William T. Kaune

A pooled analysis of magnetic fields, wire codes, and childhood leukemia

We obtained original individual data from 15 studies of magnetic fields or wire codes and childhood leukemia, and we estimated magnetic field exposure for subjects with sufficient data to do so. Summary estimates from 12 studies that supplied magnetic field measures exhibited little or no association of magnetic fields with leukemia when comparing 0.1–0.2 and 0.2–0.3 microtesla (&mgr;T) categories with the 0–0.1 &mgr;T category, but the Mantel-Haenszel summary odds ratio comparing >0.3 &mgr;T to 0–0.1 &mgr;T was 1.7 (95% confidence limits = 1.2, 2.3). Similar results were obtained using covariate adjustment and spline regression. The study-specific relations appeared consistent despite the numerous methodologic differences among the studies. The association of wire codes with leukemia varied considerably across studies, with odds ratio estimates for very high current vs low current configurations ranging from 0.7 to 3.0 (homogeneity P = 0.005). Based on a survey of household magnetic fields, an estimate of the U.S. population attributable fraction of childhood leukemia associated with residential exposure is 3% (95% confidence limits = –2%, 8%). Our results contradict the idea that the magnetic field association with leukemia is less consistent than the wire code association with leukemia, although analysis of the four studies with both measures indicates that the wire code association is not explained by measured fields. The results also suggest that appreciable magnetic field effects, if any, may be concentrated among relatively high and uncommon exposures, and that studies of highly exposed populations would be needed to clarify the relation of magnetic fields to childhood leukemia.

Association between childhood acute lymphoblastic leukemia and use of electrical appliances during pregnancy and childhood.

As part of a comprehensive study of residential magnetic field exposure in nine midwestern and mid-Atlantic states, we evaluated the use of appliances by 640 patients with acute lymphoblastic leukemia, 0–14 years of age, diagnosed between 1989 and 1993, and 640 matched control children. Mothers were interviewed regarding use of electrical appliances during their pregnancy with the subject and the childs postnatal use. The risk of acute lymphoblastic leukemia was elevated in children whose mothers reported use of an electric blanket or mattress pad during pregnancy [odds ratio (OR) = 1.59; 95% confidence interval (CI) = 1.11–2.29] but was reduced for use of sewing machines during pregnancy (OR = 0.76; 95% CI = 0.59–0.98). The risk of acute lymphoblastic leukemia was increased with childrens use of electric blankets or mattress pads (OR = 2.75; 95% CI = 1.52–4.98) and three other electrical appliances (hair dryers, video machines in arcades, and video games connected to a television), but the patterns of risk for duration in years of use and frequency of use were inconsistent for most appliances used by children. Risks rose with increasing number of hours per day children spent watching television, but risks were similar regardless of the usual distance from the television. The inconsistency in the dose-response patterns for many appliances, reporting and selection bias, and the lack of an effect for measured 60 Hertz magnetic fields or wire codes in our companion study must be considered before ascribing these associations to exposures from magnetic fields. (Epidemiology 1998;9:234–245)

Magnetic field exposure assessment in a case-control study of childhood leukemia

Epidemiologic evaluation of the relation between magnetic field exposures and cancer depends critically on study design, particularly the methods used for exposure assessment. We incorporated a complex magnetic field exposure assessment protocol into a large incident case‐control study of childhood leukemia. We measured residential magnetic fields using a standard protocol in current and former homes of 638 cases and 620 controls and determined wire codes for 414 case‐control pairs. We chose a time‐weighted average of magnetic field measurements in each eligible home, weighted by the time the subject lived in each home as the main exposure metric for each subject. We found that 24‐hour bedroom magnetic field measurements adequately characterize childrens residential exposure and that measuring other rooms contributes only slightly to the estimate of average residential exposure to magnetic fields. Front door measured fields provide useful exposure information when interior measurements are missing. If feasible, measuring multiple homes in which the subject has resided is preferable to measuring a single home. A similar distribution of wire codes for controls agreeing or refusing to participate in our study implies that risk estimates derived from wire code data will not be influenced by response bias.

Childhood exposure to magnetic fields : Residential area measurements compared to personal dosimetry

We examined the relation between area measurements of residential magnetic fields and personal dosimetry measurements among 64 control children age 2–14 years from the National Cancer Institute-Childrens Cancer Groups nine-state case-control study of childhood leukemia. During a typical weekday, an activity diary was completed, and a 24-hour measurement was obtained in each childs bedroom. According to the activity diaries, children spent more than 40% of the 24 hours in their bedrooms, and 68% of their time at home. We found that at-home personal dosimetry levels were highly correlated with total personal dosimetry levels in children under 9 years (Spearman correlation coefficient, R = 0.94), whereas the correlation was lower in older children (R = 0.59). For all children combined, bedroom 24–hour measurements correlated well with at-home personal dosimetry levels (R = 0.76). The 24-hour bedroom measurement was a useful predictor of both at-home and total personal dosimetry measurements. Particularly for younger children, our data suggest that in-home area measurements predict both current residential and current total magnetic field exposures. This information will be valuable for assessing the validity of exposure assessment in previous and ongoing studies and for developing measurement protocols for future studies.

