Folato y ácido fólico: por qué esta vitamina es tan importante

El folato se encuentra naturalmente en los alimentos, mientras que el ácido fólico es la forma sintética utilizada en suplementos y alimentos enriquecidos. El ácido fólico es absorbido más eficazmente por el organismo.

Las verduras de hoja verde oscura (espinacas, lechuga romana), legumbres, aguacate, espárragos y cítricos son ricas en folato. Los productos de cereales enriquecidos también son fuentes importantes.

Las mujeres embarazadas (o que planean estarlo) tienen una mayor necesidad. La dosis diaria recomendada sube de 400 µg a 600 µg. Se recomiendan suplementos de ácido fólico antes de la concepción.

Una deficiencia de folato puede provocar anemia y, en embarazadas, defectos del tubo neural en el bebé. Una sobredosis de alimentos es poco probable, pero posible con suplementos.

The evidence linking folate status to neural tube defect prevention is among the most robust in nutritional epidemiology. The landmark MRC Vitamin Study, published in 1991, demonstrated that supplementation with 4mg of folic acid in women at high risk of neural tube defect recurrence reduced incidence by 72%. Subsequent studies in general populations confirmed that daily supplementation with 400mcg reduces the risk of first-time neural tube defects by approximately 50–70%. Because neural tube closure is complete by day 28 of embryonic development — before most women realise they are pregnant — current guidelines in most countries recommend that all women who could become pregnant take 400mcg of folic acid daily, or consume equivalent amounts through fortified foods. Women with a previous neural tube defect-affected pregnancy, those with the MTHFR TT genotype, those taking anti-epileptic medications that interfere with folate metabolism, or those with diabetes or obesity are typically recommended higher doses of 4–5mg daily under medical supervision. Beyond neural tube defects, higher folate intake during pregnancy is associated with reduced risks of cleft palate, congenital heart defects, and preterm birth in observational studies. Adequate folate also supports placental development and the extraordinary cell division demands of the first trimester. Some researchers argue that the current population recommendation of 400mcg may be insufficient for women with impaired folate metabolism and that 5-MTHF at comparable doses may be a more appropriate universal recommendation, particularly given the MTHFR variant prevalence. This remains an area of active scientific debate.

The supplement market offers several forms of vitamin B9: folic acid (the conventional synthetic form), folinic acid (5-formyltetrahydrofolate, also called leucovorin), and methylfolate (5-methyltetrahydrofolate or 5-MTHF), the latter sold under brand names including Metafolin and Quatrefolic. For the general population without known MTHFR variants, standard folic acid at 400mcg daily remains the evidence-based recommendation during reproductive years, supported by decades of safety and efficacy data. Concerns about UMFA at this dose are theoretically plausible but not yet demonstrated to cause measurable harm in most people. For those with MTHFR C677T homozygosity or with a personal or family history of neural tube defects, methylfolate (5-MTHF) is a logical choice: it bypasses the rate-limiting enzymatic step, does not produce UMFA, and is available in supplements ranging from 400mcg to 15mg. Starting at standard doses (400–800mcg) and increasing only under guidance is prudent, as some people with severely impaired methylation report paradoxical reactions to high-dose methylfolate. Folinic acid is sometimes used as an intermediate option for those who react to methylfolate. B-complex supplements typically provide folic acid; those wishing to switch to methylfolate need to specifically seek formulations listing 5-MTHF or methylfolate. For most people eating diets rich in legumes, leafy greens, and fortified foods, supplementation may be unnecessary outside pregnancy and conception planning — but given the prevalence of suboptimal intake in Western diets, a standard multivitamin containing 400mcg of folate is a reasonable low-risk insurance policy for most adults.