Actor Scarlett Johansson has reportedly stated she takes magnesium to improve her digestion and sleep, a claim that has led to a surge of public inquiries to dietitians. Johansson reportedly told beauty publication Byrdie, “I know that everybody is taking magnesium now. It’s so helpful.”
However, health experts are urging caution, noting that the scientific evidence for broad benefits from magnesium supplementation is inconsistent. Dietitian Danielle Shine explained that while magnesium is an essential mineral for functions like blood pressure regulation and bone health, deficiency is not common in Australia.
Shine also highlighted that studies on magnesium's effect on sleep are generally small and short-term, making it difficult to draw firm conclusions. Similarly, there is no strong evidence that magnesium supplementation provides broad benefits for nervous system function, exercise recovery, or preventing muscle cramps.
Some forms of supplemental magnesium can have a laxative effect, and sports dietitian Dr Evangeline Mantzioris warned that taking it incorrectly, especially before intense exercise, can cause nausea, abdominal cramping, and diarrhoea. Experts also caution that taking magnesium without a known deficiency carries risks, with very high doses potentially leading to toxicity, including low blood pressure and abnormal heart rhythms.