Why This Study Gets Cited Constantly — and Rarely Read Carefully
If you've spent any time reading about grounding and sleep, you've almost certainly encountered a reference to the Ghaly and Teplitz study. It's the single most cited piece of research in the grounding and sleep literature, reproduced across brand product pages, wellness blogs, and grounding documentaries with varying degrees of accuracy and almost universal omission of the methodological details that make its findings credible in some ways and limited in others.
GroundingMatrix covers this study in our Science Index — where we list it with its full citation, DOI, and an honest evidence quality rating. What we haven't done until this post is read it carefully in public and explain specifically what it measured, how it measured it, what the numbers actually showed, and where the evidence the study produced ends and where interpretation and extrapolation begin.
That distinction matters for buyers. If a grounding sheet product page cites this study as evidence that grounding "improves sleep quality and reduces pain and stress," it's telling you something true in the general direction but omitting the sample size, the study design, and the specific outcome variables that tell you how confident to actually be in those claims and for what population they're most likely to apply. GroundingMatrix's job is to give you those details rather than the headline.
The Study — Full Citation and Basic Context
The study is: Ghaly M, Teplitz D. "The biologic effects of grounding the human body during sleep as measured by cortisol levels and subjective reporting of sleep, pain, and stress." Journal of Alternative and Complementary Medicine. 2004;10(5):767-776. DOI: 10.1089/acm.2004.10.767. PubMed ID: 15650465.
Published in 2004 in the Journal of Alternative and Complementary Medicine — a peer-reviewed journal, PubMed indexed, with standard editorial review. The authors are Maurice Ghaly, a physician, and Dale Teplitz, a wellness practitioner. Clint Ober — the grounding pioneer whose research history GroundingMatrix covers on the Earthing.com brand page — is credited in the paper as the originator of the grounding method being studied.
This context matters: the study was conducted within Clint Ober's research programme, which means it carries the credibility of peer review and the limitation of not being conducted by a fully independent research team with no connection to grounding's commercial development. GroundingMatrix considers this a relevant nuance rather than a dealbreaker — it's common for foundational research in emerging fields to be conducted by people connected to those fields — but it's worth knowing before accepting the findings as equivalent in independence to research funded by entirely neutral parties.
The Study Design — What Was Actually Done
Understanding the study design is the most important step in evaluating what the findings mean. Here's what the researchers actually did, as precisely as GroundingMatrix can summarise from the published paper.
Subjects: 12 participants — 6 men and 6 women — described as having sleep disturbances, pain, and stress. The paper doesn't report a formal clinical diagnosis for these conditions; the subjects self-reported these issues before enrolment. This is an important detail: 12 subjects is a small sample by clinical research standards. The statistical conclusions that can be drawn from 12 people are inherently limited compared to what could be drawn from 120 or 1,200 people.
Design: The study used a crossover design — each subject served as their own control, sleeping grounded for a period and ungrounded for a period, with measurements taken in both conditions. A crossover design is a strength in small-sample research because it removes between-subject variability: instead of comparing 6 grounded people to 6 ungrounded people (where individual differences confound the results), each person is compared to their own baseline, which is a statistically cleaner comparison.
Duration: 8 weeks of grounding, compared to a control period. The 8-week timeframe is meaningful and reflects genuine understanding of the grounding mechanism's cumulative nature — the researchers weren't looking for overnight effects, which is consistent with what GroundingMatrix covers in our routine building guide about realistic timelines.
Grounding method: Subjects slept on conductive carbon-based pads connected to outdoor ground rods — a direct earth connection rather than an outlet-based connection. This is the most unambiguous grounding method available for research purposes, since it bypasses any question about whether specific wall outlet grounding is functioning correctly and establishes a verifiable direct earth connection for the study period.
Blinding: The study was not double-blind. Participants knew whether they were grounded or ungrounded. This is a limitation that the authors acknowledge — subjects' awareness of their grounding status could influence subjective reports, which is the standard placebo concern in wellness research. The objective cortisol measurements are less vulnerable to this concern than the subjective sleep, pain, and stress ratings, which is part of why GroundingMatrix weights the cortisol data more heavily than the subjective reports when assessing this study's contribution to the grounding evidence base.
What Was Measured — The Objective Outcome Variable
The study measured two categories of outcomes. The objective category — the one GroundingMatrix considers most significant — is 24-hour salivary cortisol profiles.
Cortisol was measured from saliva samples collected at six time points across 24 hours: midnight, 8am, noon, 4pm, 8pm, and midnight again. These six measurements across a full day allowed the researchers to chart the full diurnal cortisol rhythm — how cortisol rises and falls through the day and night — rather than taking a single snapshot that might miss the rhythm's shape.
This is a methodologically thoughtful measurement approach. A single cortisol measurement — morning or evening — tells you the level at that moment but nothing about the rhythm's shape. The full diurnal profile tells you whether the rhythm is following the healthy arc (low at night, peak 30-45 minutes after waking, declining through the afternoon and evening) or whether it's disrupted in ways that affect both sleep onset and the body's ability to maintain deep sleep through the night.
