EFFECTIVE HOMOCYSTEINE METABOLISM MAY PROTECT SOUTH-AFRICAN BLACKS AGAINST CORONARY HEART-DISEASE

L-Methionine (0.1 g/kg body wt) was adminis tered to young white [n = 18; mean (+/- SD) age 20.0 +/- 1.0 yl and black [n = 12; mean (+/- SD) age 22.0 +/- 1.3 y] volunteers who had a similar lifestyle and who di d not differ significantly from each other with respect to plasma fola te or vitamin B-12 concentrations. Blacks, however, had significantly lower plasma pyridoxal-5'-phosphate concentrations compared with white s (P < 0.001). Fasting plasma homocysteine concentrations in blacks an d whites were not significantly different. The mean (+/- SD) maximum i ncrease in plasma homocysteine concentration measured after methionine loading was significantly lower (P < 0.01) in blacks (11.0 +/- 3.6 mu mol/L) than in whites (18.0 +/- 6.2 mu mol/L). Six weeks of vitamin s upplementation (1.0 mg folic acid, 400 mu g vitamin B-12, and 10 mg py ridoxine/d) reduced the mean (+/- SD) fasting plasma homocysteine conc entration from 9.6 +/- 3.5 to 7.2 +/- 1.6 mu mol/L in whites (P < 0.05 ) and from 8.4 +/- 2.4 to 5.6 +/- 1.4 mu mol/L in blacks (P < 0.01). T he mean (+/- SD) maximum increase in plasma homocysteine concentration after methionine loading declined from 18.0 +/- 6.2 to 11.1 +/- 2.3 m u mol/L (P < 0.01) in whites, but vitamin supplementation did not have a significant effect on the methionine-load test in black volunteers. A significant race-by-time interaction shows that blacks metabolized homocysteine more effectively than did whites, which may partly explai n their relative resistance against coronary heart disease despite a h igh prevalence of obesity, hypertension, and smoking.