A case cohort study of suicide in relation toexposure to electric and magnetic fields amongelectrical utility workersDalsu Baris, Ben G Armstrong, Jan Deadman, Gilles Theriault

AbstractObjectives-This case cohort study exam-ines whether there is an associationbetween exposure to electric and mag-netic fields and suicide in a population of21 744 male electrical utility workers fromthe Canadian Province of Quebec.Methods-49 deaths from suicide wereidentified between 1970 and 1988 and asubcohort was selected comprising a 1%random sample from this cohort as abasis for risk estimation. Cumulative andcurrent exposures to electric fields, mag-netic fields, and pulsed electromagneticfields (as recorded by the POSITRON meter)were estimated for the subcohort andcases through a job exposure matrix. Twoversions of each of these six indices werecalculated, one based on the arithmeticmean (AM), and one on the geometricmean (GM) of field strengths.Results-For cumulative exposure, rateratios (RR) for all three fields showedmostly small non-significant increases inthe medium and high exposure groups.The most increased risk was found in themedium exposure group for the GM ofthe electric field (RR = 2-76, 95% CI1-15-6-62). The results did not differ afteradjustment for socioeconomic state, alco-hol use, marital state, and mental disor-ders. There was a little evidence for anassociation of risk with exposure immedi-ately before the suicide.Conclusion-Some evidence for an asso-ciation between suicide and cumulativeexposure to the GM of the electric fieldswas found. This specific index was notinitally identified as the most relevantindex, but rather emerged afterwards asshowing the most positive associationwith suicide among the 10 indices studied.Thus the evidence from this study for acausal association between exposure toelectric fields and suicide is weak. Smallsample size (deaths from suicide) andinability to control for all potential con-founding factors were the main limita-tions of this study.

(Occup Environ Med 1996;53:17-24)

Keywords: electromagnetic fields; suicide; case cohort

An association between suicide and overheadand underground high voltage power lines was

first suggested by Reichmanis et al.' Estimatesof residential exposures to electric and mag-netic fields of 598 suicide victims were foundto be significantly higher than that of controls.Perry et at2 conducted a study with the same598 cases of suicide. Measurements of mag-netic fields were made at suicide and controladdresses. More suicide than control measure-ments were above the median (P < 0-01) andmean values of measured electromagneticfields for suicide residences were significantlyhigher than those of controls. Perry and Pearl3also found that among residents of high riseapartments in England, significantly morepeople who had depressive illness than con-trols, had been living close to electric cables.McDowell4 followed up 8000 people inEngland who were living within 30 m of elec-trical transmission lines. He found a standard-ised mortality ratio (SMR) for suicide of 0-75,providing no support for an association withelectromagnetic fields. In another British sur-vey Dowson and Lewith5 showed that peoplewho were living close to 132 kV overheadpower lines were more likely to haveheadaches, migraines, and depression thanthose in the control group. Baris andArmstrong6 found that men described as elec-trical workers on their death certificates didnot have an increased rate of suicide.The results of these studies are subject to

question because of their limited methodologyand exposure measurements. Recently twomore sophisticated studies have been pub-lished. Poole et at7 reported about a twofoldincrease in the prevalence of depressive symp-toms among residents living near power lines.Exposures to magnetic fields were not mea-sured, but the association was not explainedby demographic variables associated withdepression. Later, McMahan et at8 investi-gated the depressive symptoms in 152 femaleresidents living close to overhead transmissionlines in Orange County, California. No signifi-cant difference was found in depressive scoresin residents adjacent to overhead transmissionlines compared with subjects living one blockaway. Spot measurements taken at front doorswere used to assess the exposures to magneticfields.An association between suicide and expo-

sure to electromagnetic fields is made moreplausible by observations that electromagneticfields may affect the nervous system andneuroendocrine function. Specifically, electro-magnetic fields have been found to reduce theproduction of melatonin hormone by the

Occupational and Environmental Medicine 1996;53:17-24 17

Department ofOccupational Health,Faculty ofMedicine,McGill University,Montreal, CanadaD BarisB G ArmstrongJ DeadmanG TheriaultAtomic EnergyControl Board,Radiation andEnvironmentalProtection Division,Ottawa, CanadaD BarisEnvironmentalEpidemiology Unit,London School ofHygiene and TropicalMedicine, LondonB G ArmstrongCorrespondence to:Dr D Baris, Atomic EnergyControl Board, Radiationand EnvironmentalProtection Division,PO Box 1046, Station B,280 Slater Street, Ottawa,Canada KlP 5S9.Accepted 3 August 1995

