Hibler EA, et al. - In this investigation involving 20,295 National Health and Nutrition Examination Survey participants (1999–2006) aged > 20 years with complete dietary, physical activity, and mortality data (2,663 deaths), researchers ascertained if levels of magnesium and calcium and the ratio of dietary calcium to magnesium (Ca:Mg) intake modify the connection between physical activity and mortality. Higher physical activity was found to be associated significantly with reduced risk of total mortality and cause-specific mortality, irrespective of Ca:Mg ratio, magnesium or calcium intake. In contrast, when magnesium intake was above the RDA level, both moderate and high physical activity were significantly linked to significantly reduced mortality risks due to cancer. Higher physical activity was also found to be significantly linked to a reduced risk of cancer mortality only when Ca:Mg ratios were between 1.7–2.6, although the interaction was not significant. Overall, dietary magnesium and the Ca:Mg ratio potentially change the link between physical activity and cause-specific mortality. Further study is important for understanding the modifying effects on chronic disease prevention of the balance between calcium and magnesium intake on physical activity.