What are the best dietary sources of folic acid?

In 1941, around four tonnes of spinach were used to isolate a small amount of folates. The compound discovered was named folic acid, from the Latin word *folium*, meaning "leaf". It was not until subsequent years that its chemical structure was precisely determined and a method for its synthesis was developed. Spinach remains an important source of vitamin B9, although other everyday foods also contain significant amounts of folates. Pregnant women, amongst others, should pay particular attention to the level of this compound in their diet.

1. Characteristics of folic acid
2. Folic acid intake guidelines
3. Sources of folic acid
4. FAQ

Characteristics of folic acid

Vitamin B9 comprises a group of compounds known as folates. Their natural forms are found in food, whilst folic acid is a synthetic and more stable form of vitamin B9, used mainly in dietary supplements and fortified products. Vitamin B9 is water-soluble and should therefore be consumed regularly as part of the diet.

Natural folates are sensitive to heat, light and oxygen, and their content in foods may decrease during prolonged storage, repeated reheating and cooking in large quantities of water.

Once absorbed, folates are converted into active forms that participate in reactions involving the transfer of one-carbon units. These processes are necessary for the formation of DNA and RNA and for the metabolism of certain amino acids. According to authorised health claims, folates contribute to normal amino acid synthesis and play a role in cell division. An adequate intake is particularly important for tissues in which cells divide and regenerate rapidly.

Folic acid intake guidelines

The European Food Safety Authority (EFSA) has set the average requirement for healthy adults at 250 µg of folate equivalents (DFE) per day, and the population reference intake at 330 µg DFE. During pregnancy, EFSA recommends 600 µg DFE per day, and 500 µg DFE during breastfeeding. DFE equivalents take into account differences in the absorption of the various forms of this vitamin. 1 µg of natural folates present in food corresponds to 1 µg DFE, whilst 1 µg of synthetic folic acid from a supplement or fortified product, consumed with a meal, corresponds to approximately 1.7 µg DFE.

Estimated folic acid content in selected sources

Sources of folic acid

Key sources

The richest natural sources of folate are liver (beef, pork, poultry), pulses (e.g. soya) and dark green vegetables. Half a glass of cooked spinach provides around 131 µg DFE; the same portion of cooked black-eyed beans around 105 µg; four cooked asparagus spears around 89 µg; half a glass of Brussels sprouts around 78 µg; half a glass of avocado around 59 µg; and half a glass of cooked broccoli around 52 µg.

Other foods

Daily sources can also include lentils, chickpeas, beans, romaine lettuce, green peas, wheatgrass, oranges, peanuts and eggs. Pulses can be added regularly to soups, salads, sandwich spreads and one-pot dishes, whilst spinach, broccoli and asparagus are best steamed briefly, blanched or eaten in dishes that also use the cooking liquid. Avocados, lettuces and citrus fruits do not require heat treatment, so they make it easier to increase your intake of folate without any losses associated with heating.

Specific recommendations

For most healthy people, a varied diet should form the basis of their intake. A notable exception is the period when planning a pregnancy: the WHO recommends taking 400 µg of folic acid daily from the start of trying for a baby until the end of the 12th week of pregnancy. Higher doses should only be taken following medical advice. In adults, the upper tolerable level for long-term intake of folic acid and authorised forms of 5-MTHF (calcium methylfolate) from supplements and fortified foods is 1,000 µg per day. Importantly, this limit does not apply to natural folates present in unprocessed foods.

"The best source of folates is a varied diet rich in green leafy vegetables, pulses and other plant-based foods. Folic acid supplementation is particularly important, above all, for women planning a pregnancy and during early pregnancy, in accordance with current recommendations." Anna Zięba – Dietitian

FAQ

Are folic acid and folates the same thing?

Not exactly. Folates are the natural forms of vitamin B9 found in food, whilst folic acid is its synthetic, more stable form used in dietary supplements and fortified products.

Does cooking reduce the folate content?

Yes. Natural folates are sensitive to high temperatures and are easily leached into the water during cooking. It is therefore advisable to cook vegetables briefly, preferably by steaming, or to use the water left over from cooking to prepare dishes.

Who should take particular care to ensure an adequate intake of folate?

An adequate intake of vitamin B9 is important for everyone, but it is particularly important for women planning a pregnancy and during early pregnancy, when the need for folate increases significantly.

Does diet alone always meet the body’s folic acid requirements?

For most healthy people, a well-balanced diet can provide an adequate amount of folate. The exception is women planning a pregnancy and pregnant women, for whom folic acid supplementation is recommended in accordance with guidelines.

Is it possible to take too much folic acid?

Yes. The tolerable upper intake level for synthetic folic acid and authorised forms of 5-MTHF from supplements and fortified foods is 1,000 µg per day for adults. This limit does not apply to natural folates from food.

Are fruits a good source of folates?

Yes, although they usually contain less than leafy vegetables and pulses. The best sources include, in particular, oranges, grapefruit, avocados and certain berries.

Sources:

• Lan, X., Field, M. S., & Stover, P. J. (2018). Cell cycle regulation of folate-mediated one-carbon metabolism. Wiley interdisciplinary reviews. Systems biology and medicine, 10(6), e1426. https://doi.org/10.1002/wsbm.1426
• Suitor, C. W., & Bailey, L. B. (2000). Dietary folate equivalents: interpretation and application. Journal of the American Dietetic Association, 100(1), 88–94. https://doi.org/10.1016/S0002-8223(00)00027-4
• Viswanathan, M., Urrutia, R. P., Hudson, K. N., Middleton, J. C., & Kahwati, L. C. (2023). Folic Acid Supplementation to Prevent Neural Tube Defects: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA, 330(5), 460–466. https://doi.org/10.1001/jama.2023.9864