Magnesium

The most cited trial randomised 46 older adults with primary insomnia to 500 mg of elemental magnesium or placebo daily for 8 weeks in a double-blind design. Compared with placebo, magnesium lowered the Insomnia Severity Index score (P = 0.006), raised sleep efficiency (P = 0.03) and shortened sleep onset latency (P = 0.02), while total sleep time did not differ significantly (P = 0.37) and the reduction in early morning awakening was of borderline significance (P = 0.08) [1]. A 2021 systematic review and meta-analysis found 3 randomised trials comparing oral magnesium with placebo in 151 older adults in three countries. Pooled, magnesium shortened sleep onset latency by 17.36 minutes (95% CI 7.44 to 27.27); total sleep time was 16.06 minutes longer, a difference that was not statistically significant [2].

All trials in the 2021 review were at moderate to high risk of bias, and the authors graded the outcomes as low to very low quality of evidence, concluding that the literature was too weak for well-informed recommendations [2]. The main trial was small, enrolled only older adults, and measured sleep with questionnaires and a sleep log rather than polysomnography [1]. Effects in younger adults with adequate magnesium intake have not been tested in these trials. The main trial used magnesium oxide; claims made for other salts, such as better absorption for glycinate or better brain entry for threonate, have no comparative sleep trials among the studies cited here. Glycinate also supplies glycine, which has been studied for sleep on its own.

The 2012 trial gave 500 mg of elemental magnesium a day for 8 weeks, as two magnesium oxide tablets each containing 250 mg of elemental magnesium [1].