Effect of supplemental methionine on plasma homocysteine concentrations inhealthy men: A preliminary study

Hyperhomocysteinaemia is an established risk factor for vascular disease. T he only source of homocysteine in humans is the amino acid methionine found in dietary protein. In an 8-week study fasting plasma homocysteine concent rations were examined in a group of healthy male subjects (n = 6) under usu al dietary conditions (weeks 1-4) and in response to weekly graded (25, 50a nd75mg/kg/d) supplementary methionine (weeks 5, 6, 7). Nutrient intakes, in cluding methionine, were calculated from 4x3 day food records, Under usual dietary conditions (mean methionine intake; 0.95 +/- 0.51 mg/d) weekly mean plasma homocysteine concentrations for the group were not significantly di fferent (ANOVA) from each other ranging from 6.82 +/- 1.77 to 9.32 +/- 2.73 mu mol/l. Doubling (supplementing with 25 mg/kg/d; + 2.04 g/d) or quadrupl ing (50 mg/kg/d; + 4.05 g/d) methionine intakes did not result in a signifi cant increase in plasma homocysteine (8.56 +/- 3.65 mu mol/l and 13.37 +/- 5.09 mu mol/l respectively). A significant increase, however, was achieved when diets were supplemented with methionine at the highest level of 75 mg/ kg/d (+ 6.14 g/d) resulting in a mean plasma. homocysteine concentration of 18.05 +/- 11.8 mu mol/l. Mean plasma homocysteine concentration returned t o baseline (8.76 +/- 3.42 mu mol/l), 10 days post-supplementation. The resu lts of this study indicate that an increased dietary methionine will only c ause elevated fasting homocysteine concentrations if ingested at intakes eq uivalent to five times usual intake. Because it is very unlikely that such levels could be achieved through dietary means alone we conclude that plasm a homocysteine is unlikely to be affected by longer-term changes in food me thionine intake.