may produce depressive symptoms as a side effect, corticosteroid exposures are not associated with an elevated risk of clinically diagnosed depressive disorders in hospitalized patients. There are several possible explanations for this. Depressive syndromes associated with corticosteroid exposure may not clinically resemble depressive disorders, and may not warrant a diagnosis of a depressive disorder. Alternatively, clinicians may not identify and formally diagnose depressive disorders caused by corticosteroids.

Self-reported depressive symptoms in association with medication exposures among medical inpatients: a cross-sectional study

OBJECTIVE

To evaluate associations between exposure to three classes of medications (angiotensin converting enzyme inhibitors, calcium channel blockers, and corticosteroids) and self-reported depressive symptoms.

METHOD

The study utilised a cross-sectional study design in a sample of medical inpatients.

RESULTS

Associations between self-reported depressive symptoms and exposure to angiotensin converting enzyme inhibitors or calcium channel blockers were not observed. However, an association between self-reported depressive symptoms and corticosteroid exposure was identified. The association was strongest in subjects reporting a past history of depression or a family history of depression. The strength of the corticosteroid-depressive symptom association was comparable with that of associations observed for age, poverty and psychosocial stress.

CONCLUSIONS

Depressive symptoms among medical inpatients have a biopsychosocial etiology. Corticosteroid exposure may be a biological risk factor for depressive symptoms in this population.

Effects of agricultural work and other proxy-derived case-control data on Parkinson's disease risk estimates

This study examined the effects on Parkinson's disease risk estimates of exposure misclassification in proxy-derived data on agricultural work, pesticide use, rural living, well water drinking, head trauma, smoking, and family history of Parkinson's disease or essential tremor. The data were collected in 1989 as part of a population-based case-control study of Parkinson's disease in Calgary, Canada. Nondemented cases (n = 130) were selected from a case register of Calgary residents with neurologist-confirmed Parkinson's disease. For each case, two matched (sex and age +/- 2.5 years) community controls were selected by random digit dialing. Forty cases and 77 controls were randomly selected as index respondents. The cases, controls, and one proxy respondent (spouse or offspring) for each index respondent were interviewed using a structured questionnaire. The data were analyzed using conditional logistic regression. Incorporation of proxy-derived data for 30% of the cases or controls, or both, resulted in considerable misclassification of exposure for some variables and, in most cases, attenuation of the odds ratio. The results indicate that pooling dichotomously classified data derived in part from self- and proxy respondents may result in biased estimates of Parkinson's disease risk associated with agricultural, family history, and head trauma factors.

Incidence of hospital-acquired infections associated with caesarean section

A retrospective cohort study was conducted to determine the incidence of post-caesarean infections in a Canadian community teaching hospital using computer algorithms designed for the diagnosis of nosocomial infections. Inferential chart review was done on 1335 women delivered by lower-segment caesarean section (793 primary and 542 secondary) at the Calgary General Hospital between January 1985 and April 1988. The overall infection rates were 42.1 and 46.1% for women delivered by primary and secondary caesarean section, respectively. Incisional surgical wound infection accounted for the largest proportion of post-caesarean infections found. Women delivered by primary caesarean section had significantly higher rates of endometritis, deep surgical wound infection and bacteraemia than those delivered by secondary section. All types of post-caesarean infection, except asymptomatic bacteriuria, caused the duration of the post-partum hospital stay to be significantly increased.

Preventive antibiotic usage in traumatic thoracic injuries requiring closed tube thoracostomy

OBJECTIVE

To evaluate the safety and effectiveness of antibiotics in reducing the infectious complications following closed tube thoracostomy for isolated chest trauma.

DESIGN

Double-blind, randomized clinical trial.

SETTING

Medical school affiliated large urban teaching hospital and trauma center.

PATIENTS

One hundred nineteen of 159 patients over 18 years old presenting to the emergency department requiring closed tube thoracostomy for isolated chest injuries (113 penetrating, 6 blunt).

INTERVENTION

Patients received either placebo or 1 g cefonicid daily intravenously started at chest tube insertion and stopped within 24 h of removal.

MEASUREMENTS AND RESULTS

The development of wound infections, pneumonia (CDC criteria), or empyema; the incidence of adverse events; length of hospitalization. One nonspecific infection was seen in the cefonicid group (1.6 percent) and six respiratory tract infections (10.7 percent) in the placebo group (three empyema, one empyema with pneumonia, two pneumonia) (p = 0.0505; p = 0.0094 [excluding nonspecific infection]). No significant differences with antibiotic use were seen in the duration of chest tube use (p = 0.766), peak WBC counts (p = 0.108), lower peak temperatures (p = 0.063), or length of hospitalization (p = 0.165). Patients who developed infectious complications averaged approximately 8 days longer hospitalization than those without (p < 0.0001).