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Baris, Armstrong, Deadman, Thiriault

pineal gland and disturb its circadianrhythm.9-10 There is substantial evidence thatdisruption in the normal circadian rhythm ofpineal melatonin secretion is associated withdepression." -'4 Finally there is firm evidencethat depressive illness is strongly associatedwith suicide.'We conducted a case cohort study to inves-

tigate the association between suicide andoccupational exposure to electric fields, mag-netic fields, and pulsed electromagnetic fields.The study base comprised a cohort of 21 744electrical utility workers followed up from1970 to 1988. This cohort was one of threecohorts in which cancer incidence was investi-gated in the "Canada-France" case-controlstudy.'6 Two other cohorts were not used inour case cohort study because the agreementfor the Canada-France study was only forstudying cancer incidence and not all thecohorts were followed up for mortality.

MethodsDESIGN AND STUDY POPULATIONThe study follows the case cohort design.'7This is similar to a nested case-control design inincluding all cases and a sample of the cohort.The sample (subcohort) is a random one cho-sen from all cohort members, instead of con-trols matched to cases from survivors to theage of death of the case, and the methods ofanalysis are different. Case cohort design isknown as valid and more efficient than nestedcase-control design.'7 Also the random sampleof the entire cohort (subcohort) can be used asa control group for studying several diseasessimultaneously.As described elsewhere,'8 deaths in the

entire cohort were identified from the com-pany records if the worker died while an activeemployee, or through the retirement system ifhe had left the company but was entitled toclaim benefits. Those who left the companywithout being qualified for a pension weretraced by provincial sources. We found 49workers who had suicide as underlying causeof death (ICD-9 950 0-959 0) on their deathcertificates.The subcohort of 217 subjects was selected

as a 1% random sample of the entire cohort.Two were excluded because their job historieswere not available, leaving 215 subjects eligi-ble for the analysis.

ESTIMATION OF EXPOSUREWe obtained the complete job histories of thesubcohort members and cases from the com-pany records. This information included jobtitle, start and end date of each job, and jobcode. A job exposure matrix comprising esti-mates of exposure to 60 Hz electric, magneticand pulsed electromagnetic fields for each jobheld in the company had been previously con-structed for a case-control study of cancer. 16 Inthe job exposure matrix, for each job category,arithmetic means (AM) and geometric means(GM) of electric fields and magnetic fieldswere estimated from POSITRON dosimetersworn for a week by a random sample of work-

ers. The AM tends to reflect occasional excur-sions in very high fields. The GM is lessaffected by such peaks, and reflects long peri-ods in moderately raised fields.'9 The distribu-tion of exposure to pulsed electromagneticfields was extremely highly skewed. To dealwith this, exposure to pulsed electromagneticfields was calculated in each job category ofthe job exposure matrix as the proportion ofsubjects measured with weekly AM of pulsedelectromagnetic fields greater than 100 partsper billion (proportion >100 ppb).20 This wasused as a unit of exposure for pulsed electro-magnetic fields in the analysis. The GM ofpulsed electromagnetic fields was not used, as itwas highly dependent on the value assumedfor periods during which no pulsed electro-magnetic field was detected. Finally, the jobexposure matrix was linked to each subject'swork history to calculate their cumulative andcurrent exposure for cases and the members ofthe subcohort.We first considered long term exposure as a

risk factor for suicide. The hypothesis behindthis was that chronic exposure might causeirreversible disruption in circadian rhythm,and this condition might lead first to depres-sion and then to suicide. We used AM andthen GM of the electric and magnetic fields tocalculate two indices of cumulative exposure.The summary indices represent cumulativeexposure to electric fields expressed in Voltsper meter years (V.m- .y) and magnetic fieldsexpressed in microtesla years (,uT.y), equal tothe mean (or GM) over a subject's workinglife, times his duration of employment. Forpulsed electromagnetic fields, the unit ofcumulative exposure was the proportion >100ppb.y.

It is also possible that the effective exposureis that immediately before suicide, rather thanchronic exposure. To examine this hypothesis,we considered current exposure, defined forsuicide as the mean exposure for the year inwhich the suicide occurred. For the subcohort,

Table 1 Demographic description of the subcohort andcases

Subcohort Casesn (%) n (%)

Total 215 (100-00) 49 (100 00)Year of birth:1949 79 (36 74) 9 (18-37)

Year of hire:1979 37 (17 21) 2 (4 08)

Year of death:

A case cohort study of suicide in relation to exposure to electric and magnetic fields among electrical utility workers

current exposure was recalculated for eacide death, as the mean in the yeardeath (see statistical analysis). We exieight cases of suicide from the analysisrent exposure because death occurred alsubjects left the company. This exclusicited the analysis for current exposurecases who were still working before thecide.

