Submitted to: Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2003
Publication Date: July 1, 2003
Citation: Nielsen, F.H., Milne, D,B. 2003. Some magnesium status indicators and oxidative metabolism responses to low-dietary magnesium are affected by dietary copper in postmenopausal women. Nutrition. 19:617-626. Interpretive Summary: In both animals and humans, dietary deficiencies of magnesium and copper can adversely affect cardiovascular (heart) and bone health. Thus, a study with human volunteers was conducted with the objective of ascertaining whether a low intake of copper would worsen the response to a deficient intake of magnesium. Nineteen postmenopausal women aged 47 to 78 years completed a metabolic unit study as designed. For 162 days, 9 women were fed a diet supplying copper in an amount (1.0 mg per 2000 calories) close to the recommended dietary allowance (RDA) of 0.7 mg per day; this was designated as a low dietary copper intake. During the same time, 10 women were fed a diet that contained 3.0 mg of copper per 2000 calories; this amount is a high, but achievable dietary intake, and was designated as a luxuriant copper intake. The diets supplied either 99 (deficient) or 399 (adequate) mg of magnesium per 2000 calories for 81 days in a crossover design. In this design, half of the women fed low and luxuriant copper consumed the deficient magnesium diet for the first 81 days, then switched to the adequate magnesium diet for the final 81 days. The other half of the women consumed the two magnesium intakes in the opposite order. Magnesium balance (intake minus that loss in feces and urine) was highly positive when magnesium was adequate, but was not positive when magnesium was deficient. Copper intake did not affect this response but did affect other responses including some that could affect heart health. The order in which magnesium restriction occurred also affected the response to this treatment. When the magnesium adequate diet was fed first many of the responses to magnesium deficiency were muted, most likely because magnesium was stored and used to prevent changes induced by its deficiency. A longer low dietary magnesium period apparently was needed to deplete the stores. The findings indicate that the effects of consuming a magnesium deficient diet can by influenced by the length of time on the diet, prior magnesium status, and dietary copper intake, and that 100 mg of magnesium per day is inadequate to prevent changes that could be detrimental to heart and bone health.
Technical Abstract: In both animals and humans, deficiencies of both magnesium and copper result in undesirable changes in lipid and reactive oxygen metabolism that can adversely affect cardiovascular and bone health. Thus, a study with human volunteers was conducted with the objective of ascertaining whether a low intake of copper would exacerbate the response to a deficient intake of magnesium. Nineteen postmenopausal women aged 47 to 78 years completed a metabolic unit study as designed. For 162 d, 9 women were fed a diet containing 1.0 mg Cu/2000 kcal and 10 women were fed 3.0 mg Cu/2000 kcal. Diets contained either 99 or 399 mg Mg/2000 kcal for 81 d in a randomized, double-blind, crossover design. Magnesium balance was highly positive when the dietary magnesium was high, but was non-positive when dietary magnesium was low. Copper balance was more positive when dietary copper was high than when it was low. Plasma ionized magnesium was decreased by magnesium deprivation. Several variables measured indicated that low dietary copper affected the response to magnesium deprivation or vice versa. Red blood cell magnesium was lower when dietary copper was low than when it was high. When dietary magnesium was low, serum copper was lower in the women fed marginal copper than in those fed luxuriant copper. When dietary magnesium was high, low dietary copper did not affect serum copper. Magnesium deprivation decreased red blood cell superoxide dismutase when dietary copper was luxuriant; when dietary copper was low, magnesium deprivation did not have much of an effect. Apolipoprotein A-1was the lowest when both dietary magnesium and copper were low. The order in which the magnesium restriction occurred affected the response of a number of variables to this treatment including concentrations of serum magnesium, total and LDL-cholesterol, triglycerides and apolipoprotein B; and red blood cell glutathione peroxidase activity and copper and magnesium concentrations. The findings indicate that in short term magnesium depletion experiments the response to depletion can be influenced by other dietary factors including prior magnesium status and copper intake, and that 100 mg Mg/d is inadequate for postmenopausal women.