Is there evidence for soap helping with cramps?
I searched for treatments of nocturnal leg cramps.
I found lots of anecdotal claims about the soap remedy, confirming it is a notable claim, but no studies despite there being literature reviews and meta-analyses out there..
Most of the treatments were for stretching, or ingesting drugs such as quinine, magnesium, vitamin B, vitamin E and other drugs.
I note that Vitamin E is the ingredient of some soaps, but I do not believe it is volatile (a relatively large molecule with a 205°C boiling point) and there is no way someone could inhale, through a mattress, the dosages tested (400-800 IU is about 260-800mg, depending on the type of Vitamin E)
Is it just Placebo Response?
So, I set out to see if there was any evidence that nocturnal leg cramps responded well to placebo treatments. If they did, we could more easily dismiss the soap-user's anecdotes as the placebo effect.
I found somewhat mixed results:
- I found some weak evidence for a strong placebo effect in:
Placebo-controlled trial of quinine therapy for nocturnal leg cramps.
M C Fung and J H Holbrook, West J Med. 1989 July; 151(1): 42–44. PMCID: PMC1026949
Although all patients claimed to have an average of at least two cramps per week before the trial, three patients had fewer than eight cramps during the four weeks when they were receiving a placebo.
The data shows a small number of participants had only small drops from the baseline (e.g. 5 or 6 instead of 8 expected) over a short period (4 weeks). Given the initial data was what the patients claimed, rather than measured, this seemed to be insignificant.
- I found some evidence against a strong placebo effect in:
Randomized, double-blind, placebo-controlled study of the safety and efficacy of vitamin B complex in the treatment of nocturnal leg cramps in elderly patients with hypertension. Chan P, Huang TY, Chen YJ, Huang WP, Liu YC SOJ Clin Pharmacol. 1998;38(12):1151
those taking placebo had no significant difference from baseline.
I found some good evidence for a strong placebo effect:
Magnesium for the Treatment of Nocturnal Leg Cramps A Crossover Randomized Trial, Ricardo Frusso, Miguel Zárate, Federico Augustovski, Adolfo Rubinstein, Journal of Family Practice. November 1999 · Vol. 48, No. 11
We observed a significant period-effect bias: All patients improved over time regardless of the treatment sequence they received. [...] The period-effect bias probably occurred because of a combination of the natural history of this condition, a regression to the mean, and a true placebo effect.
I found more good evidence for a strong placebo effect:
Effectiveness of quinine in treating muscle cramps: a double-blind, placebo-controlled, parallel-group, multicentre trial. Diener HC, Dethlefsen U, Dethlefsen-Gruber S, Verbeek P., Int J Clin Pract. 2002 May;56(4):243-6. PMID: 12074203
26 (53%) [of participants] in the placebo group had a reduction of at least 50% in the number of muscle cramps. [...] The improvement [due to treatment] was more evident according to physician assessment than patient assessment; this is corroborated by the high placebo response rate.
No soap studies, even in broad literature reviews and meta-analysis. Several drugs have real effects. Attributing the soap claims to placebo is plausible, as some (but not all) studies show a high placebo response.