Nocturnal leg cramps (NLC) are painful, involuntary contractions of muscles occurring at rest, mostly at night. A Cochrane review on leg cramps in pregnancy showed some potential benefits in trials of magnesium. This is a single center, prospective, randomized, double blind, placebo controlled clinical trial that aims to investigate the effect of treatment with Magnox 520® (un-organic granular magnesium complex, composed of Magnesium Oxide & Magnesium Oxide Monohydrate 865mg, Provides 520 mg of free elemental Mg++) on frequency and severity of NLC, quality of sleep and quality of life. Hypothesis: Magnox 520® may reduce the number and severity of NLC; an improvement in the quality of life and quality of sleep may ensue.