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I've heard this claim several times from family members, and I was highly skeptical. Supposedly the mere presence of a bar of soap underneath the mattress can ward off leg cramps during the night. The brand of soap does not appear to matter.

I assumed that this was just an urban legend, yet Snopes.com indicates that this is "undetermined".

Have there been any studies on this phenomena? My first thought is "placebo effect" (actually, that was my second thought; my first thought was far less polite). Have any double-blind studies been performed to test this, or are there any theories that could explain why this might be effective (beyond the placebo effect)? I find Snopes' speculation that "perhaps soap releases something into the air that is beneficial" not very credible.

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If the bar of soap creates a lump in your mattress under your back, then the pain your back will probably make the leg cramps unnoticeable. ;-D –  Randolf Richardson Aug 3 '11 at 17:11
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@Randolf - actually, having something raised below the back might sometimes HELP with back pain (from practical experience) –  DVK Aug 3 '11 at 18:13
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Here's the problem: Real research costs time and money. Claims in the "you gotta be kidding me" category often don't get investigated. The thing with the soap is: There isn't even a plausible mechanism for it –  Lagerbaer Aug 3 '11 at 19:36
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"Theories that could explain it" -> That wouldn't be a theory but a hypothesis. –  Lagerbaer Aug 3 '11 at 20:05
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@jwenting the claims are that no specific brand is necessary. I have added that to the question. My personal (skeptical) belief is placebo. The snopes article, as I mentioned, suggests some airborne chemical common to all (most) bar soaps. In the absence of research or theories that would fit, it may very well be the answer is "probably placebo," but it would be nice to replace that "probably" with a "definitely". –  Beofett Aug 4 '11 at 12:18
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2 Answers 2

up vote 6 down vote accepted

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.

TL;DR Conclusion

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.

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did any studies mention what was used as a placebo? My gut instinct was that having a "brick" under the mattress is what helps, not the soap –  Andrey Aug 4 '11 at 18:07
    
Snopes was weighed in on the subject suggesting its status is "undetermined". They go onto say "Yet skepticism aside, for those subject to nocturnal leg cramps, this bit of folk wisdom is clearly worth a try, in that the only potential downside is their having to share their beds with slivers of soap." Did Snopes just say "skepticism aside"? Colour me surprised. –  Oddthinking Aug 23 '11 at 3:28
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Yon Doo Ough, Russell Albert, David D. Bhaskar, G. Thomas Jones and KeriLynn Loftus. The Journal of Alternative and Complementary Medicine. July 2008, 14(6): 618-618. doi:10.1089/acm.2007.0819.

This is a brief trial on 11 patients with severe menstrual cramps aged 21 - 48 years using crushed soap with application via a patch and reported a positive result. The number of patients is quite limited and it was not a double blind study.

Yon Doo Ough went on to perform a further study after these positive results on 83 patients with Fibromyalgia.

All patients reported initial pain relief within one hour of application, including one patient who reported nearly immediate relief within three minutes. Three patients reported nearly complete relief of pain (rated 0–3), and the remainder reported pain levels of 4 or less. The pain relief lasted between 18 hours to 30 hours. Many patients also reported that nighttime application of the SSO skin patch gave the added benefit of more restful sleep.

There also appears to be a related patent http://www.boliven.com/patent/US20060182818. Note: I know nothing about patents, this may not be a true patent, just something related I found.

Both of these studies are limited and are not double blind studies. The studies do indicate that patients personally indicated there was significant relief associated with these soap patches.

The wording in the studies is also a bit iffy, so I would take it more along the lines of strong anecdotal evidence than a conclusive study. It's a very interesting precursor for prompting a serious double blind study which appears to have not been done so far.

The cause of the relief in both studies is put down to the scent having a relaxing effect. This leads to another skeptical question: how effective is aromatherapy outside of the placebo effect?

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Related question, by the same author, triggered by this answer: skeptics.stackexchange.com/questions/5602/… –  Oddthinking May 17 '12 at 0:17
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