Dietary copper, simple sugars, and metabolic changes in pigs

Some magnesium status indicators and oxidative metabolism responses to low-dietary magnesium are affected by dietary copper in postmenopausal women

OBJECTIVE

A study with human volunteers was conducted to ascertain whether a low intake of copper (Cu) would exacerbate the response to a deficient intake of magnesium (Mg).

METHODS

Nineteen postmenopausal women, age 47 to 78 y, completed a metabolic unit study as designed. For 162 d, nine women were fed a diet containing 1.0 mg of Cu/2000 kcal and 10 women were fed 3.0 mg of Cu/2000 kcal. Diets contained 99 or 399 mg of Mg/2000 kcal for 81 d in a randomized, double-blind, crossover design. Differences were considered significant when statistical analysis yielded P </= 0.05.

RESULTS

Magnesium balance was highly positive when the dietary magnesium was high but 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 A1 was lowest when 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 and total and low-density lipoprotein cholesterol.

CONCLUSIONS

The findings indicated that, in short-term magnesium depletion experiments, the response to depletion can be influenced by other dietary factors including copper intake and a high magnesium intake before depletion, and that 100 mg of Mg/d is inadequate for postmenopausal women.

Newer aspects of micronutrients in chronic disease: copper

Cu ions are pro-oxidants when added to biological material in vitro and excessive levels of Cu in the body, such as in Wilson's Disease (Yarze et al. 1992) promote oxidant-related pathologies. In contrast there is now substantial evidence that an optimum level of Cu is required to maintain antioxidant defence and that Cu deficiency in animals increases oxidant stress. There are abundant mechanistic relationships linking Cu deficiency and processes associated with IHD, some of which do not directly involve oxidant damage. These mechanistic relationships, however, have mostly been demonstrated in animal models and more information is urgently required concerning possible chronic mild Cu deficiencies in human populations. A major hurdle to advances in this area is the lack of indices of Cu status which are sensitive enough to detect marginal Cu deficiency in humans. The question, therefore, of whether or not there is a role for mild Cu deficiency in the onset of chronic disease processes, including IHD, remains unanswered.

Copper deficiency in rats: the effect of clofibrate

This study was undertaken to determine whether hepatic lipogenesis plays a role in the exacerbation of copper (Cu) deficiency. Forty-eight male rats were fed from weaning a Cu-deficient or adequate diet containing 62% carbohydrate as either starch or fructose with or without clofibrate for 5 weeks. Clofibrate was fed since it had been shown to possess hypolipidemic properties. Administration of clofibrate reduced the activity of the lipogenic enzyme glucose-6-phosphate dehydrogenase. Total hepatic lipid, however, was not reduced. Clofibrate did not affect hepatic lipid concentration and the pathology associated with Cu deficiency when fructose was fed was not prevented by the consumption of clofibrate.