For cumulative exposure, three groutdefined: (a) low: median but 75th percentile.For current exposure indices, because

effectively discrete nature of the estexposure, there were less than 10 subjthe medium exposure group. Therefocombined low and medium exposure gand defined only two exposure groupslows: (a) low and medium: 75th percentile.

INFORMATION ON OTHER RISK FACTORS ISUICIDESocioeconomic state was assesseddichotomy: white collar or blue collaron the first job held.By reviewing the company medical fi

obtained for each study subject informal(a) history of mental disorders, (b) lasiable marital state, and (c) alcohol cortion. Medical files were available for all

Table 2 Arithmetic (AM) and geometric (GM)electromagnetic fields (PEMF)

but we were unable to find those of 4-2% ofthe subcohort. As an indication of history ofmental disorders, we abstracted all diagnosesfrom sickness absence records with the ninthinternational classification of diseases codes(ICD-9) 290-310. Information on alcoholconsumption was recorded during the medicalexamination at the time of hire or at periodicexamination. We classified people into threecategories: non-users, users, and unknown.Marital state was usually recorded upon hir-ing. We also recorded any indication of changeof marital state. If no further information wasfound, marital state at the time of hiring wasused as the last available marital state.

STATISTICAL ANALYSISStandard methods of relative risk (rate ratio orproportional hazard, (RR)) regression analy-sis2' adapted for the case cohort'7 were used toobtain suicide RRs for groups defined byexposure. We used the EPICURE computer pro-gram22 for this purpose. The analysis implicitlycontrols for confounding by age. Confoundingby other factors was controlled by enteringadditional variables into the regression mod-els. It is possible that depression might be anintermediate variable on the causal pathwaybetween exposure and suicide, as well as aconfounder. We did not use any special ana-lytical techniques to deal with this situation,but we reported results both with and without

mean exposures to 60 Hz electric and magnetic and pulsed

PEMFMagneticfields Electric fields worker

Worker (PT) (V/m) weeksweeks > 100 ppb*

Job group (n) AM GM AM GM AMJobs considered initially to have background exposure:

Blue collar jobs 15 0-15 0-03 5-02 1-28 23-00White collar jobs 24 0-16 0-06 5-76 1-33 0-00

Jobs considered initially likely to be exposed abovebackground levels:Hydroelectric generation:

Equipment electrician 20 0-99 0-23 18-21 1-59 33-30Equipment mechanics 24 0-77 0-18 14-46 1-45 33-30Foremen 9 0-50 0-07 12-42 0-98 37-50Operator 11 1-56 0-67 6-34 1-36 25-00

Nuclear generation:Equipment electricians 6 0-19 0-05 2-82 0-81 0-00Operator 17 0-13 0-05 2-52 0-60 0-00

Diesel generation:Operator 11 0-32 0-12 4-82 1-05 40-00

Transmission:Splicer 12 1-79 0-24 15-79 1-28 83-30Linemen 18 0-60 0-08 57-99 2-41 81 22

Substation:Equipment electrician 29 2-36 0-24 52-13 1-84 42-10Equipment electrician (735 kV) 22 1-78 0-54 122-38 3-62 44-44Maintenance worker, civil

and mechanical engineer 23 1-05 0-09 31-75 1-92 4-80Operator (mobile) 16 1-17 0-23 12-04 1.19 71-40Operator (fixed) 12 1-78 0-76 36-89 2-06 16-60Technician 18 1-60 0-21 8-63 1-41 14 20

Distribution:Emergency men 8 0-50 0-07 12-71 1-84 60-00Foremen, overhead lines 5 0 16 0 09 5-77 1-06 100-00Foremen, underground lines 6 0-14 0-06 3-02 0-90 100-00Linemen (contact and hotstic) 39 0-37 0-06 83 18 2-36 70-50Linemen (contact) 24 0-83 0-13 123-39 2-45 70-50Meter installer 10 0-42 0-08 5-48 1-52 37-54Meter reader 14 0-17 0-05 10-03 2-48 0-00Splicer, distribution 18 1-87 0-12 9-73 1-63 92-80Tree trimner 4 0-34 0-05 37-51 3-40 50-00

Others:Estimator 10 0-13 0-06 4-31 1-25 0-00Instructor 6 0-17 0-06 2-83 1-00 0-00Licensed electricians 9 0-87 0-19 12-52 1-09 20-00Operator, dispatcher 10 0-09 0-04 3-16 1-08 0-00Technician, telecommunication 11 0-44 0-11 5-12 1-07 50-00

*Percentage of subjects measured with weekly mean > 100 ppb.