CONCLUSION

This study showed that patients receiving antibiotics had a significantly reduced rate of infection than did patients administered placebo. No significant adverse events were seen in either group.

Women and exercise participation: the mixed blessings of motherhood

Exercise participation, perceived barriers to exercise, and perceived benefits of exercise were analyzed in a large random sample of urban women ages 20-49 (N = 1,113). Although mothers and women without children perceived similar benefits of exercising, mothers were much less active than women without children. The differences were greatest for women under the age of 40. After age 40, the differences were smaller as a result of the decrease in exercise in women without children. The study also indicated that motherhood itself, rather than the number and ages of children, was a barrier to exercise participation. In general, mothers perceived more barriers to exercising than did women without children. These findings illustrate the differences in opportunities for mothers and women without children due to sociocultural circumstances and have implications for the planning of exercise promotion for mothers.

Reliability of environmental and occupational exposure data provided by surrogate respondents in a case-control study of Parkinson's disease

This study used data provided by 40 non-demented Parkinson's disease patients and 101 community controls, and by their 110 spouses and 31 adult children to assess the reliability of surrogate-provided rural environmental and occupational exposure information on the index subjects. The level of overall raw agreement between the index subjects and the spouse or adult child surrogates varied from 50.0 to 100.0% for the case-surrogate group and from 80.6 to 96.0% for the control-surrogate group. We did not detect significant differences in overall raw agreement between the case-surrogate and control-surrogate groups or between the spouse-surrogate and adult child-surrogate groups, for any of the variables studied. Considering all index subjects and their surrogates, the level of overall raw agreement was 80.3% for well water consumption, 82.3% for farm living, 85.8% for agricultural work, 87.1% for use of pesticides, 87.9% for field crop farming and 91.9% for use of fertilizers. However, the kappa estimates were lower, varying from 0.48 (SE = 0.20) for fertilizer use to 0.66 (SE = 0.11) for crop farming. The level of specific agreement was 52.2% for fertilizer use, 64.0% for pesticide use, 71.4% for agricultural work, 73.9% for crop farming, 80.9% for farm living, and 83.6% for well water consumption. The overall findings of this study support the use, if necessary, of spouses and adult children of index subjects as surrogate respondents in case-control studies of rural environment and occupational exposures and Parkinson's disease and, possibly, other neurologic diseases. Specific agreement seems to be a better index of reliability than overall agreement in studies where exposure is rare.

Childhood and adolescent passive smoking and the risk of female lung cancer

BACKGROUND

Few studies have reported the relationship between passive smoking (PS) in early life and the risk of lung cancer. This study was done to evaluate the risk of female lung cancer from PS, especially that during childhood and adolescence.

METHODS

Using household exposure to tobacco smoke as an estimate of PS, a 1:1 paired case-control study was conducted in Harbin, China. We interviewed 114 female primary lung cancer cases, aged 30-69 years, and their hospital-based controls. The controls were non-cancer patients, selected from the same hospital as the cases, and matched on age (+/- 5 years), residential area and smoking status over their lifetime. There were 59 pairs who ever smoked and 55 pairs who never smoked. Information on PS was collected by residence for each of the following periods: 0-6, 7-14, 15-22, 23-30 and 31-69 years.

RESULTS

Household PS significantly increases the risk of female lung cancer for those exposed at ages 22 or younger, who have ever smoked. The risk was also increased for those non-smoking pairs when exposed under the age of 15 years. Exposure to maternal smoking at ages 14 or younger increased the risk by about 170% (odds ratio, OR 2.7, 95% confidence interval [CI]: 1.49-4.88), but not to paternal smoking (OR 1.40, 95%CI: 0.92-2.50). The risk was highest for those exposed under the age of seven (OR 3.46, 95%CI: 1.80-6.65) and was also significant at ages 7-14 (OR 3.08, 95% CI: 1.62-5.57) and 15-22 (OR 3.10, 95%CI: 1.52-6.31) years. Under the age of 23 years, the OR increased with amount of PS (P < 0.001). Of note, the OR in all five exposure periods for non-smoking pairs were similar to those for all 114 pairs studied.

CONCLUSIONS

Household PS, particularly that during childhood, increases the risk of female lung cancer. The assessment of PS should be done by different periods of exposure.

Drug-induced depression. Incidence, avoidance and management

According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-III-R), drug-induced depression may be classified as an Organic Mood Syndrome, Depressed Type. Unfortunately, the DSM-III-R diagnostic criteria are not sufficiently precise for application in research, and studies of drug-induced depression have rarely utilised these criteria. Research concerned with drug-induced depression is characterised by a number of methodological complications. These include differing definitions of depression, including depression defined as a symptom, a syndrome, or by diagnostic criteria for a specific mental disorder. In addition, patients undergoing pharmacological treatments for medical illnesses are typically exposed to considerable psychosocial stress due to the suffering and disability associated with illness. These psychosocial factors may in themselves precipitate episodes of depression. Due to these complicating factors, sophisticated study designs are required to confirm an aetiological role for medications as risk factors for depression. Unfortunately, adequate studies have rarely been conducted, and much of the literature consists of case reports and clinical observations. Consequently, clinicians are frequently required to make clinical judgements about the aetiology of patients' depressive symptoms in the absence of definitive scientific information about the role of drugs. Nevertheless, a knowledge of the relevant literature will assist clinicians in making reasoned judgements about the aetiology, prevention and management of these disorders.

