Extra dietary copper inhibits LDL oxidation

US Department of Agriculture, Agricultural Research Service Grand Forks Human Nutrition Research Center PO Box 9034 Grand Forks, ND 58202-9034 E-mail: lklevay{at}gfhnrc.ars.usda.gov

Wan et al (1) fed cocoa powder and dark chocolate to subjects for 4 wk and found that LDL oxidation was inhibited in vitro. This favorable effect on cardiovascular risk status was attributed to flavonoids, a group of polyphenolic compounds with antioxidant characteristics. An increase in dietary copper during this experiment may have contributed to their results.

The Western diet often is low in copper: approximately one-third of 849 diets that were analyzed provided 1 mg/d (2). The interquartile range was 0.91–1.86 mg/d. Milk chocolate and cocoa powder are in the upper quartile of 235 foods evaluated by Lurie et al (3), ranking 186 and 232, respectively, in copper concentration. Calculations using Lurie et al’s values for chocolate and cocoa powder of 2.86 and 50.0 µg/g, respectively, show that these supplements would have added nearly 1.15 mg Cu to the basal diet each day. Dark chocolate contains more copper than does light chocolate and would have increased this estimated amount even more. It seems likely that the total daily intake of copper might have been 3 times the daily estimated average requirement (0.7 mg) or twice the recommended dietary allowance (0.9 mg) for adults (4).

Although copper salts (at 10 µmol/L) and LDL are highly reactive in vitro, this phenomenon is probably irrelevant to human physiology because copper ions are virtually nonexistent (1 amol/L) in vivo (5–7). Indeed, after providing copper supplementation to middle-aged subjects, Rock et al (8) found that the subjects’ erythrocytes were more resistant to oxidation in vitro. Although this improvement occurred without an increase in the activity of superoxide dismutase (EC 1.15.1.1), an enzyme that provides defense against oxidative damage, the results may indicate that the subjects ordinarily ate too little copper and had other means of defense.

Perhaps the usual copper intakes of the subjects studied by Wan et al were too low also. Their basal diet probably was low in copper because it excluded beans and soybeans, 2 foods in the top quartile (see above). Control of the diets for copper intake as well as for intakes of caffeine, cholesterol, fat, and fiber would have been informative because the increased copper intake from chocolate seems smaller than some beneficial amounts given by Rock et al (8). Perhaps chocolate enhances the absorbability of copper.

Copper is an antioxidant nutrient for cardiovascular health (7) and has no prooxidant activity at a considerably higher intake (8) than that given by Wan et al. Diets low in copper are suggested as an explanation for much of the epidemiology and pathophysiology of ischemic heart disease (9). Chocolate is a pleasant dietary supplement.

REFERENCES

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9. Klevay LM. Trace element and mineral nutrition in disease: ischemic heart disease. In: Bogden JD, Klevay LM, eds. Clinical nutrition of the essential trace elements and minerals: the guide for health professionals. Totowa, NJ: Humana Press Inc, 2000:251–71.