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Baris, Armstrong, Deadman, Thiriault

Table 3 The association of electric and magnetic pulsed electromagneticfields (PEMFs) with known risk factors or suicideSubjects (%) in the subcohort with exposure level> median for cumulative exposure

Subjects (%) in the subcohort with exposure level> 75th percentile for current exposure

Risk factor exposure

Electic fieldsAM GMn (%o n(%Ono> median) > median)

MagneticfieldsAM GMn (o n (o) median) > median)

PEMFs * Electric fields Magnetic fields PEMFs *AM AM GM AM GM AMn (%o n ((%/ 75th n (% >75th n (%o 75th n (%/ 75th n (0o 75th> median) percentile) percentile) percentile) percentile) percentile)

Socioeconomic state (first job):White collar 20 (27-9)Blue collar 88 (61-5)

Alcohol use:No 26 (50-0)Yes 69 (50-7)Unknown 13 (37-0)

Last known marital state:Single 68 (53-5)Married 27 (38-0)Unknown 13 (77-1)

Mental disorders:No 88 (47-3)Yes 12 (60-0)Unknown 8 (88-9)

*Unit of exposure = workers (%) ml

30 (41-7) 16 (22-1) 24 (28-3)79 (55-9) 92 (64-3) 84 (58-8)26 (50-0) 22 (43-3) 22 (43-3)72 (50-9) 74 (54-4) 75 (55-1)11 (40-7) 12 (44-4) 11 (40-7)

1 (1-4) 1 (1-4)109 (76-2) 52 (36-3)25 (47-5) 12 (23-1)76 (55-9) 37 (27-2)9 (32-3) 4 (14-8)

66 (51-9) 69 (54-3) 69 (54-3) 63 (49-6) 27 (21-6)31 (43-7) 26 (36-6) 26 (36-6) 36 (50-7) 20 (28-2)12 (70-6) 13 (76-5) 13 (76-5) 11 (64-7) 6 (35-3)88 (47-1) 88 (47-1) 87 (46-7)14 (70-0) 12 (60-0) 13 (75-0)7 (77-8) 8 (88-9) 8 (88-9)

easured who had weekly mean > 100 ppb.

92 (49-5) 44 (23-6)11 (55-0) 5 (25-0)7 (77-8) 4 (44-4)

2 (2-7) 1(1-4) 1(1-3) 0 (0-0)60 (42-9) 57 (39-9) 54 (37-6) 53 (37-1)13 (25-0) 13 (25-0) 13 (25-0) 14 (26-9)46 (33-8) 42 (30-9) 38 (27-9) 36 (26-5)3 (11-1) 3 (11-1) 4 (14-8) 3 (11-1)

31 (27-4) 35 (27-5) 29 (22-8) 33 (26-0)25 (35-2) 19 (26-8) 20 (28-1) 16 (22-5)6 (35-3) 4 (23-5) 6 (35-3) 4 (23-5)

51 (27-4) 50 (26-9) 45 (24-2)8 (40-2) 6 (30-0) 7 (35-0)3 (35-3) 2 (22-2) 3 (33-3)

45 (24-2)4 (20-0)4 (44-4)

adjustment for variables associated withdepression (see discussion). Cumulative andcurrent exposure were treated as time depen-dent in the analysis. Thus we computed eachsubcohort member's cumulative and currentexposures at each age of death of a case. Afixed reference age was required for the tabu-lations by these variables to give a generalimpression of frequencies in exposure groups.The date of death for cases and the date corre-sponding to one year before the date of endingfollow up for the members of the subcohortwere used to compute the fixed reference agefor each subject.

ResultsTable 1 shows the distribution of demographicand basic employment variables. Cases hadsomewhat earlier years of birth and years ofhire than subcohort members. Table 2 showsthe job exposure matrix. The matrix consistedof rows of grouped job titles that wereexpected to have similar exposures, andcolumns of corresponding mean exposures toelectric, magnetic, and pulsed electromagneticfields. Table 3 shows the association of cumu-lative exposure to magnetic and electric fieldswith known risk factors for suicide (% of sub-jects in the subcohort with exposure level>,median), to assess potential for confound-

Table 4 Rate ratios (RR) for suicide by socioeconomic state, alcohol use, marital state,and mental disorders

Subcohort Cases

n (/o) n (Go) RR (95% CI)Socioeconomic state (first job):