Neuropsychiatric adverse drug reactions: passive reports to Health and Welfare Canada's adverse drug reaction database (1965-present)

OBJECTIVE

Since 1965, Health and Welfare Canada has operated an adverse drug reaction (ADR) program. The program accepts spontaneous reports of adverse drug reactions, and maintains an ADR database. The purpose of this article is to summarize the Psychiatric ADRs reported to this database since 1965. The nature of the information prohibits its use in the evaluation of epidemiological hypotheses about the etiology of drug-induced mental disorders. However, in an exploratory sense, the contents of the database may contribute to the development of epidemiological hypotheses about the etiology of drug-induced mental disorders. Of particular interest are areas of apparent contradiction between the contents of the database and the clinical literature.

METHODS

The database was searched for reports of ADRs to a group of drugs which have been frequently implicated in causing psychiatric toxicity. All reports characterized as "psychiatric disorders" were down-loaded from the database for the analysis (n = 1822). The reports were further classified into nine categories according to the type of psychiatric symptoms described.

RESULTS

There were several reports of hallucinations caused by methyldopa, and also several reports of benzodiazepine-induced hallucinations and encephalopathy. These reactions have not been described in the literature. Also, there were few reports of digoxin-induced organic depression, and an absence of reports of organic mania induced by H-2 blockers, despite descriptions of these sorts of reactions in the clinical literature.

CONCLUSIONS

Further research is needed to define the neuropsychiatric toxicity associated with medical drugs. Clinicians must continue to consider the potential role of medications in the etiology of psychiatric symptoms.

Exercising at work: barriers to women's participation

Only a minority of women in an urban random sample have the opportunity to exercise at work, and even fewer women use these opportunities. Lack of time and inconvenient times are the major reasons for not participating in exercise programs at work. Exercise programs at work are used by women who are already physically active, suggesting that workplace exercise programs do not serve the needs of women who may need exercise programs most. Multivariate analysis shows that age, having children, lack of energy, and lack of support are significant barriers to women's exercise participation at work. The results of this study suggest a leadership opportunity for on site occupational health nurses in addressing these barriers to workplace exercise.

Parkinson's disease: a test of the multifactorial etiologic hypothesis

We studied the relative etiologic importance upon the development of Parkinson's disease (PD) of occupational exposure to herbicides and other compounds, ionizing radiation exposure, family history of PD and essential tremor, smoking, and history of various viral and other medical conditions. We identified patients (n = 130) with neurologist-confirmed idiopathic PD through contacts with Calgary general hospitals, long-term care facilities, neurologists, the Movement Disorder Clinic, and the Parkinson's Society of Southern Alberta, and selected two matched (by sex and age +/- 2.5 years) community controls for each case by random digit dialing. We obtained lifetime work, chemical, radiation, medical, and smoking exposure histories and family histories of PD and essential tremor by personal interviews, and analyzed the data using conditional logistic regression for matched sets. After controlling for potential confounding and interaction between the exposure variables, using multivariate statistical methods, having a family history of PD was the strongest predictor of PD risk, followed by head trauma and then occupational herbicide use. Cases and controls did not differ in their previous exposures to smoking or ionizing radiation; family history of essential tremor; work-related contact with aluminum, carbon monoxide, cyanide, manganese, mercury, or mineral oils; or history of arteriosclerosis, chicken pox, encephalitis, hypertension, hypotension, measles, mumps, rubella, or Spanish flu. These results support the hypothesis of a multifactorial etiology for PD, probably involving genetic, environmental, trauma, and possibly other factors.

Can drugs cause depression? A review of the evidence

Drug-induced depressive disorders are classified in the DSM-III-R as organic mood syndrome, depressed type. The ability of certain drugs to cause depression is of clinical relevance because organic mood syndrome is a component of the differential diagnosis of depressive symptoms. Consequently, psychiatric textbooks often provide different lists of drugs thought to be capable of causing depression. Strong evidence supporting the existence of causal associations is often lacking. There is no specific drug for which there is definitive evidence of a causal association with depressive symptoms or depressive disorders. Nevertheless, for a number of drugs, the evidence is suggestive, although not conclusively, of a causal association. Despite this, rational decisions about the continuation or discontinuation of drugs can often be made. In this paper, the literature is reviewed and guidelines are suggested for the management of patients with depressive symptoms which may be related to drugs.

