Detox Guide · Alcohol and Liver Metabolism

Alcohol and the Liver: What Happens During Breakdown and How to Protect Your Liver

Every glass carries a metabolic price. It is paid in acetaldehyde, glutathione, NAD and B vitamins. Here you can see the bill.

SJ
Shukri Jarmoukli · Physician, Integrative Medicine
ViveCura Berlin
Mechanisms explained 23 verified sources Animal and human data kept apart
My starting point

I do not moralise about alcohol. I do not find the question of morality particularly interesting either.

What interests me is the bill. Every glass creates work in your liver, and that work is paid for in material. In coenzymes, in glutathione, in B vitamins, in time.

Once you know this bill, you make different decisions. Not out of a guilty conscience, but because you understand what is actually happening.

The evening was lovely. Why does the morning feel so expensive?

You had two, maybe three glasses. Nothing dramatic. No blackout, no drama.

And still: sleep was strange. You woke up at half past four and lay there. In the morning your head feels like cotton wool, concentration only arrives around eleven, and something in you is more irritable than usual.

Most people explain this with the word "hangover" and stop thinking there. That is understandable. But it misses the interesting part.

Because while you were sleeping, a shift was running in your liver that you never ordered. And that shift consumed material.

A change of perspective

For the body, alcohol is neither a nutrient nor a poison in the classical sense. It is a work order with the highest priority.

The liver cannot store ethanol and cannot simply excrete it. It has to convert it, immediately, and it pushes other work back to do so. Fat burning, new glucose production, detoxification of other substances. Everything moves one step down the queue.

That is not a weakness of the liver. That is its emergency programme. It is just not built to run several times a week.

And now let us look at how that shift actually runs.

What happens inside the liver cell, step by step

Breaking down alcohol is not a single reaction. There are at least three pathways running in parallel, and they contribute to different degrees depending on drinking habits.

1

Ethanol becomes acetaldehyde

In the cytosol of the liver cell sits alcohol dehydrogenase, ADH for short. It takes two hydrogen atoms off the ethanol. What remains is acetaldehyde. The hydrogen atoms land on a coenzyme called NAD, which thereby becomes NADH. Let us keep that point in mind, it becomes important in a moment.

2

Acetaldehyde becomes acetate

Acetaldehyde travels into the mitochondria, the power plants of the cell. There aldehyde dehydrogenase 2, ALDH2 for short, is waiting. It converts acetaldehyde into acetate, in other words acetic acid. Here too, NAD becomes NADH again.

3

Acetate leaves the liver

Acetate is comparatively harmless. It goes back into the blood and is burned in muscle, heart and other tissues into acetyl-CoA and finally into carbon dioxide and water. The lion's share of the calories from alcohol ends up here.

4

The second pathway: CYP2E1

With regular consumption, an enzyme in the endoplasmic reticulum is ramped up: cytochrome P450 2E1. It also breaks down ethanol, but with a side effect. In doing so it generates reactive oxygen species. These free radicals are the reason why regular drinking is biochemically something different from occasional drinking.

5

The third pathway: catalase

In the peroxisomes, catalase can oxidise ethanol with the help of hydrogen peroxide. In humans this pathway is considered quantitatively small, but it is mechanistically interesting because it shows how closely fat breakdown and alcohol breakdown are interlocked.

What the reviews showMechanism review

A research group around Song at the US institute for alcohol research systematically worked through the alcohol-metabolising enzymes. They describe that ADH, ALDH2 and CYP2E1 do not work independently, but influence one another.

Among the observations: ALDH2 can be inhibited in its function by various liver-toxic influences. When that happens, acetaldehyde and reactive fat breakdown products accumulate and can react with DNA, fats and proteins.

For you that means: the bottleneck is rarely at the first step. It is usually at the second, that is, at clearing away the intermediate product.

Song BJ, Akbar M, Jo I et al. Adv Pharmacol. 2015;74:303-372. DOI: 10.1016/bs.apha.2015.04.002
Why "I can handle a lot" is not a good sign

Alcohol dehydrogenase is already largely saturated at low blood concentrations. Breakdown therefore runs at an almost constant pace, regardless of how much more you drink. Roughly one standard drink per hour, with large individual variation.