White collar 72 (33-5) 11 (22 5) 1-00Blue collar 143 (66-5) 38 (77-5) 1-88 (0-89-3-98)

Alcohol consumption:No 52 (24-2) 15 (30-6) 1-00Yes 136 (63-3) 21 (42-9) 0-55 (0-25-1-18)Unknown 27 (12-6) 13 (26-5) 1-43 (0-57-3-58)

Last known mantal state:Single 127 (59 1) 29 (59-2) 1-00Married 71 (33-0) 16 (32 7) 0-86 (0-41-0-78)Unknown 17 (8-0) 4 (7-1) 0-63 (0-17-2-32)

Mental disorders (ICD-9, 290-310):No 186 (86-5) 16 (32-7) 1-00Yes 20 (9-3) 32 (65-3) 15-17 (676-34 02)Unknown 9 (4-2) 1 (0-0) 1-11 (0-12-10-02)

ing. Broadly, exposure was higher among bluecollar workers than among white collar work-ers. Exposure among alcohol users was verysimilar to that among non-users. The singleworkers showed greater exposure than marriedworkers. Exposure was also higher amongworkers diagnosed with mental disorders thanamong workers with no diagnoses of mentaldisorders.

Table 3 shows the association of currentexposure to the fields with known risk factorsfor suicide (% of subjects in the subcohortwith exposure level ) 75th percentile). Thepattern was similar to that for cumulativeexposure, except that the married workersshowed greater exposure than single workers.

Table 4 shows the rate ratios for suicide bythese potential confounding factors (socioeco-nomic state, alcohol use, marital state, andmental disorders). Blue collar workers, singleworkers, and especially workers with diagnosisof mental disorders had higher risk of suicide.

Table 5 shows the correlations between theindices of the exposure calculated from thesubcohort members at their final exposure lev-els. Seventy five per cent of the correlationsreported were equal to or below 0 50. The twohighest correlations were between (a) the AMsand GMs of the electric fields of current expo-sure (r = 080), and (b) between the GMs ofthe electric fields of cumulative and currentexposures (r = 0.79).CUMULATIVE EXPOSURETable 6 shows the RRs for suicide by cumula-tive exposure to fields. Unadjusted RRs for allthree fields showed mostly small increases inthe medium and high exposure groups.Adjustment for socioeconomic state, alcoholuse, marital state and mental disorders gener-ally resulted in reduced RRs.The most notable increase was found in the

medium exposure group for GMs of electricfields (RR = 2-76, 95% CI 1-15-6-62),although the high group showed a lessincreased rate (RR = 1-96, 95% CI0-65-5-91). This pattern remained afteradjustment for the potential confounding

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A case cohort study of suicide in relation to exposure to electric and magnetic fields among electrical utility workers

Table 5 Correlations between exposure indicesCUMELAM CUMMGAM CUMPEMF-AM CUMELGM CUMMGGM CURELAM CURMGAM CURPEMF-AM CURELGM CURMGGM

Cumulative exposure:Electric fields-AM(CUMELAM) 1.00

Magnetic fields-AM(CUMMGAM) 0-20 100

Pulsedelectromagneticfields-AM(CUMPEMF-AM) 0 77 0-42 1 00

Electric fields-GM(CUMELGM) 0-72 0-02 0-50

Magnetic fields-GM(CUMMGGM) 0 05 0-74 0-09

Current exposure:Electric fields-AM(CURELAM) 0 55 0-07 0-34

Magnetic fields-AM(CURMGAM) 0-06 0-41 011

Pulsedelectromagneticfields-AM(CURPEMF-AM) 0 46 0-22 0-62

Electric fields-GM(CURELGM) 0 43 -0-04 0-25

Magnetic fields-GM(CURMGGM) -0 03 0-43 0 06

1-00

-0-07 1*00

0-73 0-05 1-00

0-15 0-52 0-32 1-00

0-52 0-17 0-67 0-42

0-80 -0-04 0-79 0-18

-0-01 0-71 0-12 0-71

Table 6 Relative risk estimates (95% CIs) for suicide in relation to cumulative exposure to electric, and pulsed electromagnetic fieldsRate ratios (95% CIs)

Adjustedforsocioeconomic

Adjusted for stateAdjustedfor socioeconomic akohol use,

Subjects (n) socioeconomic state, marital state,state alcohol use, and mental

Sub cohort Cases Unadjusted (first job) marital state disordersElectric fields (V/m) (AM):

136-10 and 308-60 54 13 1-49 (0-63-3-52) 1-10 (0-43-2-81) 1-25 (0 46-3-42) 1-68 (0-35-8-01)

