Melatonin Levels and Low-Frequency Magnetic Fields in Humans and Rats: New Insights

2019 · Mixed · Low evidence

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MixedLow evidencePaper 1681

Study snapshot

Publicationmanual · 2019

Study typereview

Reported directionMixed

Evidence ratingLow

Abstract

Melatonin Levels and Low-Frequency Magnetic Fields in Humans and Rats: New Insights Bouché NF, McConway K. Melatonin levels and low-frequency magnetic fields in humans and rats: New insights from a Bayesian logistic regression. Bioelectromagnetics. 2019 Sep 29. doi: 10.1002/bem.22218. Abstract The present analysis revisits the impact of extremely low-frequency magnetic fields (ELF-MF) on melatonin (MLT) levels in human and rat subjects using both a parametric and non-parametric approach. In this analysis, we use 62 studies from review articles. The parametric approach consists of a Bayesian logistic regression (LR) analysis and the non-parametric approach consists of a Support Vector analysis, both of which are robust against spurious/false results. Both approaches reveal a unique well-ordered pattern, and show that human and rat studies are consistent with each other once the MF strength is restricted to cover the same range (with B ≲ 50 μT). In addition, the data reveal that chronic exposure (longer than ∼22 days) to ELF-MF appears to decrease MLT levels only when the MF strength is below a threshold of i.e., when the man-made ELF-MF intensity is below that of the static geomagnetic field. Studies reporting an association between ELF-MF and changes to MLT levels and the opposite (no association with ELF-MF) can be reconciled under a single framework. ncbi.nlm.nih.gov Conclusions From our analysis of 62 studies on the possible variations of MLT levels in humans and rats from Jahandideh et al. [2010], Touitou and Selmaoui [2012], and Halgamuge [2013], we examined the possible relationship between a dichotomous-dependent variable (corresponding to studies showing an effect or no effect on MLT excretion pattern) and independent variables such as exposure duration and magnetic field strength using a Bayesian approach and a simple LR model. We find that: * MF exposure duration is the most significant parameter in causing changes in the MLT levels both in human (Fig. 2) and rat (Fig. 4) studies, as others have reported [e.g., Selmaoui and Touitou, 1995; Kurokawa et al., 2003; Savitz, 2003; Jahandideh et al., 2010; Vanderstraeten et al., 2012]; * human and rat studies are entirely consistent with one another, but only after matching the MF strengths to similar ranges, i.e., B ≲ 50 μT; * there seems to be no dose-dependence between any change in the MLT levels with MF strengths ranging from 0.5 to 100μT as others have reported [e.g., Kato et al., 1993; Reiter, 1993; Pfluger and Minder, 1996; Halgamuge, 2013]; and * the impact of MF on the MLT levels does, however, depend on the ELF-MF strength, in the regime where ELF-MFs are weaker than (Fig. 5). Such a window effect was already discussed in Löscher et al. [1998]. In light of these results, we suggest performing additional research on rats with ELF-MF with intensities in the range from 20 nT to 20 μT, while controlling the additional factors listed earlier in the section Limitations, because epidemiological studies have indicated that adverse effects on human health become noticeable at ∼0.4 μT. But so far, very few rat studies involved ELF‐MF with intensities below 5 μT. This range 20 nT to a few μT covers the regime experienced by humans in man‐made and natural environments. Indeed, the natural variations of the geomagnetic field range from 20 nT to a few hundreds of nT [Hitchman et al., 1998]. As MF strengths > 50 μT are not found in nature, studies on rats with MF strengths > 50 μT, or mT levels, might reveal a different (likely acute effect) than the duration-dependent effect discussed here, where perhaps one of the other factors discussed earlier has become dominant.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typereview

Effect directionmixed

PopulationHumans and rats (analysis of published studies)

Sample size62

ExposureELF · Chronic exposure > ~22 days discussed; exposure duration analyzed as a predictor

Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

Re-analysis of 62 studies suggests human and rat findings are consistent when magnetic field strengths are restricted to similar ranges (B ≲ 50 μT). Chronic exposure (> ~22 days) to ELF-MF appears to decrease melatonin levels only when MF strength is below a threshold (described as below the static geomagnetic field), and reported effect vs no-effect studies may be reconcilable within this framework.

Outcomes measured

Melatonin (MLT) levels/excretion pattern

View raw extracted JSON

{
  "study_type": "review",
  "exposure": {
    "band": "ELF",
    "source": null,
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": "Chronic exposure > ~22 days discussed; exposure duration analyzed as a predictor"
  },
  "population": "Humans and rats (analysis of published studies)",
  "sample_size": 62,
  "outcomes": [
    "Melatonin (MLT) levels/excretion pattern"
  ],
  "main_findings": "Re-analysis of 62 studies suggests human and rat findings are consistent when magnetic field strengths are restricted to similar ranges (B ≲ 50 μT). Chronic exposure (> ~22 days) to ELF-MF appears to decrease melatonin levels only when MF strength is below a threshold (described as below the static geomagnetic field), and reported effect vs no-effect studies may be reconcilable within this framework.",
  "effect_direction": "mixed",
  "limitations": [],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "extremely low-frequency magnetic fields",
    "ELF-MF",
    "melatonin",
    "Bayesian logistic regression",
    "support vector analysis",
    "humans",
    "rats",
    "exposure duration",
    "magnetic field strength",
    "window effect"
  ],
  "suggested_hubs": [
    {
      "slug": "occupational-exposure",
      "weight": 0.2,
      "reason": "ELF-MF exposure levels and duration are discussed in relation to human environments, but no specific setting is stated."
    }
  ]
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1002/bem.22218
PubMed: Not supplied

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