When someone tolerates more over the years, that is often because CYP2E1 has been ramped up. This additional pathway clears more ethanol, but it pays for it with free radicals.

Greater tolerance is therefore not a sign of a more robust liver. It can be a sign that the more expensive breakdown pathway has taken over.

The NAD shift: why alcohol turns into liver fat

Now comes the part I find most fascinating, because it is so elegant and so consequential.

Imagine NAD as trays in a canteen. The kitchen needs empty trays to serve food. NAD is the empty tray. NADH is the full one.

Both alcohol breakdown steps take empty trays and hand back full ones. After two or three glasses, almost all the trays are suddenly full. The ratio of NADH to NAD shifts massively.

What the NADH shift slows down in metabolism

Fatty acid burning in the mitochondria slowed
Fat storage in the liver cell favoured
New glucose production from lactate and amino acids slowed

A simplified depiction of the direction, not of the exact magnitude. The bars show which pathways are slowed and which are favoured under an NADH shift.

Fat burning needs free NAD. It comes to a standstill. At the same time, alcohol breakdown produces building blocks from which the liver can build new fats. Together, both lead to fat being deposited in the liver cells.

That is alcoholic fatty liver, medically called steatosis. It does not hurt. It often shows up in no symptom at all. And in most people it is initially reversible.

How common this isReview article

An international research group around Seitz in Heidelberg compiled the state of knowledge on alcohol-related liver disease for Nature Reviews Disease Primers.

What was observed: most people who drink more than 40 grams of alcohol per day develop an alcoholic fatty liver. Only a portion of them progress to the more severe stages, meaning steatohepatitis, fibrosis and cirrhosis. Which genetic, epigenetic and non-genetic factors decide that is one of the open questions.

For you that means: 40 grams is roughly a litre of beer or half a bottle of wine per day. Fatty liver is the rule, not the exception. What comes after that varies greatly from person to person.

Seitz HK, Bataller R, Cortez-Pinto H et al. Nat Rev Dis Primers. 2018;4(1):16. DOI: 10.1038/s41572-018-0014-7
The mechanism in the animal modelIn vivo, mouse

A Chinese research group around Zhang investigated in 2025 how fat breakdown in the peroxisomes and alcohol breakdown are connected.

What was observed in mice: increased peroxisomal fatty acid breakdown supplies hydrogen peroxide, thereby accelerates ethanol oxidation and raises the mitochondrial NADH to NAD ratio. The consequence was slowed mitochondrial fat burning and an accumulation of triglycerides in the liver. Targeted inhibition of the peroxisomal pathway attenuated this fat deposition in fasting mice.

This is an animal model. In humans, this specific connection has not yet been conclusively proven. The direction does fit well with what we know from human physiology.

Zhang Y, Zhang W, Li Y et al. FASEB Bioadv. 2025;7(6):e70013. DOI: 10.1096/fba.2024-00211

Fatty liver is not a moral verdict. It is an accounting gap in the coenzyme budget.

And now you know why a fatty liver can develop even though someone hardly eats any fat.

Acetaldehyde: the substance that writes the bill

Ethanol itself is remarkably unreactive. It makes you drunk because it influences nerve cell membranes and receptors. But chemically it is a quiet fellow.

Acetaldehyde is not. Acetaldehyde is an aldehyde, and chemically speaking, aldehydes are Velcro. They bind to things they should not bind to.

What acetaldehyde can get hold of in the cell

  • DNA: It forms adducts, meaning chemical attachments to the building blocks of the genetic material. Best described is an adduct on guanine that can disturb DNA replication.
  • Proteins: It binds to the amino groups of proteins. If that changes the shape of an enzyme, its function can suffer.
  • The repair system of the cell nucleus: Review articles describe that acetaldehyde can inhibit nuclear DNA repair. That is exactly the system that should be clearing the adducts away again.
  • DNA methylation: The epigenetic labelling of genes can be disturbed. That is one route by which alcohol may leave traces even without direct DNA damage.
  • Vitamin B6 transport: More on that shortly, it deserves its own chapter.
Why alcohol is classified as carcinogenicReview article

In 2025, Seitz summarised the mechanisms between alcohol and tumours of the digestive tract in Zeitschrift für Gastroenterologie.