Electric fields (V/m) (GM):23-10 and 40 30 54 13 1-96 (0-65-5-91) 1-61 (0-53-4-91) 223 (0-64-7-77) 1-77 (0 36-849)

Magnetic fields (AT) (AM):4-53 and 10-36 54 15 1-34 (0 60-3 02) 0-89 (0-36-2-19) 0 79 (0-28-2-17) 0-36 (0 09-1-99)

Magnetic fields (AT) (GM): 1-25 and 2-08 55 11 1-21 (0 48-3-00) 0-97 (0 38-2-46) 1-85 (0 29-2 48) 0-48 (0 09-2 50)

Pulsed electromagneticfields (AM)*:1 10 and 640 54 19 1 91 (0-85-4-32) 1-32 (0 47-3 75) 1-50 (0 50-4 53) 1 23 (0 27-5 70)

*Unit of exposure workers (%) measured who had weakly mean exceeding 100 ppb.

Table 7 Relative risk estimates (95% CIs) for suicide in relation to cumulative exposure to electric, and pulsed electromagnetic fieldsRate ratios (95% CIs)

Adjustedforsocioeconomic

Adjustedfor stateAdjustedfor socioeconomic alcohol use,

Subjects (n) socioeconomic state marital state,state alcohol use, and mental

Sub cohort Cases Unadjusted (first job) marital state disordersElectric fields (V/m) (AM)*:

10-60 53 10 1-14 (0-52-2 54) 0-92 (0 40-2-15) 1-23 (0-50-3-01) 1 20 (0-32-4-51)

Electric fields (V/m) (GM)*: 1-50 62 14 1-45 (0 70-3-00) 1-21 (0-55-2-66) 1-63 (0-71-3-77) 0 84 (0 26-2 71)

Magnetic fields (uT) (AM)*:0 37 58 14 1-58 (0 76-3-28) 1-33 (0 60-2-97) 1-62 (0 69-3 80) 0-94 (0 25-3 60)

Magnetic fields (uT) (GM)*:0-07 55 11 1-10 (0 50-2 37) 0-86 (0-37-1-98) 0 91 (0-38-2 17) 0 69 (0-19-2 48)

Pulsed electromagneticfields (AM)*t:40 53 11 1-52 (0-73-3 16) 1 27 (0-57-2 82) 1-64 (0 70-3-87) 2 06 (0 50-8 35)

*Because of the effectively discrete nature of estimated current exposure (one of the 32 job categories) the medium group (> median, < 75th percentile) group wassmall, and combined with the low (< median) group.tUnit of exposure = % workers measured who had weakly mean exceeding 100 ppb.

1*00

0-45

0-25

1-00

0-04 1-00

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Bans, Armstrong, Deadman, Theiault

factors already mentioned. When the mediumand high exposure groups were combined theadjusted RR was 2-56 (95% CI 0 87-7-58).

Given the possibility that mental disorderscould be both a confounder and an intermedi-ate variable, we reported the RRs adjusted forall confounders except mental disorders. TheRRs were slightly different, lower or higherdepending on the indices, from the RRsadjusted for all confounders. The highest RRwas again found for GMs of electric fields (RR= 3-10, 95% CI 1-18-8-21).

CURRENT EXPOSURETable 7 shows the association of suicide withcurrent exposure to fields. Unadjusted RRs forall three fields showed mostly small increasesin the high exposure groups. Adjustment forsocioeconomic state only or adjustment foralcohol use and marital state did not substan-tially change the RR estimates. The slightlyincreased risk disappeared when additionaladjustment was made for mental disorders,except for pulsed electromagnetic fields (RR= 2-06, 95% CI 0 50-8-35).

DiscussionFor cumulative exposure, this study showed;(a) an increased risk of suicide for the mediumexposure group by GMs of electric fields, butno evidence for a dose-response; (b) a slightlyincreased risk of suicide for AMs of electricfields; (c) no association of suicide with mag-netic fields or pulsed electromagnetic fields.The increased risk of suicide for GMs of

electric fields could not be explained by con-founding by socioeconomic state, alcohol use,marital state, or mental disorders.

For current exposure, our results suggested;(a) a slightly increased risk of suicide withpulsed electromagnetic fields in the high expo-sure group; (b) no association with the otherindices.

