Vitamin E: the pathway in the body · Biomarker & Blood Analysis

This page shows the biochemical pathway behind the laboratory value Vitamin E (tocopherol): which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Vitamin E is the collective name for eight fat-soluble compounds, of which alpha-tocopherol is the most abundant in blood. In cell membranes it stops chain reactions of fatty acid radicals. What the liver does not keep in circulation, it breaks down via CYP4F2 to soluble CEHC.

The pathway step by step

Each station states what the compound does there. Three signs: ↑ supplies — builds up or makes available · ↓ depletes — inhibits, consumes or withholds · ↕ both, depending on amount. Behind it stands what the statement rests on: established physiology, observed in studies, or contested. The signs do not grade; they name the direction.

1. Vitamin E in food → Micelles in small bowel Lipases, esterases · Bile acids Bile acids and fat-splitting enzymes from the pancreas break down dietary fats. In the process, vitamin E moves into small fat droplets called micelles. Without bile acids, most vitamin E stays in the gut contents. Source 1↑ supplies Micelles make the fat-soluble vitamin E reachable in the watery gut contents in the first place: they carry it to the surface of the gut cell. established physiology Source 1
   ⚖ When the balance tips

   too much — If many micelles with plenty of fat are present, more vitamin E reaches the gut cell; absorption depends strongly on how much fat arrives at the same time.

   too little — If few bile acids or lipases arrive, fewer micelles form; vitamin E then largely stays in the gut contents and leaves with the stool.

   established physiology · Source 1

2. Micelles in small bowel → Into the gut cell NPC1L1, SR-BI Transport proteins in the surface of the gut cell, including NPC1L1 and SR-BI, absorb vitamin E from the micelles. The same transporters also absorb cholesterol. Source 1↑ supplies NPC1L1 and SR-BI bring vitamin E into the gut cell. They hardly distinguish between the forms and also absorb cholesterol and other fat-soluble substances. established physiology Source 1
   ⚖ When the balance tips

   too much — If many other fat-soluble substances arrive at the same time, such as cholesterol or carotenoids, they share the same transporters with vitamin E.

   too little — If the transporters work less, less vitamin E enters the gut cell; part of it also passes through the membrane without a transporter.

   observed in studies · Source 1

3. Into the gut cell → Chylomicrons · Dietary fats The gut cell packs vitamin E together with fats into chylomicrons. These reach the blood via the lymph, and their remnants travel on to the liver. On the way they release part of it to tissues. Source 1↑ supplies Chylomicrons carry all forms of vitamin E equally. Where lipoprotein lipase releases fat from them, for example in muscle and adipose tissue, vitamin E also passes into these tissues. established physiology Source 1
   ⚖ When the balance tips

   too much — If there is a lot of vitamin E in the chylomicrons, they release more to tissues on the way, and more reaches the liver with the remnants.

   too little — If few chylomicrons are formed, for example because little fat arrives, correspondingly less vitamin E passes from the gut cell into lymph and blood.

   established physiology · Source 1

4. Chylomicrons → α-Tocopherol in VLDL α-TTP In the liver, α-tocopherol transfer protein (α-TTP) selectively picks out α-tocopherol and passes it to VLDL. The other forms are preferentially broken down, so α-tocopherol is the most common form in blood. What α-TTP does not pass on goes into breakdown. Source 2, 1↑ supplies α-TTP is the bottleneck: it selects α-tocopherol and passes it to VLDL, which carries it to the tissues. The other forms stay in the liver and are broken down. established physiology Source 2, 1
   ⚖ When the balance tips

   too much — If α-TTP is saturated, the liver releases no more α-tocopherol to VLDL; the excess goes into breakdown via CYP4F2 and into the bile.

   too little — If α-TTP works little, hardly any α-tocopherol leaves the liver; it is broken down there quickly, and little reaches blood and tissues.

