Science and Research

A note on reading these

The studies summarised here differ considerably in scale and in how much they can tell us. Alongside a controlled permeation study there are pilot studies with small numbers of participants and feasibility studies without a control group. We report them as they were published — they describe the state of the research, not the effect of any product.

Shealy: the first evidence of uptake

The earliest investigations into transdermal magnesium absorption come from the American physician Norman Shealy. Over six years he examined various transdermal preparations, measuring intracellular magnesium levels. He reports that a magnesium deficiency could be corrected under transdermal application within four to six weeks. For comparison he gives two weeks for intravenous administration and six to twelve months for oral supplementation. The ratio of calcium to magnesium also shifted towards magnesium (1).

Watkins and Josling: a pilot study using hair analysis

In a pilot study, both blood levels and cellular magnesium content were measured by hair analysis before and after twelve weeks of transdermal application of a 31 per cent saturated magnesium chloride solution.

In 89 per cent of participants, cellular magnesium content had risen by an average of 59.5 per cent after twelve weeks. The calcium-to-magnesium ratio improved by an average of 25.2 per cent. The authors additionally report indications of increased heavy-metal excretion in 78 per cent of participants (2).

For context: this is a pilot study without a control group. Hair analysis as a method for determining magnesium status is not uncontested in the field.

Waring, University of Birmingham: uptake from a full bath

At the University of Birmingham, researchers examined whether magnesium is taken up from a full bath. Nineteen people bathed for twelve minutes a day over seven days in a one per cent magnesium sulfate solution. Magnesium content was measured in blood and urine.

In 16 of the 19 participants, magnesium levels in both blood and urine rose steadily over the period. In those whose blood levels did not rise, a marked increase was measured in urine. The author concludes that magnesium is taken up from a bath through the skin and, depending on the individual’s magnesium status, excreted again via the kidneys (3).

Mayo Clinic: a feasibility study

A feasibility study on transdermally applied magnesium was conducted at the Mayo Clinic in Rochester. Participants were 40 women with a diagnosis of fibromyalgia; symptoms were recorded by questionnaire at baseline and after two and four weeks. Four sprays were applied to arms and legs twice daily over four weeks. Twenty-four participants completed the study, and the recorded scores improved over the study period (4).

For context: this is a feasibility study — it tests whether a study design is workable. There was no control group and no blinding, and 16 of the 40 participants dropped out. No evidence of efficacy can be derived from it.

Chandrasekaran and Barnard, University of Queensland: the route through the skin

Published in 2016, the work from the University of Queensland in Brisbane, led by Prof. Ross Barnard, examined the permeation of topically applied magnesium ions through human skin. The finding: magnesium does cross the skin, predominantly via the hair follicles. The extent depends on the concentration of the solution and on contact time (5).

Of the studies listed here, this is the most methodologically robust on the question of whether magnesium crosses the skin. It makes no claim about clinical effects.

What follows from this — and what does not

Taken together, these studies support the assumption that magnesium is absorbed through the skin and that hair follicles are the principal route. On the extent of that absorption, on how it compares with oral intake, and on clinical effects, the data are thin: small numbers of participants, mostly no control groups, and in places methods that are open to challenge.

Robust controlled trials on clinical endpoints are so far lacking. Anyone who needs an answer about their own nutritional status will not find it in this overview, but in a conversation with a qualified healthcare professional.