Amyotrophic lateral sclerosis and occupational exposure to electromagnetic fields.

Abstract

In an hypothesis-generating case-control study of amyotrophic lateral sclerosis, lifetime occupational histories were obtained. The patients (n = 28) were clinic based. The occupational exposure of interest in this report is electromagnetic fields (EMFs). This is the first and so far the only exposure analyzed in this study. Occupational exposure up to 2 years prior to estimated disease symptom onset was used for construction of exposure indices for cases. Controls (n = 32) were blood and nonblood relatives of cases. Occupational exposure for controls was through the same age as exposure for the corresponding cases. Twenty (71%) cases and 28 (88%) controls had at least 20 years of work experience covering the exposure period. The occupational history and task data were used to classify blindly each occupation for each subject as having high, medium/high, medium, medium/low, or low EMF exposure, based primarily on data from an earlier and unrelated study designed to obtain occupational EMF exposure information on workers in "electrical" and "nonelectrical" jobs. By using the length of time each subject spent in each occupation through the exposure period, two indices of exposure were constructed: total occupational exposure (E1) and average occupational exposure (E2). For cases and controls with at least 20 years of work experience, the odds ratio (OR) for exposure at the 75th percentile of the E1 case exposure data relative to minimum exposure was 7.5 (P < 0.02; 95% CI, 1.4-38.1) and the corresponding OR for E2 was 5.5 (P < 0.02; 95% CI, 1.3-22.5). For all cases and controls, the ORs were 2.5 (P < 0.1; 95% CI, 0.9-8.1) for E1 and 2.3 (P = 0.12; 95% CI, 0.8-6.6) for E2. This study should be considered an hypothesis-generating study. Larger studies, using incident cases and improved exposure assessment, should be undertaken.

AI evidence extraction

Main findings

Occupational EMF exposure was classified (low to high) and summarized as total (E1) and average (E2) exposure indices. Among participants with ≥20 years of work experience, odds ratios comparing the 75th percentile of case exposure (vs minimum exposure) were 7.5 for E1 (P<0.02; 95% CI 1.4–38.1) and 5.5 for E2 (P<0.02; 95% CI 1.3–22.5). In the full sample, ORs were 2.5 for E1 (P<0.1; 95% CI 0.9–8.1) and 2.3 for E2 (P=0.12; 95% CI 0.8–6.6).

Outcomes measured

• Amyotrophic lateral sclerosis (ALS) case status

Limitations

• Hypothesis-generating case-control study design
• Clinic-based cases (not incident cases)
• Small sample size (28 cases, 32 controls) with wide confidence intervals
• Controls were blood and nonblood relatives of cases (potential selection/shared-environment issues)
• Exposure assessment based on occupational classification using data from an earlier unrelated study; not direct measurements
• Exposure classification into broad categories (low to high) may cause misclassification
• Exposure window excluded the 2 years prior to estimated symptom onset

Suggested hubs

• occupational-exposure (0.95)
  Study evaluates occupational EMF exposure in relation to ALS using job-history-based exposure indices.

{
    "study_type": "case_control",
    "exposure": {
        "band": null,
        "source": "occupational",
        "frequency_mhz": null,
        "sar_wkg": null,
        "duration": "Lifetime occupational histories; exposure indices constructed through up to 2 years prior to estimated symptom onset (cases) and through same age for matched controls"
    },
    "population": "Clinic-based amyotrophic lateral sclerosis (ALS) patients and relative controls",
    "sample_size": 60,
    "outcomes": [
        "Amyotrophic lateral sclerosis (ALS) case status"
    ],
    "main_findings": "Occupational EMF exposure was classified (low to high) and summarized as total (E1) and average (E2) exposure indices. Among participants with ≥20 years of work experience, odds ratios comparing the 75th percentile of case exposure (vs minimum exposure) were 7.5 for E1 (P<0.02; 95% CI 1.4–38.1) and 5.5 for E2 (P<0.02; 95% CI 1.3–22.5). In the full sample, ORs were 2.5 for E1 (P<0.1; 95% CI 0.9–8.1) and 2.3 for E2 (P=0.12; 95% CI 0.8–6.6).",
    "effect_direction": "harm",
    "limitations": [
        "Hypothesis-generating case-control study design",
        "Clinic-based cases (not incident cases)",
        "Small sample size (28 cases, 32 controls) with wide confidence intervals",
        "Controls were blood and nonblood relatives of cases (potential selection/shared-environment issues)",
        "Exposure assessment based on occupational classification using data from an earlier unrelated study; not direct measurements",
        "Exposure classification into broad categories (low to high) may cause misclassification",
        "Exposure window excluded the 2 years prior to estimated symptom onset"
    ],
    "evidence_strength": "very_low",
    "confidence": 0.7800000000000000266453525910037569701671600341796875,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "amyotrophic lateral sclerosis",
        "ALS",
        "occupational exposure",
        "electromagnetic fields",
        "EMF",
        "case-control",
        "exposure assessment",
        "odds ratio"
    ],
    "suggested_hubs": [
        {
            "slug": "occupational-exposure",
            "weight": 0.9499999999999999555910790149937383830547332763671875,
            "reason": "Study evaluates occupational EMF exposure in relation to ALS using job-history-based exposure indices."
        }
    ]
}

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