Described there: about 4 percent of all cancer cases worldwide are attributed to alcohol consumption. Acetaldehyde binds to DNA and proteins, inhibits oxidative defence and the repair system of the cell nucleus, and disturbs DNA methylation. In addition, reactive oxygen species arise via CYP2E1 and drive fat peroxidation. Its products, such as 4-hydroxynonenal and malondialdehyde, can in turn form DNA adducts. Interesting detail: microbes in the mouth and large intestine also produce acetaldehyde from ethanol.

For you that means: the cancer risk with alcohol is not a vague statistical artefact. There is a nameable chemical chain behind it.

Seitz HK. Z Gastroenterol. 2025;63(9):960-974. DOI: 10.1055/a-2588-6849

The flush reaction is a visible lab value

Some people turn bright red after half a glass. Palpitations, a feeling of warmth, sometimes nausea. Among friends, people laugh about it.

Biochemically, it is a finding. These people often carry a variant of the enzyme ALDH2 that works considerably more slowly. The first step runs normally, the second stalls. Acetaldehyde backs up and makes itself noticeable in the skin.

What that can mean in the long runReview article

A research group around Brooks at the US alcohol research institute reviewed the evidence on the flush reaction in PLoS Medicine in 2009.

Described there: people with this ALDH2 variant who nevertheless drink alcohol regularly carry a markedly increased risk of squamous cell carcinoma of the oesophagus. The authors argue that the flush reaction is an easily recognisable risk marker that is used far too rarely in counselling.

For you that means: if you turn red after little alcohol, that is a signal you can raise in a conversation with your doctor.

Brooks PJ, Enoch MA, Goldman D et al. PLoS Med. 2009;6(3):e50. DOI: 10.1371/journal.pmed.1000050
An honest assessment

These gene variants have been studied most often in East Asian populations. They also occur in other populations, but less frequently.

The reverse also holds: anyone who shows no flush reaction has no safety certificate. The bill simply runs more quietly then.

Glutathione: the fire water that gets used up along the way

Glutathione is a small molecule made of three amino acids: glutamate, cysteine and glycine. The bottleneck is almost always the cysteine, because it is the sulphur-containing one.

Think of glutathione as fire water. Wherever reactive oxygen species start small fires, they get put out. Afterwards the glutathione is oxidised and has to be regenerated or built anew.

During alcohol breakdown these fires arise in two places. Via CYP2E1 directly as free radicals. And indirectly via fat peroxidation, whose products are likewise defused via glutathione.

The glutathione pool in the mitochondriaMechanism review

Garcia-Ruiz and Fernandez-Checa in Barcelona studied the mitochondrial glutathione pool over many years and summarised it in a review.

Described there: mitochondria do not produce their own glutathione. They obtain it from the cytosol via a transporter. Under alcohol, the composition of the mitochondrial membrane changes, among other things through cholesterol, and becomes less fluid. Transport suffers, the mitochondrial glutathione pool falls. In models with alcohol-fed animals, this depletion alone was enough to make liver cells sensitive to the inflammatory messenger TNF.

For you that means: what matters is not the total pool in the blood, but where the glutathione sits. That is also the reason why lab values are only of limited use here.

Garcia-Ruiz C, Fernandez-Checa JC. J Gastroenterol Hepatol. 2006;21 Suppl 3:S3-S6. DOI: 10.1111/j.1440-1746.2006.04570.x
Important for everyday life

Glutathione is also the molecule the liver needs in order to catch a reactive intermediate product of paracetamol. This very intermediate arises via CYP2E1, that is, via the enzyme that alcohol upregulates.

In a specialist review, Rumack differentiates: at therapeutic doses he sees no increased risk even with alcohol consumption. With an overdose, by contrast, liver damage can turn out more severe with chronic alcohol consumption. He emphasises that CYP2E1 and glutathione must always be considered together and not separately.

