Form

The folate intermediate MTHFR reduces. It is also the form used to build thymidine for DNA.

Plant pigment the body converts to retinol as needed. Conversion is inefficient and varies a lot between people, and it needs fat in the meal to be absorbed at all.

Docosahexaenoic acid. Structural fat of the retina and brain, and the form that matters most in pregnancy.

Eicosapentaenoic acid. The omega-3 most of the inflammation and triglyceride evidence is built on.

Iron bound inside haem, from meat, poultry and fish. Absorbed by its own transporter, so phytate and tannins barely touch it.

The long-chain menaquinone used in most supplements. Half-life measured in days rather than hours, so one daily dose holds a steady level.

The circulating, active folate. MTHFR is the enzyme that makes it, so a slow MTHFR variant shows up as low 5-MTHF and high homocysteine.

Iron from plants and fortified foods. Absorbed through DMT1 in the ferrous state, so it is the form vitamin C rescues and the form phytate, tannins and calcium block.

The B12-shaped molecule in most algae and some fermented foods. It registers on some assays and does nothing in humans, so it is tracked separately rather than counted as B12.

The active coenzyme form of B6. This is what the enzyme actually binds, which is why supplements are often sold as P5P rather than pyridoxine.

Preformed vitamin A from animal foods. Ready to use, and the form that accumulates to toxicity if overdosed.

The menaquinone family, from fermented food and animal tissue. Longer-lived in blood than K1 and more active on bone and artery proteins.