What the cortisol data showed: subjects' diurnal cortisol profiles became more consistent with the healthy pattern during grounded sleep compared to ungrounded periods. Specifically — and this is the detail most frequently omitted in marketing citations of this study — the effect was more pronounced in female subjects than in male subjects. GroundingMatrix considers this sex-differentiated finding worth flagging because it suggests the cortisol normalisation effect may not apply equally across all demographics, which is exactly the kind of nuance that "grounding normalises cortisol" as a universal claim doesn't capture.
What Was Measured — The Subjective Outcome Variables
The second category of outcomes was subjective self-report: participants reported on their sleep quality, pain levels, and stress levels during grounded and ungrounded periods using standardised questionnaires and visual analogue scales.
The findings on subjective outcomes were positive across the board. 11 of 12 subjects reported falling asleep faster during the grounded period. All 12 reported fewer nighttime wake-ups. The majority reported reduced pain and stress scores during grounding compared to the ungrounded control period.
These are striking findings — 12 out of 12 reporting fewer nighttime wake-ups is a strong directional signal. But the subjective nature of these measurements requires honest qualification. Subjects knew which condition they were in (grounded or ungrounded). The expectation that grounding would help may have influenced how they perceived and reported their sleep, pain, and stress. This is the placebo concern that's standard in wellness research and that the absence of blinding in this study cannot rule out.
GroundingMatrix's position: the subjective findings are consistent with the objective cortisol data and with the broader grounding literature, which makes them more credible than isolated subjective reports without any objective corroboration. But they cannot be read with the same confidence as the cortisol measurements, which don't respond to expectation effects the way subjective ratings do. Both types of data belong in an honest account of what this study found — with the appropriate weighting applied to each.
The Cortisol Finding in More Detail — What "Normalisation" Actually Means
Because the cortisol finding is the most significant and most frequently cited, GroundingMatrix wants to explain specifically what "cortisol rhythm normalisation" means in the context of this study — because "normalised cortisol" gets used as a shorthand that obscures what was actually observed.
The healthy diurnal cortisol pattern looks like this: lowest levels during the first half of the night (the deep sleep window), a sharp rise beginning about 30-45 minutes before waking (the cortisol awakening response that drives alert morning arousal), a sustained high level through the morning, a gradual decline through the afternoon, and a further decline through the evening toward the nighttime low. The overall shape is a pronounced curve — very low at night, high in the morning, declining through the day.
In people with disrupted circadian rhythm, chronic stress, or autonomic dysregulation — the profile of subjects in this study — this curve is flattened, shifted, or inverted. Evening cortisol stays elevated when it should be declining, making sleep onset difficult. Morning peaks are blunted when they should be sharp, leaving people feeling flat rather than alert on waking. The low during the first half of the night may not be as low as it should be, disrupting the hormonal environment in which deep sleep is meant to occur.
What the study found was that during the grounded sleep period, subjects' cortisol profiles showed movement toward the healthy curve — more pronounced nighttime lows, more appropriately timed morning peaks, better overall rhythm shape compared to their ungrounded periods. Not a return to a perfect healthy baseline in all cases, but a measurable movement in the right direction, documented across six measurement points across 24 hours rather than inferred from a single reading.
This is what "cortisol normalisation" means in the context of this study. It's a specific, objective, multi-point measurement finding — not a vague wellness claim. The mechanism GroundingMatrix considers most plausible for producing this finding is the parasympathetic nervous system shift that grounding research has documented more broadly — a shift toward the rest-and-digest state during sleep contact that creates the autonomic conditions under which the cortisol rhythm can re-establish its natural timing.
What the Study Didn't Measure — The Honest Gaps
GroundingMatrix considers what a study doesn't measure as important as what it does — because what's absent from a study determines where its conclusions can't legitimately be extended, regardless of how marketing citations frame it.
It didn't measure sleep architecture objectively. The study's sleep quality data came from self-report rather than polysomnography — the objective brain-wave and physiological measurement that directly characterises sleep stages. GroundingMatrix covers polysomnography in our glossary specifically as the gold standard for sleep research. Without it, "improved sleep quality" in this study means "subjects reported their sleep felt better" — which is meaningful but not the same as "subjects spent more time in slow-wave deep sleep" or "subjects showed improved sleep architecture." The distinction matters for confidence.
It didn't study a general healthy population. Subjects were specifically recruited for having sleep disturbances, pain, and stress. The findings are most directly applicable to people in similar states — not to athletes optimising already-good sleep, or to people without significant baseline disruption. Extrapolating from this study to universal sleep improvement claims for all grounding users goes beyond what the subject selection supports.
It didn't study different grounding formats. The study used ground-rod-connected carbon pads. Whether outlet-based grounding through a wall socket produces equivalent cortisol effects — which is how nearly every commercial earthing sheet works — is an inference from the mechanism rather than a finding of this specific study. GroundingMatrix considers this a reasonable inference given the mechanism's equivalence, but it's worth being precise that the study's direct findings are about direct earth connection rather than outlet-mediated connection.
