B3+.

About sixty milligrams of dietary tryptophan yields one milligram of niacin equivalents through the kynurenine pathway, which is why intake is expressed in niacin equivalents. Tryptophan status therefore sets part of the body's own B3 supply.

Converting tryptophan to the niacin ring requires kynureninase, which depends on pyridoxal-5-phosphate. Low B6 status stalls that step and shunts intermediates down the xanthurenic acid branch instead.

The hydroxylation step in the tryptophan to niacin route uses a flavin adenine dinucleotide enzyme built from riboflavin. Riboflavin status therefore gates how much niacin the body makes for itself.

Tryptophan 2,3-dioxygenase and indoleamine dioxygenase are heme-containing enzymes that open the indole ring, the committed first step toward niacin. Iron status therefore sits upstream of endogenous niacin formation.

A large leucine excess inhibits quinolinate phosphoribosyltransferase and lowers the yield of niacin from tryptophan, the classic explanation for niacin shortfall on leucine-heavy grain diets. It is a competitive effect on one pathway step.

Nicotinamide N-methyltransferase disposes of excess nicotinamide by attaching a methyl group taken from S-adenosylmethionine. Trimethylglycine restores that methyl pool by remethylating homocysteine, which is why the two are formulated together at higher B3 intakes.

Each nicotinamide molecule methylated draws one methyl group from S-adenosylmethionine, so sustained high B3 intake taxes SAM directly. The relationship runs in both directions on the same methyl budget.

5-methyltetrahydrofolate donates the methyl group that remethylates homocysteine back to methionine and then to SAM. That is the same SAM pool nicotinamide methylation consumes, so folate status buffers a high B3 intake.

Methionine synthase needs cobalamin to move the methyl group from folate onto homocysteine and regenerate SAM. Without it the methyl pool that clears nicotinamide is not refilled.

One of the main routes for disposing of nicotinic acid is conjugation with glycine to form nicotinuric acid. Glycine availability therefore participates in how a nicotinic acid dose is cleared.

Niacin enters NAD synthesis through the Preiss-Handler route while nicotinamide riboside enters via nicotinamide riboside kinase. They converge on the same coenzyme, so stacking them raises one pool rather than two.

NMN is one enzymatic step from NAD and niacin reaches the same molecule through the Preiss-Handler route. Both are precursors of one coenzyme and their effects overlap rather than add.

Nicotinic acid and nicotinamide both build NAD, but only nicotinic acid activates the HCA2 receptor on skin and fat cells that produces flushing and the lipid effects. Choosing between them is a choice of which extra action you want, not of vitamin potency.

Inositol hexanicotinate is six nicotinic acid molecules esterified to inositol, hydrolysed slowly so free nicotinic acid appears gradually and flushing is muted. It is the same vitamin delivered on a different release curve.

Glucose tolerance factor chromium is manufactured by binding chromium to nicotinic acid, and the niacin ligand is what makes the chromium biologically active in that complex. The pairing is chemical, not incidental.

Nicotinamide, the amide form of B3, binds the sirtuin catalytic site and blocks the deacetylation reaction that resveratrol is taken to encourage. Large nicotinamide loads therefore pull against a sirtuin-directed formula, while nicotinic acid raising NAD pulls with it.

Nicotinic acid acts on hepatic lipoprotein assembly and fatty acid release from fat cells while monacolin K acts on cholesterol synthesis, so their effects on normal blood lipid levels add. The combination also stacks the muscle and liver monitoring considerations of both.

The nicotinic acid flush is produced by prostaglandin D2 released from skin cells, and salicylates dampen it by inhibiting prostaglandin formation. White willow supplies salicin, a slower and weaker salicylate source than aspirin.

NADH is the reduced state of the same dinucleotide that niacin supplies the ring for, so both act on one coenzyme pool. They overlap rather than complement.

Niacin builds NAD, which pairs with the flavin, thiamin and pantothenate coenzymes at consecutive steps of energy metabolism, and B6, B2 and folate also gate niacin's own formation from tryptophan. A complex covers those dependencies together.

NAD is assembled by ATP-dependent kinase and adenylyltransferase steps, and every one of those runs on Mg-ATP rather than free ATP. Magnesium is therefore a silent requirement of turning niacin into usable NAD. This is cofactor biochemistry rather than a supplement pairing anyone has trialled.

NAD and coenzyme A are the two carrier molecules that make oxidative metabolism run: CoA delivers acyl groups into the TCA cycle, NAD carries the electrons out of it. A shortfall in either stalls the same sequence at a different step. B-complex products carry both for that reason.

Glutathione reductase regenerates reduced glutathione using NADPH, which is made from the NADP pool that niacin supplies. Antioxidant capacity therefore depends on niacin status as well as on cysteine supply. This is settled redox biochemistry.

NAC supplies the cysteine that limits glutathione synthesis while the NADPH derived from niacin supplies the reducing power that keeps glutathione in its active form. The two address different constraints on the same system. Neither substitutes for the other.

Lipoic acid is the cofactor at the core of the pyruvate and alpha-ketoglutarate dehydrogenase complexes, and the reduced lipoamide it generates is re-oxidised by an NAD-dependent enzyme. The two cofactors work in the same catalytic cycle. Dihydrolipoic acid also participates in regenerating other antioxidants downstream.

Quercetin inhibits CD38, the ectoenzyme that is a major consumer of NAD in tissue, which is the rationale for pairing it with niacin-family precursors. The mechanism is described in cell and animal work. Whether it shifts human NAD levels at supplement doses has not been shown.

Apigenin is another flavonoid CD38 inhibitor, so it is combined with NAD precursors on the reasoning that slowing degradation complements raising supply. Support comes from laboratory and rodent work. Read it as mechanistic rather than clinical.

Pterostilbene is a sirtuin-activating stilbene and sirtuins are NAD-consuming enzymes, so raising NAD supply and stimulating the enzymes that spend it are paired deliberately in longevity-positioned formulas. The pairing appears in commercial products and in cell work. Human outcome data for the combination is limited.

Excess nicotinamide is cleared by nicotinamide N-methyltransferase, which spends a methyl group from SAM to make N1-methylnicotinamide. High nicotinamide intake therefore draws on the same methyl pool that methionine supplies. This is the reason methyl donors are commonly formulated alongside high-dose B3.

Alcohol dehydrogenase and several other zinc metalloenzymes use NAD as their electron acceptor, so both the metal and the cofactor are needed for the same reaction to proceed. The requirement is structural for zinc and catalytic for NAD. This is textbook enzymology.

Thiamine pyrophosphate is the cofactor for the decarboxylation step of pyruvate dehydrogenase and NAD is the electron acceptor two steps later in the same complex. A shortfall in either stops the conversion of pyruvate to acetyl-CoA. B-complex formulation reflects that they are consumed together.

NADPH from the niacin-derived NADP pool drives the enzymatic regeneration of ascorbate from its oxidised form. Ascorbate in turn recycles tocopherol. Niacin sits at the reducing end of that relay rather than in the antioxidant role itself.