Bisphenol A: the pathway in the body

This page shows the biochemical pathway behind the laboratory value Bisphenol A (BPA): 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

Bisphenol A (BPA) is an industrial chemical from polycarbonate plastics and can coatings that enters the body mainly through food. The liver quickly binds it to glucuronic acid and the kidneys excrete it within a day; in free form it can bind to oestrogen receptors.

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. Polycarbonate, resins → BPA in food migration with heat BPA enters the body mainly through food and drink. This is the main route of uptake. Source 1↑ supplies Food supplies most of the BPA that enters the body; dust and skin contact contribute less. observed in studies Source 1
   ⚖ When the balance tips

   too much — If more contaminated food is eaten, the amount excreted in the urine rises over the following hours.

   too little — If little of it is eaten, BPA in the urine falls within a day.

   observed in studies · Source 1, 2

2. BPA in food → Absorption in the gut BPA is almost completely absorbed in the gut and reaches the liver first with the portal blood. Source 2↑ supplies The route via the portal vein delivers BPA to the liver first, before it reaches the rest of the body. There most of it is bound at once. established physiology Source 2
   ⚖ When the balance tips

   too much — If much BPA arrives at once, the liver still binds most of it during the first pass.

   too little — If little arrives, correspondingly little BPA glucuronide forms.

   established physiology · Source 2

3. BPA in the liver → BPA glucuronide UGT2B15 · UDP-glucuronic acid BPA glucuronide is water-soluble and does not bind to oestrogen receptors. It enters the blood and from there the urine. Source 2, 1↓ depletes Binding to glucuronic acid removes the hormone-like action of BPA and makes it excretable via the kidneys. established physiology Source 1, 2
   ⚖ When the balance tips

   too much — If much BPA is bound, BPA glucuronide in the blood rises briefly and is excreted quickly.

   too little — If little is bound, more BPA stays free.

   established physiology · Source 2

4. BPA glucuronide → BPA in urine via the kidneys Almost all BPA leaves the body within a day as glucuronide in the urine. In the laboratory the bond is split and the total BPA is measured. Source 2↓ depletes The kidneys remove BPA glucuronide from the body promptly; the urine value therefore mainly reflects uptake over the last hours to days. established physiology Source 2
   ⚖ When the balance tips

   too much — If much BPA was absorbed recently, the amount in the urine rises; a few hours later it falls again.

   too little — If little was absorbed recently, little BPA is found in the urine, even if more was absorbed earlier.

   established physiology · Source 2

5. BPA in the liver → Free BPA in blood A small part of the BPA stays unbound in the blood. Only this free form can bind to hormone receptors. Source 2, 5↕ both, depending on amount Free BPA resembles oestradiol and can occupy its receptors; depending on tissue and amount it acts there as a stimulator or an inhibitor. observed in studies Source 5
   ⚖ When the balance tips

   too much — If there is more free BPA in the blood, more receptors are occupied.

   too little — If hardly any free BPA remains because the liver binds almost all of it, little reaches the receptors.

   observed in studies · Source 5, 2

6. Through the skin → Free BPA in blood A small part of the BPA stays unbound in the blood. Only this free form can bind to hormone receptors. Source 2, 5↕ both, depending on amount Free BPA resembles oestradiol and can occupy its receptors; depending on tissue and amount it acts there as a stimulator or an inhibitor. observed in studies Source 5
   ⚖ When the balance tips

   too much — If there is more free BPA in the blood, more receptors are occupied.

   too little — If hardly any free BPA remains because the liver binds almost all of it, little reaches the receptors.

   observed in studies · Source 5, 2

7. Free BPA in blood → Oestrogen receptors binding BPA binds to the oestrogen receptors ERα and ERβ in the cell nucleus and to GPER at the cell membrane, each time more weakly than oestradiol. Source 5↕ both, depending on amount Via the receptors, BPA can switch genes on and off and trigger rapid signals in the cell. In cell experiments the effect depends strongly on amount and cell type. observed in studies Source 5
   ⚖ When the balance tips

   too much — If much BPA is bound, it mimics oestradiol at the receptors or disturbs its signals.