CHILDHOOD CANCER OCCURRENCE IN RELATION TO POWER LINE CONFIGURATIONS: A STUDY OF POTENTIAL SELECTION BIAS IN CASE-CONTROL STUDIES

Several case-control studies have reported positive associations between childhood cancer and proximity to high-current residential power lines as defined by the Wertheimer-Leeper code. We conducted a study to evaluate whether or not differential nonparticipation of controls as a function of socio-economic status is likely to account for the observed associations. We assessed the relation of annual family income to the Wertheimer-Leeper code in a sample of 392 households in western Washington state, and we evaluated the magnitude of bias that could occur from differential participation of low- and high-income eligible controls. Very-high-current configurations were most frequently located among households with self-reported family income of less than

Alcohol consumption and urinary concentration of 6-sulfatoxymelatonin in healthy women.

15,000 per year, and very-low-current configurations were most frequently located among those with self-reported family income of more than

Reproduction and development in rats chronologically exposed to 60-Hz electric fields

45,000 per year. In a hypothetical case-control study in which: (1) it was assumed that there is no true etiologic relation between power line configurations and cancer occurrence, and (2) controls with very low income were less likely to participate than others, observed (biased) odds ratios ranged from 1.03 to 1.24. If these results are applicable to other areas where case-control studies of cancer in relation to power lines have been conducted, they suggest that relatively lower participation among exposed controls (as a function of very low income) is not likely to account for the elevated risks of 1.5− to 3-fold that have been observed in these previous studies.

Residential wire codes: reproducibility and relation with measured magnetic fields

Consumption of alcoholic beverages may suppress circulating melatonin levels at night, possibly resulting in an increase in circulating estrogen. An increased estrogen burden could increase the risk of breast cancer. This study was designed to investigate whether alcohol consumption is associated with a decrease in nighttime melatonin levels in a group of healthy women. A total of 203 randomly selected healthy women between the ages of 20 and 74 years were recruited for a broader study of the effects of exposure to power-frequency magnetic fields on nocturnal levels of urinary 6-sulfatoxymelatonin. For the purposes of this analysis, data collection consisted of the following during two seasons of the year: (1) an in-person interview, (2) a daily activity diary, and (3) nocturnal urine collection for each of 3 consecutive nights. We found that the nocturnal urinary concentration of the primary metabolite of melatonin (6-sulfatoxymelatonin) decreased in a dose-dependent manner with increasing consumption of alcoholic beverages in the preceding 24-hour period, after taking into account the independent effects on melatonin of age, hours of darkness, use of medications that affect melatonin levels, and body mass index. A categorical analysis revealed no effect of one drink, but a 9% reduction with two drinks, a 15% reduction with three drinks, and a 17% reduction with four or more drinks. It remains unknown whether such a change could affect estrogen levels or breast cancer risk.

A Method for the Exposure of Miniature Swine to Vertical 60 Hz Electric Fields

Abstract Previous studies have raised the possibility of reproductive and developmental changes in miniature swine chronically exposed to a strong 60‐Hz electric field. Two replicate experiments on rats were performed to determine if similar changes could be detected in animals exposed under a comparable regime, which was based on average, induced‐current densities and on the chronology of reproductive development, as dosimetrically and biologically scaled. Beginning at three months of age, female rats of the F0 generation and their subsequent offspring were chronically exposed to a 60‐Hz electric field (100 kV/ m unperturbed) for 19 h/day for the duration of experimentation. After four weeks of exposure, F0 female rats were mated to unexposed male rats during the field‐off period. No significant developmental effects were detected in their litters, confirming our previous results with swine and rats. The F0 females were mated for a second time at 7.2 months of age, and the fetuses were evaluated shortly before term. In the first experiments, the incidence of intrauterine mortality was significantly less in exposed than in sham‐exposed litters, and there was a tendency (P = 0.12) for an increased incidence of malformed fetuses in exposed litters. Neither end point was significantly affected in the second experiment. Copulatory behavior of the female F1 offspring, which were bred at three months of age, was not affected in either experiment. There was a statistically significant decrease in the fertility of F1 exposed females and a significant increase in the fraction of exposed litters with malformed fetuses in the first experiment; both end points were essentially the same in the sham and exposed groups of the second experiment. That the significant effects detected in the first experiment were not seen in the second may be attributed to random or biological variation. Alternatively, the finding may indicate that the response threshold for induction of malformations lies near 100 kV/m.

Validation of Expert Judgment in Assessing Occupational Exposure to Magnetic Fields in the Utility Industry

OBJECTIVES: To investigate the reproducibility of wire codes to characterise residential power line configurations and to determine the extent to which wire codes provide a proxy measure of residential magnetic field strength in a case-control study of childhood leukaemia conducted in nine states within the United States. METHODS: Misclassification of wire codes was assessed with independent measurements by two technicians for 187 residences. The association between categories of wire code and measured level of magnetic field was evaluated in 858 residences with both a wire code measurement and a 24 hour measurement of the magnetic field in the bedroom. The strength of the association between category of wire code and risk of leukaemia was examined in two regions with different average levels of magnetic field in homes with high categories of wire code. RESULTS: The reproducibility of any of three different classifications of wire codes was excellent (kappa > or = 0.89). Mean and median magnetic fields, and the percentage of homes with high magnetic fields increased with increasing category for each of the wire code classification schemes. The size of the odds ratios for risk of leukaemia and high categories of wire code did not reflect the mean levels of the magnetic field in those categories in two study regions. CONCLUSION: Misclassification of categories of wire code is not a major source of bias in the study. Wire codes provide a proxy measure of exposure to residential magnetic fields. If magnetic fields were a risk factor for leukaemia, however, there would be some attenuation of risk estimates based on wire codes because of misclassification of exposure to magnetic fields at both extremes of the wire code range. The lack of an association between high categories of wire code and risk of leukaemia cannot be explained by a failure of the wire code classification schemes to estimate exposure to magnetic fields in the study area.