Overall, the strongest evidence was forcumulative exposure from electric fields withthe GM of exposure, but there was no evi-dence for dose-response. There was not muchof an association with cumulative exposure forAMs of electric fields and with current expo-sure for GMs of electric fields, although thesetwo indices were highly correlated with GMsof cumulative exposure for electric fields. Oneexplanation for the difference between theRRs for cumulative and current exposure isthe possibility of a stronger effect for a consis-tent exposure over a long period of time.These results may be subject to bias, eitherupwards or downwards. We consider theselater.A comparison of the suicide rate in the

Hydro Quebec workers with that of the gen-eral population was possible from a cohortmortality study covering the same follow upperiod.18 The SMR for suicide for all workersrelative to the Quebec population was 056(49 observed deaths). The workers were clas-sified crudely by the last job held at the com-pany into two exposure groups, backgroundand above background, for electric, magnetic,

and pulsed electromagnetic fields. The SMRsfor the above background groups for each fieldwere higher (AM of the magnetic field 075,AM of the electric field 070, pulsed electro-magnetic fields 075), but remained belowone. Although there may be some healthyworker effect and some under ascertainmentof deaths, these low SMRs do not support theevidence for a causal association.

POSSIBLE SOURCES OF BIASIncomplete case ascertainmentIt is possible that we might have missed somesuicide cases because of certification practice.The scientific literature on the validity of thesuicide diagnosis focuses mainly on the sensi-tivity of suicide certification23-25 estimated at56% to 99%. The specificity of the certifica-tion was always higher than 95%. It seemsunlikely that the certification practice will varyaccording to the exposure. Thus, misclassifica-tion is likely to be non-differential, and wouldtherefore bias the effect towards the nullvalue.26 This is a concern, as our study showedseveral small non-significant associations.

Misclassification of exposureDespite the large number of exposure mea-surements made to create the job exposurematrix, some misclassification of exposure willhave occurred. One source is the precision ofthe mean exposure estimates in the job expo-sure matrix. The confidence intervals of themean exposure estimates that were given else-where'6 suggested that the broad patterns ofexposure were established beyond reasonabledoubt, but there remained considerable uncer-tainty. As well as from the error in estimatingthe means, misclassification of individual peo-ple would have occurred from the variation inexposure levels between workers in the samerow of the job exposure matrix. The maineffect of these misclassifications would be tobias the risk estimates toward the null.

There was an additional uncertainty in theassessment of exposure to pulsed electromag-netic fields due to the inadequate currentknowledge on what situations trigger thepulsed electromagnetic fields channel. Thepulsed electromagnetic fields meters' thirdchannel was designed to reflect high frequency(5-20 MHz) pulses of electromagnetic energy(>200 V/m). The meter apparently respondsin this channel to bursts of walky talky andlorry radio transmissions, as well as to tran-sient pulses produced by switching. Thisuncertainty was discussed in more detail else-where.20

Confounding factorsLack of information on several important riskfactors for suicide including stress, ethnicity,and physical diseases and imperfect measure-ment on the others might have resulted ininadequate control of confounding in ourstudy.

Socioeconomic state was measured accord-ing to the first job as a simple dichotomousvariable. It is possible that misclassification ofsocioeconomic state may have been differen-

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A case cohort study of suicide in relation to exposure to electric and magnetic fields among electrical utility workers

tial for exposure to electromagnetic fields andmay have led to a bias.

Although we obtained information on alco-hol consumption, our data did not identifyalcohol misuse. Alcohol misuse is second onlyto depression as a risk factor for suicide.27 Itwas reported that alcohol misuse has beenfound to be associated with 50% of suicides.28The fact that we did not find any associationbetween alcohol use and suicide suggestsimperfect measurement of this variable, andconsequently imperfect control of confound-ing by alcohol misuse. It is not obvious thatalcohol misuse would be associated withexposure to electric and magnetic fields, atleast after stratifying by socioeconomic state.Our data show slightly lower risk among

married people. This result is compatible withthe existing knowledge, as reported by Smithet al,29 that married people have lower suiciderates than people who have never married orwho have divorced. Marital state upon hiringwas usually recorded as single in our study. Ifthe worker had changed his state and if thischange had not been recorded in the files,these workers could have been misclassified.Thus, this non-differential misclassificationwould have reduced the risk of suicide amongthose classified as single. Our data was toolimited to identify divorced or widowedpeople. Again, there is a possible failure tocompletely control confounding by maritalstate.