The practical consequence belongs in a conversation with your doctor or your pharmacy. Please do not change dosages on your own.

A change of perspective

Many people think of detoxification as something you add. A tea, a powder, a cure.

From the perspective of cell biology, detoxification is above all a material problem. The liver has the tools. What can run out are the consumables: glutathione, sulphur, coenzymes, cofactors.

That is why the more interesting question is not "what do I take in addition", but "what am I currently using up faster than I am resupplying".

If you want to go deeper into this molecule, you will find the detailed account in our article on glutathione as a master antioxidant.

The B vitamin price: B1, B6 and folate

This is where it gets concrete, and this is where I see the biggest gap in the public discussion about alcohol.

A lot is said about liver values and little about the fact that alcohol burdens the household of three B vitamins in quite different ways.

Vitamin B1 · Thiamine

The active form thiamine pyrophosphate is a cofactor for three central enzymes of energy metabolism. Without them, the route from sugar into energy production stalls. With alcohol, several problems come together: lower intake, poorer absorption in the gut, disturbed conversion into the active form and reduced storage in the liver.

Vitamin B6 · Pyridoxal 5-phosphate

The active form is a cofactor for more than a hundred enzymes, among them many in amino acid and neurotransmitter metabolism. Acetaldehyde can displace it from its protein binding. Unbound, it is broken down faster.

Folate · Vitamin B9

Central for methylation, that is, for DNA synthesis, DNA stability and epigenetic regulation. Alcohol acts here at four points at once: less intake, poorer absorption, reduced storage in the liver, increased excretion via the urine.

Zinc

Not a B vitamin, but it belongs in the same bill. In advanced alcohol-related liver disease the zinc balance is regularly disturbed, among other things through lower intake, poorer absorption, increased excretion and altered transporters.

How acetaldehyde gets at vitamin B6In vitro, rat liver cells and human erythrocytes

In 1978, Lumeng published a series of laboratory experiments in the Journal of Clinical Investigation that still provide the standard explanation today.

What was observed: when acetaldehyde breakdown was inhibited, the pyridoxal 5-phosphate content in isolated liver cells fell by about 40 percent within 80 minutes. In dialysis experiments, acetaldehyde displaced the bound pyridoxal 5-phosphate from its binding proteins. In the presence of alkaline phosphatase, that accelerated its breakdown.

These are cell and tissue experiments, not a human study. They do, however, explain very plausibly why vitamin B6 comes out so reliably low with heavy alcohol consumption.

Lumeng L. J Clin Invest. 1978;62(2):286-293. DOI: 10.1172/JCI109128
Folate and liver diseaseReview article

Medici and Halsted at the University of California Davis worked through the connection between folate, alcohol and liver disease.

Described there: alcohol-related liver disease typically goes along with folate deficiency. It arises through lower intake, malabsorption in the gut, reduced uptake and storage in the liver and increased excretion via the urine. The deficiency interferes with methionine metabolism, with consequences for DNA synthesis, DNA stability and the epigenetic control of genes involved in liver damage.

For you that means: folate is no side detail in this topic. It sits at the interface between nutrient balance and the mechanisms through which alcohol leaves traces in the long run.

Medici V, Halsted CH. Mol Nutr Food Res. 2013;57(4):596-606. DOI: 10.1002/mnfr.201200077
Where it gets serious

A pronounced thiamine deficiency can lead to Wernicke encephalopathy, a neurological emergency with confusion, unsteady gait and eye muscle disturbances. Review articles emphasise that this picture is often recognised too late because it overlaps with other neurological conditions.

This is not a topic for self-treatment. Anyone who notices such symptoms, in themselves or in others, belongs in medical care without delay.

And now you know why, with alcohol, it is not only the liver values that are interesting, but also B1, B6, folate and zinc.

The hangover: what the data give us and what they do not

Now I have to qualify a widespread explanation that I myself long found convenient.

The story goes like this: the hangover is acetaldehyde. Full stop. It is catchy, it fits the biochemistry, and according to current data it is too simple.