   too little — If little is bound, the body's own hormones alone determine the signal.

   observed in studies · Source 5

   Field of research — The hormone-like action of BPA is studied in animal and population studies on reproduction. Source 7

Further stations

• Polycarbonate, resins — bottles, can linings Bisphenol A is a building block of polycarbonate plastics and epoxy resins, for example in the inner coatings of food cans. It used to be found in thermal paper as well. Source 1↑ supplies The bonds in the plastic are not fully stable: heat, acid and ageing release single BPA molecules, which pass into food. observed in studies Source 1
  ⚖ When the balance tips

  too much — If containers are heated or stored for a long time, more molecules pass into the contents.

  too little — If food hardly comes into contact with such materials, little BPA gets into it.

  observed in studies · Source 1

• Through the skin — e.g. thermal paper BPA can be absorbed through the skin from thermal paper, more so when the hands are greasy or wet with hand sanitiser. This route initially bypasses the liver. Source 4↑ supplies BPA absorbed through the skin reaches the blood without passing the liver first; a larger share is initially present there in unbound form. observed in studies Source 4
  ⚖ When the balance tips

  too much — If thermal paper is handled with wet hands, free BPA in the blood rises more than with the same amount from food.

  too little — Without such skin contact, BPA in the body comes almost entirely from food.

  observed in studies · Source 4

• BPA in the liver — first pass In the liver cell, BPA is bound to glucuronic acid, mainly by the enzyme UGT2B15. This requires UDP-glucuronic acid. Source 3↓ depletes During the first pass, the liver removes most of the absorbed BPA from the blood by binding it to glucuronic acid. established physiology Source 3, 2
  ⚖ When the balance tips

  too much — If BPA arrives faster than UGT2B15 can bind it, more free BPA reaches the circulation.

  too little — If variants of UGT2B15 work more slowly, BPA is bound more slowly in liver samples.

  observed in studies · Source 3

Cofactors in this pathway

• UDP-glucuronic acid — Supplies the sugar residue that UGT2B15 attaches to BPA, making it water-soluble and hormonally inactive Source 3
• NAD⁺ — Cofactor of UDP-glucose dehydrogenase, which forms UDP-glucuronic acid from UDP-glucose Source 6In the ORY catalogue as a laboratory value: NAD⁺ (Nicotinamidadenindinukleotid)
• Glucose — Starting material of UDP-glucuronic acid; the sugar residue for conjugation is made via UDP-glucose Source 6
• Oestradiol — The body's own partner of the oestrogen receptors to which free BPA also binds; oestradiol binds far more tightly Source 5In the ORY catalogue as a laboratory value: Estradiol (E2)

Sources

1. Vandenberg LN, Hauser R, Marcus M et al. Human exposure to bisphenol A (BPA). Reprod Toxicol 2007 · PubMed 17825522
2. Völkel W, Colnot T, Csanády GA et al. Metabolism and kinetics of bisphenol a in humans at low doses following oral administration. Chem Res Toxicol 2002 · PubMed 12387626
3. Street CM, Zhu Z, Finel M et al. Bisphenol-A glucuronidation in human liver and breast: identification of UDP-glucuronosyltransferases (UGTs) and influence of genetic polymorphisms. Xenobiotica 2017 · PubMed 26999266
4. Hormann AM, Vom Saal FS, Nagel SC et al. Holding thermal receipt paper and eating food after using hand sanitizer results in high serum bioactive and urine total levels of bisphenol A (BPA). PLoS One 2014 · PubMed 25337790
5. Acconcia F, Pallottini V, Marino M. Molecular Mechanisms of Action of BPA. Dose Response 2015 · PubMed 26740804
6. Egger S, Chaikuad A, Kavanagh KL et al. UDP-glucose dehydrogenase: structure and function of a potential drug target. Biochem Soc Trans 2010 · PubMed 20863317
7. Siracusa JS, Yin L, Measel E et al. Effects of bisphenol A and its analogs on reproductive health: A mini review. Reprod Toxicol 2018 · PubMed 29925041

As of 2026-10-05. Draft written by Claude to schema v2; sources checked in PubMed; expert approval pending
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