Relation of body mass index to blood folate and total homocysteine concentrations in Japanese adults.

PURPOSE Plasma folate concentrations are suggested to be negatively associated with body mass index (BMI, kg/m(2)), although these findings are controversial. Our objective was to evaluate the association of BMI with blood folate and total homocysteine (tHcy) concentrations. METHODS We measured plasma and erythrocyte folate and plasma tHcy concentrations in 434 healthy adults (343 women and 91 men; mean age of 63.8 ± 10.7 [SD, range 23-88] years), who participated in a 2007 population-based survey in western Japan. RESULTS The overall mean plasma and erythrocyte folate and tHcy were 21.6 (±11.0, SD) nmol/L, 844 (±291) nmol/L and 11.6 (±3.9) μmol/L, respectively. The mean BMI was 22.8 (±3.0; 15.6-33.3) kg/m(2), and only 72 subjects (17%) had BMI > 26.0 kg/m(2). Mean plasma folate decreased as BMI increased (p-trend < 0.01), whereas mean erythrocyte folate and plasma tHcy were similar regardless of BMI (p-trends = 0.49 and 0.28, respectively). CONCLUSION Our data indicate that the interpretation of plasma folate concentrations to assess folate nutritional status is complicated by BMI, although the impact of BMI on plasma folate was relatively small. It is important to take this association into account for the selection of subjects for future large-scale studies. The mechanism of this inverse association between BMI and plasma folate concentrations should be investigated.