Abstract
The vitamin folate is recognized as beneficial health-wise in the prevention of neural tube defects, anemia, cardiovascular diseases, poor cognitive performance, and some forms of cancer. However, suboptimal dietary folate intake has been reported in a number of countries. Several national health authorities have therefore introduced mandatory food fortification with synthetic folic acid, which is considered a convenient fortificant, being cost-efficient in production, more stable than natural food folate, and superior in terms of bioavailability and bioefficacy. Other countries have decided against fortification due to the ambiguous role of synthetic folic acid regarding promotion of subclinical cancers and other adverse health effects. This paper reviews recent studies on folate bioavailability after intervention with folate from food. Our conclusions were that limited folate bioavailability data are available for vegetables, fruits, cereal products, and fortified foods, and that it is difficult to evaluate the bioavailability of food folate or whether intervention with food folate improves folate status. We recommend revising the classical approach of using folic acid as a reference dose for estimating the plasma kinetics and relative bioavailability of food folate.
Highlights
The preventive effect of high folic acid intake against neural tube defects (NTD) is considered one of the most important nutritional discoveries in the period 1976–2006 [1]
It is commonly assumed that food folates, which mainly exist in their polyglutamyl form, are absorbed in the jejunum as monoglutamyl folates after removal of the polyglutamyl chain by intestinal γ-glutamyl hydrolase [27], and thereafter reduced and methylated in the enterocyte
Current short-term folate bioavailability data are limited to a few vegetables, fruits, cereal products, and fortified foods (Table 3) [18,40,45,65,70,78] and have to be interpreted with caution. This summary of existing information shows that only limited folate bioavailability data are available for vegetables, fruits, cereal products and fortified foods
Summary
The preventive effect of high folic acid intake against neural tube defects (NTD) is considered one of the most important nutritional discoveries in the period 1976–2006 [1]. Recent publications question the validity of the conventional approach used in bioavailability studies comparing folic acid with natural food folate [19], and demand approaches using whole diets rather than single foods [11] or data from meta-analyses of controlled feeding trials [23] in order to closer elucidate post-absorptive metabolism of the different folate forms This is considered necessary for evaluating the adequacy of US RDA for folate [23], and for estimating potential risks from mandatory folic acid fortification, as a high intake of synthetic folic acid is suggested to accelerate the development of, e.g., colorectal cancer [24,25,26]
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