Ward M, McNulty H, McPartlin J, Strain J J, Weir D G, Scott J M
Northern Ireland Centre for Diet and Health (NICHE), School of Biomedical Sciences, University of Ulster, Coleraine, BT52 1SA.
Int J Vitam Nutr Res. 2001 Jan;71(1):82-6. doi: 10.1024/0300-9831.71.1.82.
Hyperhomocysteinaemia is an established risk factor for vascular disease. The only source of homocysteine in humans is the amino acid methionine found in dietary protein. In an 8-week study, fasting plasma homocysteine concentrations were examined in a group of healthy male subjects (n = 6) under usual dietary conditions (weeks 1-4) and in response to weekly graded (25, 50 and 75 mg/kg/d) supplementary methionine (weeks 5, 6, 7). Nutrient intakes, including methionine, were calculated from 4 x 3 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 different (ANOVA) from each other ranging from 6.82 +/- 1.77 to 9.42 +/- 2.73 mumol/l. Doubling (supplementing with 25 mg/kg/d; + 2.04 g/d) or quadrupling (50 mg/kg/d; + 4.08 g/d) methionine intakes did not result in a significant increase in plasma homocysteine (8.56 +/- 3.68 mumol/l and 13.37 +/- 5.09 mumol/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 mumol/l. Mean plasma homocysteine concentration returned to baseline (8.76 +/- 3.42 mumol/l), 10 days post-supplementation. The results of this study indicate that an increased dietary methionine will only cause elevated fasting homocysteine concentrations if ingested at intakes equivalent to five times usual intake. Because it is very unlikely that such levels could be achieved through dietary means alone we conclude that plasma homocysteine is unlikely to be affected by longer-term changes in food methionine intake.
高同型半胱氨酸血症是已确定的血管疾病风险因素。人体内同型半胱氨酸的唯一来源是膳食蛋白质中的甲硫氨酸。在一项为期8周的研究中，对一组健康男性受试者（n = 6）在通常饮食条件下（第1 - 4周）以及对每周递增剂量（25、50和75 mg/kg/d）的补充甲硫氨酸（第5、6、7周）时的空腹血浆同型半胱氨酸浓度进行了检测。营养摄入量，包括甲硫氨酸，通过4次3天的食物记录进行计算。在通常饮食条件下（平均甲硫氨酸摄入量；0.95±0.51 mg/d），该组每周平均血浆同型半胱氨酸浓度彼此之间无显著差异（方差分析），范围在6.82±1.77至9.42±2.73 μmol/l之间。甲硫氨酸摄入量翻倍（补充25 mg/kg/d；增加2.04 g/d）或四倍（50 mg/kg/d；增加4.08 g/d）均未导致血浆同型半胱氨酸显著增加（分别为8.56±3.68 μmol/l和13.37±5.09 μmol/l）。然而，当以最高水平75 mg/kg/d（增加6.14 g/d）补充甲硫氨酸时，血浆同型半胱氨酸浓度显著增加，导致平均血浆同型半胱氨酸浓度为18.05±11.8 μmol/l。补充后10天，平均血浆同型半胱氨酸浓度恢复至基线水平（8.76±3.42 μmol/l）。本研究结果表明，只有当膳食甲硫氨酸摄入量达到通常摄入量的五倍时，增加的膳食甲硫氨酸才会导致空腹同型半胱氨酸浓度升高。由于仅通过饮食手段极不可能达到这样的水平，我们得出结论，血浆同型半胱氨酸不太可能受到食物中甲硫氨酸摄入量长期变化的影响。
