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How much magnesium increase in blood/urine after Epsom salt baths in 2017 study?
Executive summary
A small University of Birmingham pilot (19 people) reported mean plasma magnesium rising from 104.68 ± 20.76 ppm/mL before bathing to 114.08 ± 25.83 ppm/mL after one 12‑minute Epsom‑salt bath, and to 140.98 ± 17.00 ppm/mL after daily baths for seven days (all except two participants) [1]. Urinary magnesium rose initially then largely returned toward baseline 24 hours after the seventh bath, per the same report [1].
1. What the 2017/University of Birmingham report actually measured
The frequently cited University of Birmingham work (often referenced online and summarized in review articles) tested 19 volunteers who took 12‑minute whole‑body baths in hot water with magnesium sulfate; the study reported a mean plasma magnesium of 104.68 ± 20.76 ppm/mL at baseline, 114.08 ± 25.83 ppm/mL after the first bath, and 140.98 ± 17.00 ppm/mL after seven days of bathing in all but two participants [1]. The report also noted rises in plasma sulfate and a urinary magnesium pattern that peaked early then “almost” returned to control values 24 hours after the seventh bath [1].
2. How other outlets describe the same numbers
ConsumerLab summarized this preliminary evidence by saying Epsom salts in a bath “can raise magnesium levels in the body” and links readers to that study for details [2]. GrassrootsHealth likewise relayed that 17 of 19 participants showed elevated serum magnesium after a week of baths, while the remaining two showed higher urinary magnesium—taken as evidence the mineral crossed the skin [3]. Multiple blogs, wellness sites and vendors repeat the Birmingham figures and translate concentration data into practical doses (grams per bath) without adding new peer‑reviewed verification [4] [5].
3. Important methodological and publication limitations
The University of Birmingham dataset behind these numbers appears only on the web and not in a peer‑reviewed journal; a critical review in PubMed Central flagged the study’s “questionable quality” for proving transdermal magnesium absorption and emphasized it wasn’t peer‑reviewed [1]. That review concluded that claims of effective transdermal magnesium are scientifically unsupported, even while quoting the reported plasma/urine changes [1].
4. What the magnitude of the change means — put in context
Reported means move from ~104.7 to ~141 ppm/mL after a week, a roughly 35% increase in the cited units in that dataset, but the review and summaries emphasize the changes were small in some participants and highly variable across individuals [1]. Urine data showed an early rise then a near‑return to baseline 24 hours after the last bath, suggesting transient redistribution rather than a large, sustained systemic loading [1].
5. Conflicting expert takes and mainstream reporting
National Geographic and other mainstream outlets report skepticism from experts who emphasize human skin as a barrier and say it’s “unlikely you can absorb much magnesium through your skin,” citing broader scientific opinion that questions substantial transdermal uptake despite the Birmingham report [6]. In contrast, industry groups and health blogs use the Birmingham numbers to argue baths can meaningfully boost magnesium—an interpretation the academic review explicitly questions [7] [3] [4].
6. Practical takeaways and unanswered questions
Available reporting shows one small, non‑peer‑reviewed study reported measurable rises in plasma magnesium after repeated Epsom‑salt baths and transient urinary changes [1]. However, authoritative reviews flag study quality concerns and broader literature reviews conclude evidence for reliable, clinically meaningful transdermal magnesium absorption remains weak or unsupported [1] [6]. Important unanswered questions—such as reproducibility, dose–response, longer‑term retention, clinical outcomes and standardized measurement units across labs—are not resolved in current reporting [1].
7. How to read future claims and what to watch for
When you see claims quoting the Birmingham figures, check whether the source acknowledges the study’s limited publication status and the critical review that disputes broad conclusions [1]. Peer‑reviewed replications measuring plasma/urine magnesium with clear units, standardized baths, blinded protocols and clinical outcomes would be the decisive evidence not yet present in the available reporting [1] [6].
Limitations: this analysis uses only the provided search results and cites them directly; additional peer‑reviewed trials or datasets beyond these sources were not found in the current reporting [1] [2] [6].