Since the establishment of the 1998 folate recommended dietary allowance (RDA), the methylenetetrahydrofolate reductase (MTHFR) 677C-->T variant has emerged as a strong modifier of folate status. This controlled feeding study investigated the adequacy of the RDA, 400 microg/d as dietary folate equivalents (DFE), for Mexican American men with the MTHFR 677CC or TT genotype. Because of the interdependency between folate and choline, the influence of choline intake on folate status was also assessed. Mexican American men (n = 60; 18-55 y) with the MTHFR 677CC (n = 31) or TT (n = 29) genotype consumed 438 microg DFE/d and total choline intakes of 300, 550 (choline adequate intake), 1100, or 2200 mg/d for 12 wk. Folate status response was assessed via serum folate (SF), RBC folate, plasma total homocysteine (tHcy), and urinary folate. SF decreased (P < 0.001) 66% to 7.9 +/- 0.7 nmol/L (means +/- SEM) in men with the 677TT genotype and 62% to 11.3 +/- 0.9 nmol/L in the 677CC genotype. Plasma tHcy increased (P < 0.0001) 170% to 31 +/- 3 micromol/L in men with the 677TT genotype and 18% to 11.6 +/- 0.3 micromol/L in the 677CC genotype. At the end of the study, 34% (677TT) and 16% (677CC) had SF concentrations <6.8 nmol/L and 79% (677TT) and 7% (677CC) had tHcy concentrations >14 micromol/L. Choline intake did not influence the response of the measured variables. These data showed that the folate RDA is not adequate for men of Mexican descent, particularly for those with the MTHFR 677TT genotype, and demonstrated a lack of influence of choline intake on the folate status variables measured in this study.
These data suggest that 550 mg choline/d is sufficient for preventing elevations in serum markers of liver dysfunction in this population under the conditions of this study; higher intakes may be needed to optimize other endpoints.
This controlled feeding study investigated the influence of choline intake ranging from 300 to 2200mg/d on biomarkers of choline status. Mexican American men (n=60) differing in methylenetetrahydrofolate reductase (MTHFR) C677T genotype (29 677TT, 31 677CC) consumed a diet providing 300mg/d choline plus supplemental choline intakes of 0, 250, 800 or 1900 mg/d for total choline intakes of 300, 550 (choline AI), 1100 or 2200mg/d, respectively for 12‐wk; 400mcg/d as dietary folate equivalents and 173mg/d betaine were consumed throughout the study. Plasma choline and betaine increased (P<0.05) in response to 550, 1100 and 2200mg/d choline (2200>1100=550) whereas no change was observed on the 300mg/d group. Plasma phosphatidylcholine declined (P<0.05) in response to 300mg/d possibly due to declining folate status; no changes were observed in the other choline intake groups. After a methionine load, choline intakes of 1100 and 2200 mg/d groups attenuated (P<0.006) the rise in plasma tHcy relative to the 300 and 550 mg/d groups. No changes in plasma ALT or AST concentrations were detected regardless of choline intake. These data suggest that 550 mg/d choline is sufficient to prevent liver dysfunction in this population; higher intakes are needed to optimize other measured end‐points. Supported by NIH Grant #S06GM053933.
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