Women's social roles and their exercise participation

How women's social roles such as parenthood, marital status and employment status affect their exercise participation, is important for the rational planning of suitable and effective exercise programs for women in different social contexts. A secondary analysis of a large data-base of urban women aged 20-49 (n = 5939) was carried out to determine if social roles, their characteristics and their combinations were related to women's exercise participation. Parenthood and marital status were significantly related to whether women exercise, and among those exercising, all three roles were significantly related to the amount of exercise. Statistical modelling, including all three roles and their interactions, controlling for age and education, showed that with respect to whether women exercise, parenthood affected exercise participation most and that its effect was dependent on age. Of the role characteristics only the number of children and overall satisfaction with daily activities improved the prediction of exercising. With respect to how much women exercise, the effect of parenthood interacted with marital status. Married parents were least likely to exercise very much. Of the role characteristics only overall satisfaction with daily activities improved the prediction of the amount of exercise.

An assessment of the usefulness of demographic data provided by surrogate respondents in a case-control study of Parkinson's disease

This study, based upon data from 40 non-demented Parkinson's disease cases and 101 community controls, and similar data provided by either the spouse (n = 110) or an adult child (n = 31) of each index subject, attempted to assess the usefulness of various demographic data provided by the surrogate respondents for the index subjects. The data were collected by personal interview using a structured questionnaire specifically developed for this study. Ninety-one percent of the index subjects and their surrogates provided information on the annual family income and 98% provided other demographic information. The analysis was done by three groups: the case-surrogates, the control-surrogates and the combined index subject-surrogates, and within each group by the two types of surrogates for the index subjects: the spouse vs adult child. The overall percent agreement between the index subjects and their surrogates varied from moderate for annual family income (54.1%), to good for educational level (61.6%) and to excellent for ethnic origin (82.6%), for age +/- 1 year (97.9%) and for marital status (100.0%). No significant differences in agreement were found for any of these demographic variables either between the case-surrogate group and the control-surrogate group, or between the spouse surrogates and the child surrogates. These findings suggest that spouses and adult children can provide valid information and are equally reliable informants concerning the demographic characteristics of index subjects in a case-control study of Parkinson's disease and, possibly, of other diseases.

Women's exercise participation: the relevance of social roles compared to non-role-related determinants

The objectives of this study were 1) to determine the relationship between women's exercise participation and their social roles as well as characteristics of these roles, and 2) to determine the relative importance of social roles compared to non-role-related determinants (including social support, perceived barriers, interest in exercise, and perceived importance of exercise). A cross-sectional survey was done among 1,113 randomly selected urban women aged 20-49. Social roles did not emerge as a major risk factor for exercise participation. Statistical modelling indicated that whether women exercise was only related to role overload in the presence of the non-role-related determinants. For women exercising, parenthood as well as role overload were related to the amount of exercise in the presence of the non-role-related determinants. These findings have important implications for exercise promotion for women.

Hypertension and its correlates in the Hutterite community of Alberta

The purpose of this study was to determine the prevalence of hypertension and its correlates in the Hutterite population of Alberta. A total of 811 subjects from 38 Hutterite colonies participated in the survey. A self- and interviewer-administered questionnaire gathered information about past medical history, lifestyle habits, and family history. Blood pressure, blood cholesterol, 2 hour postprandial blood glucose and height and weight were also measured. The prevalence of diastolic blood pressure > or = 90 mm Hg was approximately twice that reported in other Canadian surveys: 60% and 30% for the males and females respectively. Half of the participants found to be hypertensive were unaware of their condition and of those aware, 76% were uncontrolled. There were significant correlations between diastolic blood pressure and Body Mass Index (BMI), cholesterol, age and glucose. This study supports the need for the development of culturally appropriate health promotion programs related to hypertension in this population.

Parkinson's disease and exposure to agricultural work and pesticide chemicals

This population-based case-control study of 130 Calgary residents with neurologist-confirmed idiopathic Parkinson's disease (PD) and 260 randomly selected age- and sex-matched community controls attempted to determine whether agricultural work or the occupational use of pesticide chemicals is associated with an increased risk for PD. We obtained by personal interviews lifetime occupational histories, including chemical exposure data, and analyzed the data using conditional logistic regression for matched sets. In the univariate analysis, a history of field crop farming, grain farming, herbicide use, or insecticide use resulted in a significantly increased crude estimate of the PD risk, and the data suggested a dose-response relation between the PD risk and the cumulative lifetime exposure to field crop farming and to grain farming. However, in the multivariate analysis, which controlled for potential confounding or interaction between the exposure variables, previous occupational herbicide use was consistently the only significant predictor of PD risk. These results support the hypothesis that the occupational use of herbicides is associated with an increased risk for PD.