What hangover research actually measuredReview article

A research group around Mackus at the University of Utrecht reviewed the studies on alcohol metabolism and hangover severity.

What was observed: blood ethanol concentration was directly related to hangover severity, whereas the acetaldehyde level was not to a statistically meaningful degree. People who broke down ethanol faster had milder hangovers. One possible explanation from the authors: ethanol crosses the blood-brain barrier, acetaldehyde essentially does not. For the markers of oxidative stress the picture was split: early values were negatively related to hangover severity, later values positively.

For you that means: a hangover is not one single toxin. It looks more like a sum of metabolic load, inflammatory signals and disturbed sleep.

Mackus M, van de Loo AJ, Garssen J et al. J Clin Med. 2020;9(11):3421. DOI: 10.3390/jcm9113421
The four most likely factorsReview article

A group around Palmer at Imperial College London set animal and human studies on the hangover side by side.

As the most likely contributors they name: the breakdown products of alcohol, changes in messenger substances in the brain with a particular eye on glutamate, inflammatory factors and mitochondrial dysfunction. They openly criticise that many hangover studies are methodologically weak, with differing amounts, time windows and measurement methods.

For you that means: if someone sells you a simple hangover formula, healthy scepticism is in order. Towards me as well.

Palmer E, Tyacke R, Sastre M et al. Alcohol Alcohol. 2019;54(3):196-203. DOI: 10.1093/alcalc/agz016

The underestimated part: sleep

Many people drink in the evening because they fall asleep faster. That is even true. It is just half the story.

What alcohol does to sleepReview article

Ebrahim and colleagues reviewed all known investigations into alcohol and night-time sleep in healthy people.

What was observed across all dosages: shorter time to fall asleep, a more stable first half of the night and more sleep interruptions in the second half. The onset of the first REM phase was clearly delayed at all dosages. At medium and high amounts, the REM share across the whole night fell. Deep sleep in the first half of the night increased in the majority of studies.

For you that means: waking up at half past four is neither coincidence nor weakness. It is a well documented shift in sleep architecture.

Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB. Alcohol Clin Exp Res. 2013;37(4):539-549. DOI: 10.1111/acer.12006
The reframe that explains the morning

A hangover is rarely a single cause. It looks more like a bottleneck in several places at once: a shifted coenzyme budget, consumed glutathione, an irritated immune system, fragmented sleep, fluid and electrolyte shifts.

That is also why no single trick works reliably. If you top up in one place while something is missing in four others, you notice little of it.

Who should look particularly closely here

Up to this point I have been talking about averages. Now it gets personal, because on this topic the differences between people are enormous.

Situations that belong in medical care

  • Pregnancy and wanting to conceive: For alcohol in pregnancy, no harmless amount is known. This is not an area for your own weighing up, it belongs in medical care.
  • Alcohol dependence or a suspicion of it: Withdrawal can become physically dangerous. Anyone who suspects they are dependent should not stop on their own, but get medical support. That is not a sign of weakness, but of prudence.
  • Existing liver disease: Fatty liver, hepatitis, fibrosis or elevated liver values change the whole calculation. This needs individual assessment.
  • Regular medication: Many active substances are metabolised via the same enzyme systems. Interactions belong in the pharmacy or the consulting room, not on the internet.
  • A pronounced flush reaction: A sign of a slower ALDH2 variant, which you can raise in a conversation with your doctor.
On the question of a safe amountOfficial document, WHO

The World Health Organization took a position on this in Lancet Public Health in 2023. Its core statement: for cancer risk, no threshold can be given below which the risk demonstrably falls away.

A population-based analysis by the International Agency for Research on Cancer for the year 2020 arrived at an estimated 741,300 new cancer cases worldwide attributed to alcohol consumption, that is 4.1 percent of all new cases. Most of them affected the oesophagus, the liver and the breast. Moderate consumption below 20 grams per day accounted for about 103,100 cases.

For you that does not mean every glass makes you ill. It means: there is no range that can honestly be called protected.

