Randomised trial, 2002
How well does magnesium supplementation reduce premenstrual symptoms?
Unexpectedly, the placebo (sorbitol) worked better than magnesium at any dose. Sorbitol reduced anxiety-related and total symptoms more than all three magnesium doses, suggesting sorbitol itself has an effect specific to women with PMS.
What they did
85 women with premenstrual symptoms took one of four daily treatments in random order: magnesium at 200, 350, or 500 mg, or sorbitol placebo at 1305 mg. Each treatment lasted 2 months, with a 1-month break between treatments in a double-blind crossover study.
What they found
Sorbitol unexpectedly reduced anxiety-related and total premenstrual symptoms more than all three magnesium doses after 2 months (P<0.001 for both). Sorbitol also reduced urinary magnesium excretion compared to baseline and magnesium treatments (P=0.005). When 17 healthy volunteers received sorbitol, it had no effect on urinary magnesium or mood.
What it means for you
This surprising finding shows that placebo is not always inert. Sorbitol appears to affect how the body handles magnesium specifically in women with PMS, not in healthy women. This challenges assumptions about placebos in research and raises questions about how to choose them.
85 women
sample size
1305 mg
sorbitol dose
2 months
per treatment
About the study
- Original title
- Unexpected benefit of sorbitol placebo in Mg intervention study of premenstrual symptoms: implications for choice of placebo in RCTs
- Authors
- Walker AF, De Souza MC, Marakis G et al.
- Journal
- Medical hypotheses
- Year
- 2002
- Study design
- Randomised trial
- Participants
- 85
- What was tested
- Magnesium (200, 350, or 500 mg daily) or sorbitol placebo (1305 mg daily)
- Read the paper
- doi.org/10.1054/mehy.2001.1407
Topics
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