|Nielsen, Forrest - Frosty|
Submitted to: Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/15/2002
Publication Date: 5/1/2002
Citation: Lukaski, H.C., Nielsen, F.H. 2002. Dietary magnesium depletion affects metabolic responses during submaximal exercise in postmenopausal women. Journal of Nutrition. 132:930-935. Interpretive Summary: Knowledge of the amount of magnesium needed for health and optimal function is lacking, particularly among older women. The current recommendation for daily dietary intake of magnesium for women is inferred from very limited data. We undertook this study to determine the amount of dietary magnesium that is needed to ensure that intake equals losses in the urine and feces. We also sought to compliment this approach with measurements of magnesium in the blood and muscle as well as determinations of energy use during low level work in 10 postmenopausal women. When dietary magnesium was low (about 200 mg per day) compared to adequate (320 and 380 mg/d), body losses exceeded dietary intake, magnesium was lost from body stores, muscle magnesium concentration decreased, and oxygen use during low intensity exercise was increased. These findings indicate that a daily intake of magnesium of 320 mg/d is needed to support life sustaining functions. This value is similar to the recent recommendation by the National Academy of Sciences for women aged 51 through 70 years of age. Therefore, this study provides the first confirmation of the current recommended dietary allowance (RDA) for magnesium based on different criteria than were used to develop the RDA. This information will be useful to dietitians, nutritionists and public health specialists who seek to promote health and optimal function and performance of the US population.
Technical Abstract: Although magnesium is recognized as an essential mineral for humans, national nutritional surveys report that dietary magnesium does not meet recommendations for intake. This study examined the effects of dietary magnesium restriction on biochemical measures of magnesium nutritional status and physiological responses during submaximal exercise. Ten postmenopausal women consumed diets containing conventional foods with varying magnesium content including control (100 mg/2000 kcal supplemented with 200 mg/d for 35 d), depletion (100 mg/d for 93 d) and repletion (100 mg/2000 kcal supplemented with 200 mg/d for 49 d). The ratio of ultra filterable to serum magnesium increased (p<0.05), magnesium retention and skeletal muscle magnesium concentration decreased (p<0.05) when dietary magnesium was low. Peak oxygen uptake, total and cumulative oxygen uptake and peak heart rate increases (p<0.05) during submaximal work with restricted compared to increased dietary magnesium. These findings indicate that dietary magnesium deficiency can be induced in otherwise healthy women and that impaired magnesium nutriture increases energy needs and adversely affects cardiovascular function during submaximal work.