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 word folate itself derives from the Latin folium, meaning leaf, reflecting the fact that dark green leafy vegetables are the most concentrated food source of naturally occurring folate. Cooked spinach tops the list at approximately 263mcg DFE per 180g serving, followed closely by boiled lentils at 358mcg per cooked cup — making lentils one of the single richest folate sources available. Other legumes including black beans, chickpeas, kidney beans, and peas each provide 130–294mcg per cooked cup, making regular consumption of pulses one of the most effective dietary strategies for meeting folate needs. Asparagus provides around 134mcg per 90g serving, broccoli approximately 104mcg per 90g serving, and Brussels sprouts around 78mcg per 90g serving. Avocado is an unusually folate-rich fruit at around 122mcg per half fruit. Beetroot provides approximately 68mcg per 100g cooked. Citrus fruits — particularly orange juice — contribute meaningful amounts, with a glass of freshly squeezed orange juice providing around 75mcg. Liver is an exceptionally rich animal source at approximately 215mcg per 75g serving. Fortified breakfast cereals and breads contribute substantially to population folate intake in countries with mandatory fortification programmes — the US, Canada, Australia, and many others have required folic acid fortification of wheat flour since the late 1990s, significantly reducing rates of neural tube defects. Food folate is heat-sensitive and water-soluble: cooking methods that minimise water contact and heat exposure — steaming rather than boiling, using cooking water in sauces — preserve more folate.

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.

The guidance in this article draws on peer-reviewed nutrition and food-science literature as well as guidance from major public-health bodies. Key reference sources we have consulted while writing and updating this piece include:

• Harvard T.H. Chan School of Public Health, *The Nutrition Source*, 2024. • U.S. National Institutes of Health (NIH), Office of Dietary Supplements, fact sheets, 2024. • World Health Organization (WHO), Healthy Diet fact sheet, 2024. • Cochrane Database of Systematic Reviews — relevant systematic reviews, 2020–2024. • British Dietetic Association (BDA) Food Fact Sheets, 2024.

These references are provided so that motivated readers can verify claims and explore the underlying evidence directly. Where a specific trial, meta-analysis, or named author is referenced in the body of the article, that citation takes precedence over the general sources listed here. The article is reviewed periodically against newly published evidence and updated when meaningful new findings emerge.