   established physiology · Source 2, 5

5. Lipid peroxyl radical → Lipid hydroperoxide α-Tocopherol gives its hydrogen atom to the peroxyl radical; this becomes a lipid hydroperoxide, and the chain reaction stops. A tocopheroxyl radical remains, which vitamin C can convert back. Peroxidases then convert it. Source 3↕ both, depending on amount With the hydroperoxide the chain is broken, but it is still reactive: selenium-containing glutathione peroxidases convert it with glutathione into an alcohol. established physiology Source 3, 7
   ⚖ When the balance tips

   too much — If lipid hydroperoxide builds up, for example when little glutathione is available, it can break down into new radicals and start another chain.

   too little — If little lipid hydroperoxide arises, the glutathione peroxidases have little to convert and use up little glutathione.

   established physiology · Source 7

6. α-Tocopherol → 13'-Hydroxychromanol CYP4F2 · NADPH, Oxygen In the liver, the enzyme CYP4F2 attaches an OH group to the end of the long side chain. This starts the breakdown of the tocopherols. It breaks down other vitamin E forms faster than α-tocopherol. Source 5, 4↓ depletes CYP4F2 breaks down γ-tocopherol and the tocotrienols faster than α-tocopherol. α-Tocopherol thus stays in the body longer, while the other forms disappear quickly. established physiology Source 5, 4
   ⚖ When the balance tips

   too much — If a lot of vitamin E arrives, more of it is broken down via CYP4F2. The same enzyme also breaks down vitamin K at its side chain; this shared use is described as an interaction.

   too little — If CYP4F2 works more slowly, tocopherols and tocotrienols are broken down more slowly; in animal models they then stay in circulation longer.

   observed in studies · Source 4, 5

7. 13'-Hydroxychromanol → 13'-Carboxychromanol Dehydrogenases Dehydrogenases turn the OH group into an acid group. The side chain is thus ready for further breakdown. In cell culture these intermediates themselves act on enzymes. Source 4, 5↓ depletes The acid group prepares the side chain for shortening. In cell culture these long-chain intermediates themselves inhibit enzymes, such as those that make inflammatory messengers. observed in studies Source 4
   ⚖ When the balance tips

   too much — If 13'-carboxychromanol builds up, part of it passes unshortened via the bile into the stool.

   too little — If little 13'-carboxychromanol forms, the subsequent shortening to CEHC also runs more slowly.

   observed in studies · Source 4

8. 13'-Carboxychromanol → α-CEHC β-oxidation The side chain is shortened step by step (β-oxidation), leaving α-CEHC. This water-soluble compound is linked to sulphate or glucuronic acid and excreted via urine and bile. Its amount rises with vitamin E intake. Source 4↓ depletes α-CEHC is the end of the route: water-soluble, conjugated and excretable. By this route vitamin E leaves the body that the liver does not keep in circulation. established physiology Source 4, 5
   ⚖ When the balance tips

   too much — If vitamin E intake rises, more α-CEHC appears in the urine; in this way the body removes what α-TTP does not pass on.

   too little — If little vitamin E arrives, little is broken down to CEHC, and α-tocopherol stays in circulation longer.

   established physiology · Source 4, 5

Further stations

• Vitamin E in food — tocopherols, tocotrienols Vitamin E is the collective name for eight fat-soluble compounds: four tocopherols and four tocotrienols. They are found mainly in vegetable oils, nuts and seeds. They are absorbed only together with fat. Source 1↑ supplies Food supplies all eight forms. They are absorbed only together with fat; how much of them stays in the body is decided later by the liver. established physiology Source 1
  ⚖ When the balance tips

  too much — If a lot of vitamin E arrives, part of it is not absorbed; what the liver does not pass on as α-tocopherol is broken down and excreted.

  too little — If little vitamin E arrives, the liver keeps the available α-tocopherol in circulation via α-TTP and passes it to VLDL again and again.

