Effect of orange juice, folic acid, and oral contraceptives on serum folate in women taking a folate-restricted diet

Plasma concentration of folate as a biomarker for the intake of fruit and vegetables: the Hordaland Homocysteine Study

BACKGROUND

Nutritional biomarkers may be used to assess dietary exposure without the errors commonly associated with self-reported dietary data.

OBJECTIVE

The objective was to examine the association between plasma folate and intake of folate, fruit, and vegetables in a large cohort of healthy adults consuming foods that had not been fortified with folic acid.

DESIGN

The present study population included 5533 middle-aged (47-49 y) and old (71-74 y) subjects from the Hordaland Homocysteine Study. The participants completed a food-frequency questionnaire and provided blood samples for chemical analyses.

RESULTS

We observed a significant difference in plasma concentrations of folate across increasing quartiles of fruit, vegetable, and orange juice consumption. The difference in plasma folate between the highest and lowest quartiles was 1.97 (95% CI: 1.86, 2.07) nmol/L for fruit intake, 1.79 (95% CI: 1.69, 1.89) nmol/L for vegetable intake, and 2.69 (95% CI: 2.51, 2.87) nmol/L for orange juice intake. A significant inverse relation was observed across increasing quartiles of milk and bread intakes. The difference between the highest and lowest quartiles was -1.03 (95% CI: -1.13, -0.92) nmol/L for milk and -1.60 (95% CI: -1.69, -1.50) nmol/L for bread.

CONCLUSION

Plasma folate concentration may be a useful biomarker for the intake of fruit and vegetables in populations consuming unfortified food products. The association can be attenuated by and should be corrected for individual intake of folic acid supplements.

Case study: folate bioavailability

Folate nutritional status depends on intake from food and supplements as well as on the bioavailability of the various ingested forms of this vitamin. Although many advances in the understanding of folate bioavailability have occurred in recent years, many areas of uncertainty remain, especially with respect to naturally occurring dietary folate. This review includes a summary of factors that affect folate absorption and utilization, currently used and promising methods suitable for the assessment of bioavailability, significant findings on which current understanding is based and research needs.

Organic Acids in Selected Foods Inhibit Intestinal Brush Border Pteroylpolyglutamate Hydrolase in Vitro: Potential Mechanism Affecting the Bioavailability of Dietary Polyglutamyl Folate

Dietary folates exist largely as polyglutamates that require deconjugation prior to absorption. This process is catalyzed by intestinal pteroylpolyglutamate hydrolase (PPH) mainly associated with the jejunal brush border membrane. Previous studies have shown that citrate ion as well as the soluble fraction of many foods can inhibit PPH in vitro. This study was conducted to characterize further the in vitro inhibition of porcine PPH by fractions of selected foods (orange juice, tomatoes, and lima beans) and by organic anions to evaluate potential effects on bioavailability. Organic anions tested were competitive inhibitors with respect to the polyglutamyl folate substrate, with the following K(i) values: citrate, 6.42 mmol/L; malate, 10.1 mmol/L; phytate, 6.48 mmol/L; ascorbate, 19.6 mmol/L. Neutralized orange juice in the reaction mixture strongly inhibited PPH activity, while neutralized tomato homogenate caused weaker inhibition and lima bean homogenate inhibited much more weakly, all with kinetics indicating competitive inhibition. Fractionation of food extracts indicated that the inhibitors were anions of low molecular mass (<6-8 kDa). Chromatographic separation followed by in vitro assay indicated that citrate was the major inhibitor, with lesser inhibition by malate and phytate. These results indicate the potential for dietary constituents to retard the action of intestinal brush border PPH, with possible inhibitory effects on the bioavailability of polyglutamyl folates. The in vivo significance of this effect would depend on the extent of inhibition relative to the total intestinal PPH activity.

[Dietary folates--a timely review. Stability, physiological significance, bioavailability, analytical determination methods, effect of food handling]

Because of the unequal and, in some instances, low stability of different folate vitamers against extreme conditions the analytical determination of folate and the estimation of folate losses in food processing and preparation cause considerable difficulties. HPLC allows determination of the native folate derivative patterns. As the bioavailability of folates is influenced by a variety of factors and different methods were employed for assessing bioavailability there is a considerable inconsistency in the results of these studies. Folates labeled with radioactive or stable isotopes provide new approaches to metabolic and bioavailability studies.

Investigation of folate intake and metabolism in women who have had two pregnancies complicated by neural tube defects

OBJECT

To investigate folate intake and blood levels of folic acid and vitamin C in women with and without a history of two NTD-affected pregnancies and to measure the increase in serum folate following ingestion of orange juice.

SUBJECTS

Sixteen women with a history of two NTD-affected infants and 16 controls with no such history, none of whom were either pregnant or taking vitamin supplements. The orange juice loading test was carried out on eight matched pairs.

MAIN OUTCOME MEASURES

Dietary intake of folate was assessed by questionnaire and blood levels of folate and vitamin C were measured.

RESULTS

There was no evidence of decreased intake of folate in subjects who had had two NTD-affected pregnancies. In controls, both serum and red cell folate showed significant correlation with dietary folate, while in subjects there was no such correlation. Subjects also had smaller increases in serum folate following an oral load than controls, although the differences were not significant.

CONCLUSION

Women who have had two NTD-affected pregnancies may have defective folate metabolism. Further investigations on short term utilisation of ingested food folates in these women are required.

Influence of oral contraceptives on drug therapy

Interferences between drugs and oral contraceptives are considered to alter pharmacokinetics and thus the efficacy of steroidal hormones. It should be noted, however, that steroids can also modify the metabolism and pharmacodynamic effects of various substances. To the present knowledge, phase I (i.e., oxidation, demethylation) and phase II reactions (conjugation) are concerned. Drugs sharing those enzymatic systems with oral contraceptives experience either an increase in bioavailability by inhibition of oxidative metabolism or undergo accelerated elimination by induced conjugation. Such interaction may be of practical interest in subjects who take oral contraceptives and are simultaneously treated with antidepressants, antihypertensives, insulin, synthetic glucocorticoids, theophylline, and caffeine.

Acute folic acid deficiency after bone marrow transplantation

After bone marrow transplantation (BMT), megaloblastic bone marrow changes are often observed that can only be partially explained by drug effects. Our goal was to find out whether folic acid deficiency represented an additional factor. The serum folic acid concentrations of 41 patients were determined regularly before and after BMT. A 2nd degree polynomial regression analysis revealed a clear and acute drop in folic acid concentrations within 7-9 days after BMT. In 19 patients the level fell below 3.0 ng/ml, the range of folic acid deficiency. The mean folic acid values without oral administration of folic acid after BMT lay significantly below the mean values with substitution (P less than 0.001). If a case of acute graft versus host disease (GvHD) was more severe than grade I, the mean folic acid levels were significantly lower (P less than 0.01). Patients with megaloblastic bone marrow changes after BMT had significantly lower folic acid values than those without such changes (P less than 0.01). The 18 patients with folic acid deficiency had a significantly higher rate of megaloblasts, binucleate erythropoietic precursors, Howell-Jolly bodies, giant myelocytes, and giant metamyelocytes in bone marrow smears than the remaining 23 patients (P less than 0.05). Folic acid deficiency did not slow down the increase in leukocytes, granulocytes, thrombocytes, or reticulocytes after BMT. There were 8.2%-9.7% hypersegmented neutrophils in the blood (normal 5%) after BMT both with and without folic acid deficiency. Folic acid deficiency after BMT was caused by insufficient intake combined with simultaneous decreased intestinal resorption and increased requirements for the regeneration of bone marrow and intestinal mucosa.