• Alida Melse-Boonstra, Pål I Holm, Per M Ueland, Margreet Olthof, Robert Clarke, and Petra Verhoef.
• Wageningen Centre for Food Sciences and the Division of Human Nutrition, Wageningen University, Wageningen, Netherlands.
• Am. J. Clin. Nutr. 2005 Jun 1;81(6):1378-82.

BackgroundRemethylation of homocysteine to methionine can occur through either the folate-dependent methionine synthase pathway or the betaine-dependent betaine-homocysteine methyltransferase pathway. The relevance of betaine as a determinant of fasting total homocysteine (tHcy) is not known, nor is it known how the 2 remethylation pathways are interrelated.ObjectiveThe objectives of the study were to examine the relation between plasma betaine concentration and fasting plasma tHcy concentrations and to assess the effect of folic acid supplementation on betaine concentrations in healthy subjects.DesignA double-blind randomized trial of 6 incremental daily doses of folic acid (50-800 microg/d) or placebo was carried out in 308 Dutch men and postmenopausal women (aged 50-75 y). Fasted blood concentrations of tHcy, betaine, choline, dimethylglycine, and folate were measured at baseline and after 12 wk of vitamin supplementation.ResultsConcentrations of tHcy were inversely related to the betaine concentration (r = -0.17, P < 0.01), and the association was independent of age, sex, and serum concentrations of folate, creatinine, and cobalamin. Folic acid supplementation increased betaine concentration in a dose-dependent manner (P for trend = 0.018); the maximum increase (15%) was obtained at daily doses of 400-800 microg/d.ConclusionsThe plasma betaine concentration is a significant determinant of fasting tHcy concentrations in healthy humans. Folic acid supplementation increases the betaine concentration, which indicates that the 2 remethylation pathways are interrelated.

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