It didn't measure inflammatory markers. Given the overlap between cortisol dysregulation and chronic inflammation — both driven by sympathetic nervous system overactivation and both relevant to sleep disruption — measuring inflammatory biomarkers alongside cortisol would have strengthened the study considerably. The study doesn't include this data, which means the inflammation connection present in other grounding research can't be directly drawn from the Ghaly and Teplitz findings alone.
It didn't include a placebo control. A sham grounding condition — where subjects believed they were grounded but weren't — would have isolated the grounding effect from the expectation effect in subjective outcomes. Without this, the subjective data remains susceptible to the interpretation that subjects felt better partly because they expected to. The objective cortisol data is less vulnerable to this concern but the study's inability to definitively rule out placebo contribution to the subjective outcomes is a real limitation.
How This Study Fits Into the Broader Grounding Literature
One study, however carefully designed and honestly reported, proves very little on its own. Where the Ghaly and Teplitz study earns its prominence in the grounding literature is not through its individual power — 12 subjects is too small for strong population-level conclusions — but through its role as the foundational documented exploration of a mechanism that subsequent studies have corroborated from different angles.
The Chevalier et al. 2012 comprehensive review in the Journal of Environmental and Public Health — covered in the GroundingMatrix Science Index — consolidates findings across multiple independent grounding studies on inflammation, cortisol, autonomic function, and cardiovascular markers. The direction of effect across these different studies, using different measurement approaches, different subject populations, and different outcome variables, consistently points in the same direction as Ghaly and Teplitz. That consistency of direction across independent studies is more meaningful than any single study's findings, and it's the basis on which GroundingMatrix considers the grounding and sleep literature to be encouraging rather than merely preliminary.
The Park et al. 2025 randomised controlled trial in Advances in Integrative Medicine — with 60 participants, placebo control, and double-blind design — represents the methodological advancement the field needs and the kind of research GroundingMatrix's honest science communication has been noting as necessary to upgrade "encouraging preliminary findings" to "well-established evidence." Its findings on sleep quality improvements through grounding are consistent with what Ghaly and Teplitz documented twenty years earlier, now in a more rigorous design. That consistency over two decades of research from different teams with different methods is the most meaningful signal in the entire grounding literature.
What This Means for Buyers Reading Grounding Sheet Product Pages
When a grounding sheet product page cites this study — or cites "20+ peer-reviewed studies showing grounding improves sleep" — here's how GroundingMatrix would encourage you to read that citation:
The research is real. The journal is legitimate. The cortisol findings are objective measurements rather than self-report. The direction of effect is consistent with a plausible, documented biological mechanism. The study's limitations — small sample, no blinding, self-reported primary outcomes — are real but typical of foundational research in emerging fields and don't invalidate its contribution. The subsequent research that has followed is directionally consistent.
What the research doesn't support is absolute certainty that a specific grounding sheet product will produce measurably improved sleep for every buyer within a predictable timeframe. The study was conducted on a specific population with specific baseline conditions. The grounding method was direct earth connection rather than outlet-mediated. The sample was 12 people. These details exist in the original paper and are worth knowing when a product page presents the research as universal proof of guaranteed sleep improvement.
GroundingMatrix's honest framing: the Ghaly and Teplitz study provides genuine, objective, peer-reviewed evidence that grounding during sleep produces measurable cortisol rhythm normalisation in people with disrupted sleep, pain, and stress — accompanied by consistent subjective improvements in sleep, pain, and stress ratings in the same subjects. That's a meaningful contribution to the evidence base. It supports trying a grounding sheet as a sleep intervention with realistic expectations and an adequate trial period. It doesn't guarantee your specific outcome, and no honest reading of a 12-person study should.
Which Products GroundingMatrix Recommends If This Research Resonates With You
If the cortisol rhythm and sleep architecture mechanism covered in this study is specifically what interests you — and you want a grounding sheet format that most directly addresses the sleep window the study examined — the relevant products in the GroundingMatrix index are those designed for overnight sleep grounding with full mattress or full-body coverage.
The Earthing.com Mattress Cover uses the same carbon-based material class as the ground-rod-connected carbon pads used in the Ghaly and Teplitz study — the most direct material connection between the research protocol and a commercially available product. The Premium Grounding Queen Sheet uses 30% surgical-grade stainless steel fibre — the highest Matrix Trust Score in the sheet category for material durability and transparency. The Rowland Organic Earthing Sheet is the organically certified European option. The BareEarth Grounding Bed Sheets offer the longest guarantee window at 90 days — the most generous evaluation period available for testing whether the cortisol and sleep findings translate to your specific situation.
Compare them directly on the GroundingMatrix Comparison Tool. And read the full context on what to look for and what to avoid in our grounding sheet buying guide before making a final decision.
This post reflects GroundingMatrix's independent editorial assessment of published peer-reviewed research. We are not manufacturers, researchers, or affiliated with any grounding brand. We may earn a small commission if you purchase through our links — at no extra cost to you. This content is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional before making changes to your health or wellness routine.