Report on Absorption of magnesium sulfate (Epsom salts)
across the skin
Dr RH Waring
School of Biosciences, University of Birmingham. B15 2TT,
U.K. r.h.waring@bham.ac.uk
Protocol
- Clinician in charge - Dr Sarah Nuttall, Department of
Clinical Pharmacology, Medical School, University of
Birmingham
- Scientist in charge - Dr Rosemary Waring, School of
Biosciences, University of Birmingham
- Technician in charge - Mrs Liba Klovrza, School of
Biosciences, University of Birmingham
Recruitment
Subjects were recruited from the staff of the School of
Biosciences, University of Birmingham. In all, 19 subjects (10M,
9F) were recruited for the various aspects of the study. All were
in good health, and not on any current medication. No subject
smoked more than 5 cigarettes/day or drank more than 2 units of
alcohol/day. The ages ranged from 24-64 years.
Analyses
Magnesium levels in blood and urine were measured by a flame
photometric method using magnesium nitrate as a reference
standard. Sulfate was measured by anion-specific high pressure
liquid chromatography (hplc), calibrated with a turbidimetric
method and with sodium sulfate standards.
Results
After initial pilot studies, all volunteers took baths
(temperatures 50-55°C) and stayed in the bath for 12 minutes.
They added varying amounts of magnesium sulfate (Epsom salts) to
the bath before entry and ensured that the salts were completely
in solution.
Blood/Urine Samples
Blood samples were taken before the first bath, at 2h after
the first bath and at 2h after the 7th consecutive bath. Baths
were taken daily at the same time for 7 days for the experiment.
Urine samples were collected before the first bath and then 2h
after the first bath and at all subsequent baths . Urine samples
were also taken 24h after the last bath. All urine samples were
corrected for creatinine content.
Results
Magnesium
Magnesium levels in blood are very tightly controlled. Of 19
subjects, all except 3 showed a rise in magnesium concentrations
in plasma, though this was small in some cases. The values before
the first bath were, mean 104.68 ± 20.76 ppm/ml; after the
first bath the mean was 114.08 ± 25.83 ppm/ml.
Continuation of bathing for 7 days in all except 2 individuals
gave a rise to a mean of 140.98 ± 17.00ppm/ml. Prolonged
soaking in Epsom salts therefore increases blood magnesium
concentrations. Measurement of magnesium levels in urine showed a
rise from the control level, mean 94.81 ± 44.26 ppm/ml to
198.93 ± 97.52 ppm/ml after the first bath. Those
individuals where the blood magnesium levels were not increased
had correspondingly large increases in urinary magnesium showing
that the magnesium ions had crossed the skin barrier and had been
excreted via the kidney, presumably because the blood levels were
already optimal. Generally, urinary magnesium levels 24h after
the first bath fell from the initial values found after day 1
(mean 118. 43 ± 51.95) suggesting some retention of
magnesium in tissues after bathing as blood levels were still
high.Measurement of magnesium levels in urine 24h after the 7th
bath gave values almost back to control levels.
Sulfate
Free inorganic sulfate levels in plasma rose in all subjects
after bathing in Epsom salts (mean pre-bath, 3.28 nmol/mg protein
± 1.40, 2h after 1st bath, mean 5.59 nmol/mg protein
± 3.08). In some individuals, the level post-bath reached
> 9 nmol/mg protein. The plasma levels after 7 days showed a
mean of 3.57 nmol/mg protein ± 1.70, lower than the peak
value, suggesting that sulfate stores in the body were being
filled. Analysis of the urine samples again showed an increase in
sulfate concentrations (pre-bath mean 623.74 ± 352.34
nmols/ml, 2h post bath 1093.30 ± 388.79 nmoles/ml, 24h
after 1st bath 899.83 ± 483.16 nmols/ml. Sulfate excretion
in urine in some individuals was only slightly higher after 7
days bathing than the pre-bath levels.
Other Factors
Gender Differences
Males had slightly higher levels of blood magnesium than
females (109.0 ± 14.4 ppm/ml v. 87.7 ± 6.3 ppm/ml.
Females had higher free plasma sulfate than males (3.26 ±
0.86 nmol/mg. v. 2.54 ± 0.53 nmol/ug) although these
differences were not significant. The mean levels of both
magnesium and sulfate were almost identical for males and females
after bathing.
Optimum Epsom Salt Levels
There was a wide individual variation in this parameter.
However, all individuals had significant rises in plasma
magnesium and sulfate at a level of 1% Epsom salts .This equates
to 1g MgS04/100ml water; 600g Epsom salts/60 litres, the standard
size UK bath taken in this project (~15 US gallons). However,
most volunteers had significantly raised Mg/S04 levels on baths
with 400g MgS04 added. Above the 600g/bath level, volunteers
complained that the water felt 'soapy'. Although this project did
not specifically set out to answer the question of how frequently
baths should be taken, the results are consistent with saturation
of the skin (and possibly the gut ) transporters .These proteins
are not well understood or described but, at least for sulfate,
they are believed to be high affinity but low capacity.The values
obtained suggest that most people would find maximal benefit by
bathing 2 or 3 times/ week, using 500-600g Epsom salts each
time.
Other factors
No volunteer complained of any adverse effects, even at MgSO4
levels of 2.5%. Possible effects on the kidneys were tested by
measuring urinary protein content. This did not change
significantly, whichever Epsom salt levels were used, over the
8-day period. Kidney damage is therefore not an issue. In other
experiments using excised human skin, we found that sulfate does
penetrate across the skin barrier. This is quite rapid so
probably involves a sulfate transporter protein. We did not see
any Mg penetration, but these experiments were conducted for a
short time at only 37 degrees as opposed to the 50 degree bath
temperature.To check this, 2 volunteers wore 'patches' where
solid MgSO4 was applied directly to the skin and sealed with a
waterproof plaster. Plasma/urine analysis confirmed that both Mg
and sulfate levels had increased so this is potentially a
valuable way of ensuring Epsom salts dosage if bathing is not
available. Interestingly, both volunteers, who were > 60 years
old, commented without prompting that 'rheumatic' pains had
disappeared.
Conclusion
Bathing in Epsom salts is a safe and easy way to increase
sulfate and magnesium levels in the body.
This page was first uploaded to The Magnesium Web Site on
January 10, 2004
http://www.mgwater.com/
Healthy Water
Association--USA