  established physiology · Source 1, 2

• α-Tocopherol — in cell membranes In membranes, α-tocopherol sits between the fatty acids. Its ring part carries an OH group that can donate a hydrogen atom. In this way it interrupts lipid peroxidation in the membrane. Source 3↑ supplies α-Tocopherol gives its hydrogen atom to lipid peroxyl radicals and thus interrupts lipid peroxidation in membranes; the polyunsaturated fatty acids remain unchanged. established physiology Source 3
  ⚖ When the balance tips

  too much — If there is a lot of α-tocopherol and little vitamin C, more tocopheroxyl radicals remain; in laboratory experiments they then attack fatty acids themselves.

  too little — If there is little α-tocopherol in the membrane, chain reactions of lipid peroxidation run longer before they stop, and more fatty acids are altered.

  observed in studies · Source 3

• Lipid peroxyl radical — in the membrane When oxygen radicals meet polyunsaturated fatty acids, lipid peroxyl radicals form. They attack the next fatty acid – a chain reaction begins. α-Tocopherol intercepts them and is used up in the process. Source 3↓ depletes Peroxyl radicals alter polyunsaturated fatty acids in the membrane and create new radicals in the process. They are intercepted by α-tocopherol, which is used up in the process. established physiology Source 3
  ⚖ When the balance tips

  too much — If more peroxyl radicals form than α-tocopherol can intercept, α-tocopherol is used up, and the chain runs longer through the membrane.

  too little — If few peroxyl radicals form, α-tocopherol remains in the membrane longer and is hardly used up.

  established physiology · Source 3

Cofactors in this pathway

• Vitamin C — Converts the tocopheroxyl radical back into alpha-tocopherol; so it is available in the membrane again Source 3In the ORY catalogue as a laboratory value: Vitamin C (Ascorbinsäure)
• Bile acids — Form micelles with dietary fats from which the gut cell absorbs vitamin E; without them, little is absorbed Source 1In the ORY catalogue as a laboratory value: Gallensäuren (Stuhl)
• Selenium — Component of glutathione peroxidases, which further convert lipid hydroperoxides; this yields an alcohol Source 7In the ORY catalogue as a laboratory value: Selen
• Glutathione — Supplies glutathione peroxidases with the electrons for this; in doing so it is itself oxidised Source 7In the ORY catalogue as a laboratory value: Glutathion (GSH)
• NADPH — Supplies CYP4F2 with the electrons for the first breakdown step; without NADPH this step stops Source 5

What acts on this pathway

• Orlistat — Orlistat inhibits the fat-splitting lipases in the gut. Review articles describe that fat-soluble vitamins from food are then also absorbed to a lesser extent. Source 6

Sources

1. Rigotti A. Absorption, transport, and tissue delivery of vitamin E. Mol Aspects Med 2007 · PubMed 17320165
2. Arai H, Kono N. α-Tocopherol transfer protein (α-TTP). Free Radic Biol Med 2021 · PubMed 34563650
3. Traber MG, Atkinson J. Vitamin E, antioxidant and nothing more. Free Radic Biol Med 2007 · PubMed 17561088
4. Schmölz L, Birringer M, Lorkowski S et al. Complexity of vitamin E metabolism. World J Biol Chem 2016 · PubMed 26981194
5. Parker RS, Sontag TJ, Swanson JE et al. Discovery, characterization, and significance of the cytochrome P450 omega-hydroxylase pathway of vitamin E catabolism. Ann N Y Acad Sci 2004 · PubMed 15753130
6. Filippatos TD, Derdemezis CS, Gazi IF et al. Orlistat-associated adverse effects and drug interactions: a critical review. Drug Saf 2008 · PubMed 18095746
7. Jomova K, Alomar SY, Alwasel SH et al. Several lines of antioxidant defense against oxidative stress: antioxidant enzymes, nanomaterials with multiple enzyme-mimicking activities, and low-molecular-weight antioxidants. Arch Toxicol 2024 · PubMed 38483584

Related pathways

• APOE — chylomicrons
• Cholesterol and lipoproteins — chylomicrons
• Trans fatty acids — chylomicrons
• Triglycerides — chylomicrons
• Vitamin A — chylomicrons

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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