Prevention of Neural-Tube Defects with Periconceptional Folic Acid, Methylfolate, or Multivitamins?

Background/Aims: To review the main results of intervention trials which showed the efficacy of periconceptional folic acid-containing multivitamin and folic acid supplementation in the prevention of neural-tube defects (NTD). Methods and Results: The main findings of 5 intervention trials are known: (i) the efficacy of a multivitamin containing 0.36 mg folic acid in a UK nonrandomized controlled trial resulted in an 83–91% reduction in NTD recurrence, while the results of the Hungarian (ii) randomized controlled trial and (iii) cohort-controlled trial using a multivitamin containing 0.8 mg folic acid showed 93 and 89% reductions in the first occurrence of NTD, respectively. On the other hand, (iv) another multicenter randomized controlled trial proved a 71% efficacy of 4 mg folic acid in the reduction of recurrent NTD, while (v) a public healthoriented Chinese-US trial showed a 41–79% reduction in the first occurrence of NTD depending on the incidence of NTD. Conclusions: Translational application of these findings could result in a breakthrough in the primary prevention of NTD, but so far this is not widely applied in practice. The benefits and drawbacks of 4 main possible uses of periconceptional folic acid/multivitamin supplementation, i.e. (i) dietary Received: May 30, 2011 Accepted after revision: July 8, 2011 Published online: August 25, 2011 Andrew E. Czeizel Foundation for the Community Control of Hereditary Diseases Törökvész lejtõ 32 HU–1026 Budapest (Hungary) Tel. +36 1394 4712, E-Mail czeizel @ interware.hu © 2011 S. Karger AG, Basel 0250–6807/11/0584–0263$38.00/0 Accessible online at: www.karger.com/anm D ow nl oa de d by : 54 .1 91 .4 0. 80 9 /1 6/ 20 17 9 :2 3: 37 P M Czeizel /Dudás /Paput /Bánhidy Ann Nutr Metab 2011;58:263–271 264 undernutrition could be the common factor in the origin of NTD. His group tested the effect of diet supplemented with a multivitamin containing 0.36 mg folic acid in the first intervention trial. Women who had had one or more previous infants with NTD were supplemented by this multivitamin during the periconceptional period while controls were recruited among similar women who were already pregnant without vitamin supplementation. The results of this intervention study were published separately for the Yorkshire region of the UK [1] and Northern Ireland [2] , and they found 91 and 83% reductions in NTD recurrence, respectively. However, their results were not accepted by some experts because of possible selection bias in their non-randomized controlled trial (RCT). Thus the Medical Research Council (MRC) in the UK organized a multicenter RCT (43% of the participants came from Hungary). There were 4 supplementation groups: folic acid (4 mg), other vitamins, folic acid + other vitamins, and minerals as the control. The MRC Vitamin Study found that a pharmacological dose (4 mg) of folic acid alone can reduce NTD recurrence by 71% (0.8 vs. 4.3%; RR 0.29; 95% CI 0.12– 0.71) [3] . Periconceptional multivitamin supplementation was incorporated into the Hungarian Periconception Service (HPS) launched in 1984 [4] as an RCT. Half of the participants were supplied a micronutrient combination (the so-called ‘multivitamin’ contained 12 vitamins, among them folic acid 0.8 mg, B 12 4.0 g, B 6 2.6 mg, and B 2 1.8 mg, 4 minerals, and 3 trace elements), while the other half of the participants were supplied a placebolike trace element combination, i.e. ‘no multivitamin’, randomly. These women used the supplements at least for 1 month before conception and at least for 2 months after conception because the critical period of anencephaly is between the 35th and 40th gestational days, while spina bifida had this period between the 37th and 42nd gestational days. There were 2 major questions regarding the Hungarian RCT following the publications of the above two ‘recurrence’ studies: (i) Do folic acid-containing multivitamins reduce the risk of the first occurrence of NTD? About 95% of women who have a fetus or infant with NTD had no previous NTD pregnancies; thus the prevention of their first occurrence would be a real public health success. (ii) The pharmacological dose (4 mg) of folic acid used in the MRC Vitamin Study might have some adverse effects; thus an objective was to evaluate the physiological dose (1 mg or less) of folic acid. The trial tested the efficacy of a multivitamin containing 0.8 mg folic acid. NTD did not occur in 2,391 offspring of the multivitamin group, while 6 NTD were found in 2,471 offspring of the no-multivitamin group (p = 0.01; RR 0.07; 95% CI 0.01–0.13). Thus, the Hungarian RCT demonstrated first that a multivitamin containing 0.8 mg folic acid prevented at least 90% of the first occurrences of NTD [5] . For ethical reasons, the Hungarian RCT could not be continued; thus a cohort-controlled trial (CCT) was designed to collect more data regarding the preventive effect of this multivitamin for NTD and other CAs. All participants in the HPS were supplied the multivitamin used in RCT, while women for the unsupplemented cohort were recruited in the 14th week of pregnancy without vitamin use from the regional prenatal care clinics and they were matched to each pregnant woman of the supplemented cohort. The protective effect of this multivitamin for the reduction of NTD was confirmed in these 3,056 ‘pairs’ (1 vs. 9; OR 0.11; 95% CI 0.01–0.91) [6] . These Hungarian intervention trials showed the efficacy of this multivitamin in the reduction of some other CAs, and mainly cardiovascular CAs, but these data are not discussed here. Later, the efficacy of 0.4 mg folic acid for the prevention of the first occurrence of NTD was shown in a Chinese-US study [7] . There was a 79% reduction in the risk of NTD in areas with high rates of NTD (6.5 per 1,000), while this reduction was 41% in areas with low rates of NTD (0.8 per 1,000). Many observational studies of folic acid-containing multivitamins or folic acid alone were also published, which confirmed the prevention of NTD, but only the data of intervention trials were summarized above. Hyperhomocysteinemia-Related NTD The origin of NTD can be explained by the interaction of genes and environmental factors (such as dietary deficiency). Several genetic and environmental factors contribute to the origin of NTD; here only the most established one, i.e. hyperhomocysteinemia, is discussed. The natural polyglutamate folate was discovered by Lucy Wills [8] 80 years ago and she recommended using the term vitamin 11 as a ‘twin’ of vitamin B 12 . Later the monoglutamate form of this vitamin was synthesized [9] . Humans cannot produce folate. The major dietary sources of folates are fresh and frozen green leafy vegetables, citrus fruits and juices, liver, wheat bread, and legumes such as beans. Thus the requirement of this water-soluble vitamin is supplied partly by dietary intakes of folates D ow nl oa de d by : 54 .1 91 .4 0. 80 9 /1 6/ 20 17 9 :2 3: 37 P M Prevention of NTD with Folic Acid, Methylfolate, or Multivitamis? Ann Nutr Metab 2011;58:263–271 265 and partly by the use of synthetic folic acid, and to estimate doses we have to add these two forms of this vitamin. After dietary intake of polyglutamate folates and the intended supply of synthetic monoglutamate folic acid, these undergo absorption in the cells of the upper small intestine ( fig. 1 ). Folic acid can absorb directly, while folate is changed into the monoglutamate form by conjugase enzymes. In the next step these monoglutamates are converted to dihydrofolate and then to tetrahydrofolate (THF) by reductase enzymes. THF is the parent compound of all biologically active forms of this vitamin. THF is converted to 5,10-methylene-THF and 5-methylene-THF (5-MTHF) before transfer into the hepatic portal vein which then leads to the liver and onwards to the systemic blood circulation and all body tissues. When meat, fish, or plant proteins are digested, amino acids, e.g. methionine, are released, and methionine is converted to homocysteine. Homocysteine is a toxic metabolite; therefore, humans neutralize it normally as soon as possible. On the one hand, homocysteine is metabolized via the transsulfuration pathway to form cystathionine catalyzed by cystathionine  -synthase and serine hydroxymethyltransferase. Cystathionine -synthase requires pyridoxal 5 -phosphate, i.e. vitamin B 6 , as a cofactor. On the other hand, remethylation of homocysteine to methionine is catalyzed by methionine synthase. This enzyme requires vitamin B 12 as a cofactor and 5-MTHF as the methyl donor. The latter explains the importance of folate-folic acid deficiency in the origin of NTD. The most important cause of hyperhomocysteinemia and/or a lack of methionine is the polymorphism of the MTHF-reductase (MTHFR) gene. The MTHFR:c.677C 1 T mutation has been identified and it results in a thermolabile variant (Ala225Val) of the MTHFR enzyme with a 40% reduction in its activity of CT (heterozygote) and with very low (about 70% reduction) activity of the TT (homozygote) forms. Vitamin B 2 is a cofactor of the MTHRF enzyme. The enzyme variants due to its mutant gene pairs cannot effectively catalyze the pathway of Vitamin B11