Supplement Forms & Bioavailability

Glycinate (bisglycinate): ~80% absorption. Chelated with glycine, which itself has calming properties. Minimal GI side effects. Best general-purpose form for deficiency correction and sleep support.

Citrate: ~30% absorption. Mild laxative effect. Useful if constipation is concurrent. More affordable than glycinate.

Threonate (Magtein): Uniquely crosses the blood-brain barrier. Research shows improved cognitive function and synaptic density. Best for cognitive/neurological use but expensive and low elemental magnesium per dose.

Oxide: ~4% absorption. Essentially a laxative at supplement doses. Found in most cheap multivitamins and marketed by dose (400mg!) while delivering almost nothing. The go-to example of how form matters more than dose.

Taurate: Chelated with taurine. Preliminary evidence for cardiovascular and blood pressure support. Reasonable absorption.

Methylfolate (5-MTHF, L-methylfolate): The bioactive form. Bypasses the MTHFR enzyme entirely. ~40-60% of the population has at least one MTHFR polymorphism reducing folic acid conversion. Methylfolate works regardless of genetics.

Folic acid (synthetic): Requires 4 enzymatic conversion steps to become usable. Unmetabolized folic acid (UMFA) accumulates in the bloodstream at doses above ~200 mcg and may mask B12 deficiency, with preliminary associations to colorectal cancer risk at chronic high doses. Still used in most fortified foods and cheap supplements.

Folinic acid (calcium folinate): An intermediate form that bypasses the MTHFR step but still requires one more conversion. Sometimes preferred in specific clinical protocols.

Methylcobalamin: Bioactive coenzyme form. Used directly in methionine synthase for homocysteine recycling. No conversion needed. Light-sensitive and less stable in supplements, so storage matters.

Adenosylcobalamin: The other bioactive form. Used in mitochondrial energy production. Less common in supplements but important for complete B12 status.

Hydroxocobalamin: Precursor that converts to both active forms. Longer retention time in the body. Used in B12 injections and preferred by some practitioners.

Cyanocobalamin: Synthetic form bound to cyanide (trace amounts, not dangerous). Requires removal of the cyanide group plus conversion to active form. Cheapest and most stable. Adequate for most people but inferior for those with impaired conversion pathways.

Iron bisglycinate (Ferrochel): Chelated amino acid form. Absorbed via peptide transporters, not the same pathway as standard iron salts. 2-4x better absorption than sulfate with significantly fewer GI side effects (nausea, constipation, dark stools).

Ferrous sulfate: The medical standard. Cheap and well-studied. Effective but notorious for causing constipation, nausea, and stomach pain. Absorption improves with vitamin C, decreases with food (but food reduces side effects -- a frustrating trade-off).

Ferrous fumarate: Higher elemental iron per dose than sulfate. Similar side effect profile. Common in prescription iron supplements.

Carbonyl iron: Elemental iron particles. Slower absorption, lower overdose risk. Sometimes preferred for pediatric safety.

Zinc picolinate: Chelated with picolinic acid. Some research shows superior absorption vs gluconate and citrate. The form most commonly recommended by integrative practitioners.

Zinc bisglycinate: Well absorbed, gentle. Good alternative to picolinate.

Zinc gluconate: Common in lozenges (zinc for colds research mostly used this form). Decent absorption, affordable.

Zinc oxide: Poorly absorbed (~50% less than picolinate). Common in cheap supplements and sunscreen. Not recommended for correcting deficiency.