Vitamin B9 (folate / folic acid)
A water-soluble vitamin essential for DNA synthesis, cell division and the formation of red blood cells, crucial in early pregnancy to prevent birth defects.
Vitamin B9 exists in a natural form (folate, in food) and a synthetic form (folic acid, in supplements and fortified foods). It is essential for DNA synthesis, cell division, the formation of red blood cells and the metabolism of homocysteine.
The original angle (pregnancy and the neural tube): the best-known role of B9 is the prevention of neural tube defects (spina bifida) in the embryo. A crucial and little-known point: the neural tube closes very early (days 21 to 28 of pregnancy), often before the woman even knows she is pregnant. This is why supplementation is recommended as soon as you plan a pregnancy (not when you discover it, which is often too late). It is one of the few supplements with strong consensus.
The folate vs folic acid debate: an important nuance: synthetic folic acid has to be converted by an enzyme (MTHFR) into active folate (methylfolate). Yet ~30 to 50% of the population carries a variation of the MTHFR gene that reduces this conversion. In these people, unmetabolised folic acid can build up, and some may benefit from active folates (methylfolate) rather than standard folic acid. The subject is debated but increasingly taken into account.
Beware of B12 masking: an excess of folic acid can mask a B12 deficiency (it corrects the anaemia but not the neurological damage of B12 deficiency, which progresses silently). Hence the importance of considering B9 and B12 together, especially in older people and vegans.
Fragility: natural folates are fragile: they are destroyed by prolonged cooking, light and storage. Raw or lightly cooked green vegetables keep more of them (“folate” comes from “foliage”, meaning leaf).
Sources: leafy green vegetables (spinach, lamb’s lettuce, watercress), pulses, liver, asparagus, broccoli, avocado, citrus fruit, eggs.