Vitamin D affects the absorption of folate in vitro, and perhaps of vitamin B12 (B12). However, epidemiological studies on the association of vitamin D with folate and B12 are inconclusive. We hypothesized a positive association of plasma 25-hydroxyvitamin D [25(OH)D] with folate and B12 levels in adolescents. This hypothesis was tested in a cross-sectional study of healthy adolescents (11-16 years old; n = 1416), selected from public middle schools from across Kuwait, using stratified multistage cluster random sampling. Plasma 25(OH)D was measured by LC-MS/MS. Serum B12 and total folate in hemolyzed whole blood were analyzed with commercial kits; RBC and plasma folate were calculated from total folate. Data on potential confounders were collected from the parents and adolescents. In a univariable model, 25(OH)D as a continuous variable was positively associated with each of total, RBC, and plasma folate (P < .001). After adjusting for potential confounders, this association remained significant with total folate (β = 2.0, P < .001) and red blood cell folate (β = 1.8, P < .001), but not with plasma folate (β = 0.2, P = .34). A similar pattern of association was evident when 25(OH)D was fitted as categorical variable. Correlation between B12 and 25(OH)D was weak but significant (ρ = 0.1, P < .001). 25(OH)D was positively associated with B12 in both univariable and multivariable models (P < .001) when fitted as a categorical variable only. Simultaneous quantile regression confirmed these results. We conclude that plasma 25(OH)D is positively associated with folate and B12 levels in adolescents. Properly designed large-scale randomized controlled trials are warranted to investigate the causal role of vitamin D in folate and B12 absorption.

中文翻译：

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血浆 25-羟基维生素 D 与青少年的叶酸和维生素 B12 水平呈正相关

维生素 D 影响体外叶酸的吸收，也可能影响维生素 B12 (B12) 的吸收。然而，关于维生素 D 与叶酸和 B12 关联的流行病学研究尚无定论。我们假设血浆 25-羟基维生素 D [25(OH)D] 与青少年的叶酸和 B12 水平呈正相关。这一假设在一项对健康青少年（11-16 岁；n = 1416）的横断面研究中得到检验，这些青少年选自科威特各地的公立中学，使用分层多阶段整群随机抽样。血浆 25(OH)D 通过 LC-MS/MS 测量。使用商业试剂盒分析溶血全血中的血清 B12 和总叶酸；从总叶酸计算红细胞和血浆叶酸。从父母和青少年那里收集了有关潜在混杂因素的数据。在单变量模型中，作为连续变量的 25(OH)D 与总叶酸、RBC 和血浆叶酸均呈正相关 (P < .001)。在调整潜在混杂因素后，这种关联与总叶酸 (β = 2.0, P < .001) 和红细胞叶酸 (β = 1.8, P < .001) 仍然显着，但与血浆叶酸 (β = 0.2, P = .34）。当 25(OH)D 作为分类变量拟合时，类似的关联模式很明显。B12 和 25(OH)D 之间的相关性很弱但很显着（ρ = 0.1，P < .001）。当仅作为分类变量拟合时，25(OH)D 在单变量和多变量模型中都与 B12 呈正相关 (P < .001)。同时分位数回归证实了这些结果。我们得出结论，血浆 25(OH)D 与青少年的叶酸和 B12 水平呈正相关。