History of mental disorders is a difficult riskfactor to interpret in this study. Mental disor-ders are considered to be the major determi-nant of suicidal behaviour.30 Schizophrenia,anxiety, depression, alcoholism, and majoraffective and adjustment disorders are themost common conditions found in suicidedeaths in general. Several studies have sug-gested that the history of mental disordersamong people who committed suicide rangesbetween 50% and 90% compared with only15% in people who died of other causes.3'This association was confirmed in our study,in which only 9 3% of the subcohort had atleast one diagnosis of mental disorderrecorded on their medical file, whereas 65-3%of cases had been diagnosed with mental dis-orders before suicide. The most commondiagnoses were anxiety and depression. Thisvery high implied rate ratio of suicide (RR =15-17, 95% CI 6-76-34 02) among subjectswith mental disorder is comparable with otherstudies of suicide.

Thus, if men susceptible to mental disor-ders took disproportionately high or low expo-sure jobs, mental disorders would be aconfounding factor. It is also possible thatdepression might be a factor in the pathway ofthe events leading to suicide after exposure toelectric or magnetic fields. If this were true,controlling for depression as a confoundingfactor would bias the risk estimates toward thenull. We were unable to exclude either con-founding by mental disorders, or mental disor-ders being an intermediate variable. There arespecial and relatively complex analytical tech-niques developed to deal with a situation when

a variable is both a confounder, which shouldbe controlled in the analysis, and an interme-diate variable, which should not be controlledin the analysis.32 Pierce33 noted the complexityof these types of analyses and the requirementsof the strong modelling assumptions, and sug-gested that use of such models could causeconfusion both in reader and investigator.Also, our data on history of mental disorderswas partial, in particular lacking precision ontime of onset. Therefore, we chose the simplerapproach of presenting the risk estimates withand without adjustment for mental disorders.The unadjusted estimates are unbiased if thereis no confounding, and the adjusted estimatesare unbiased if mental disorders are not in thecausal pathway (intermediate variable). Infact, the analysis showed that controlling formental disorders in general had a limitedimpact on the risk estimates (tables 6 and 7),so that interpretation of results depends littleon this issue. Similar comments apply to alco-hol use and marital state.

Sample sizeAnother limitation of this study was the sam-ple size. Small numbers of suicide deathsresulted in wide confidence intervals, espe-cially after eliminating the eight cases from theanalysis of current exposure.A high proportion of deaths from "injuries

undetermined whether accidently or purposelyinflicted" (ICD-9, E980-989) are in fact sui-cide deaths.34 Thus including these wouldhave maximised the sample size at the cost ofsome misclassification. There were only threesubjects with such undetermined causes ofdeath. Thus for clarity, we limited the analysisto deaths coded only as suicide.

ConclusionWe found some evidence for an associationbetween suicide and cumulative exposure tothe GMs of electric fields. This specific indexwas not identified initially as the most relevantindex, but rather emerged after showing themost positive association with suicide amongthe 10 indices studied. Thus the evidencefrom this study for a causal associationbetween exposure to electric fields and suicideis weak. The power of the study was limited bysmall sample size. Additional studies withlarger sample sizes and more refined informa-tion on potential confounding factors wouldbe of interest.

This study was funded by a grant from the National HealthResearch and Development Programme of the Department ofHealth Canada, formerly Health and Welfare Canada, Ottawa.The Quebec component of the Canada-France study whichmade this study possible was funded by Hydro-Quebec. DBwas a one year scholar of the Institute de recherches en sante eten security du travil du Quebec. The authors thank D Cyr, PLTgo, A Belanger, M Gilbert for their valuable assistance.

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Occup Environ Med, together with manyother international biomedical journals, hasagreed to accept articles prepared in accor-dance with the Vancouver style. The style(described in full in the BM7, 24 February1979, p 532) is intended to standardiserequirements for authors.

References should be numbered consec-utively in the order in which they are firstmentioned in the text by Arabic numeralsabove the line on each occasion the refer-ence is cited (Manson' confirmed otherreports2-1 . . .). In future references topapers submitted to Occup Environ Med

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Examples of common forms of refer-ences are:

1 International Steering Committee of Medical Editors,Uniform requirements for manuscripts submitted tobiomedical journals. BrMedJ 1979;1:532-5.

2 Soter NA, Wasserman SI, Austen KF. Cold urticaria:release into the circulation of histamine and eosino-phil chemotactic factor of anaphylaxis during coldchallenge. N EnglJ Med 1976;294:687-90.

3 Weinstein L, Swartz MN. Pathogenic properties ofinvading micro-organisms. In: Sodeman WA Jr,Sodeman WA, eds. Pathologic physiology, mechanismsof disease. Philadelphia: W B Saunders, 1974:457-72.

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among electrical utility workers.exposure to electric and magnetic fields A case cohort study of suicide in relation to

D Baris, B G Armstrong, J Deadman and G Thriault

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