A female over age 31 should get at least 310 mg of magnesium a day according to the Recommended Daily Allowance (RDA).* *National Institute of Health, "Magnesium: What Is It?" Office of Dietary Supplements, NIH website: http://ods.od.nih.gov/factsheets/Magnesium-QuickFacts/
Intense physical activity can cause sweating that can lead to magnesium loss from your body.* *Lukaski HC. Magnesium, zinc, and chromium nutriture and physical activity. Am J Clin Nutr.2000;72(2 Suppl):585S-593S.