Anderson BO, Berdzuli N, Ilbawi A et al. Lancet Public Health. 2023;8(1):e6-e7. DOI: 10.1016/S2468-2667(22)00317-6 · Rumgay H et al. Lancet Oncol. 2021;22(8):1071-1080. DOI: 10.1016/S1470-2045(21)00279-5
How I handle this

I do not tell anyone that they may never drink a glass of wine again. That would be presumptuous and unrealistic in most people's lives.

What I consider honest: lay the bill open, do not talk the risk curve prettier than it is, and then look together at where your personal point lies. Between "never again" and "who cares" there are a great many possibilities.

What you can do in practical terms

Three levers, no more. Everything else is cosmetics as long as these three are not in place.

Lever 1: Reduce the amount, counted in days

Not in good intentions, but in calendar weeks. How many days per week are alcohol-free? That is a number you can answer tomorrow.

The reason is the kinetics. The liver works at an almost constant pace. So what counts is not only the total amount, but also how much recovery time lies between the loads.

What an alcohol-free month can shiftReal-world, prospective, n=141

A group around Mehta at University College London followed people who had committed to a month off alcohol and compared them with people who kept drinking.

What was observed in the abstinence group of 94 participants, with a baseline consumption of 258 grams per week on average: the HOMA index as a measure of insulin resistance fell by 25.9 percent, systolic blood pressure by 6.6 percent, body weight by 1.5 percent. Two cancer-associated growth factors fell by 41.8 and 73.9 percent. In the control group of 47 participants nothing meaningful changed. The changes did not hang on diet, exercise or smoking.

For you that means: this is an observational study without random allocation, so not proof of causality. But the magnitude and the speed are remarkable.

Mehta G, Macdonald S, Cronberg A et al. BMJ Open. 2018;8(5):e020673. DOI: 10.1136/bmjopen-2017-020673

Lever 2: Take the nutrient basis seriously, without treating it as a free pass

If alcohol burdens B1, B6, folate and zinc and consumes glutathione, then it makes sense not to live carelessly in exactly those areas.

Concretely that means: vegetables and legumes for folate. Eggs, meat and legumes as sources of sulphur-containing amino acids from which the body can build glutathione. Wholegrains and legumes for thiamine. And if a relevant deficiency is suspected, a laboratory measurement instead of guesswork.

I deliberately do not name dosages here. They depend on baseline values, kidney function, medication and goal, and they belong in individual advice.

Why supplements are no substituteRCT, double-blind, placebo-controlled, n=37

Medici and colleagues tested S-adenosylmethionine, a substance that helps regulate glutathione formation, in a double-blind study over 24 weeks in people with alcohol-related liver disease.

What was observed: the liver values AST, ALT and bilirubin improved in the group as a whole over the 24 weeks. Between verum and placebo, however, there was no difference, neither in the laboratory values nor in the liver tissue examination. The authors attribute the improvement to the required abstinence.

For you that means: nutrient supply may support metabolism. But it cannot replace what arises from leaving things out. There is no indulgence trade here.

Medici V, Virata MC, Peerson JM et al. Alcohol Clin Exp Res. 2011;35(11):1960-1965. DOI: 10.1111/j.1530-0277.2011.01547.x

Lever 3: Change the context, not just the willpower

Two small adjustments that in practice often achieve more than grand resolutions.

First: on an empty stomach the blood alcohol curve rises more steeply. A meal with protein and fibre beforehand makes the curve flatter. That does not change the total amount that has to be broken down, but it does change the peak concentration.

Second: the last drink shifts sleep the most. If you drink, then rather earlier in the evening than late. The data on sleep architecture suggest that the second half of the night pays the price.

4.1%of all new cancer cases worldwide in 2020 were attributed to alcohol
40 gper day: from here on most people develop a fatty liver
25.9%lower HOMA index after a month off alcohol in an observational study
What this is really about

This is not a discussion about pleasure. It is a discussion about capacity.

Your liver does roughly five hundred things at the same time. Breaking down hormones, building proteins, regulating sugar, converting medication, processing immune signals. Alcohol breakdown pushes itself to the front of that list.

Energy and clarity in the morning are not a luxury. They are the visible side of free capacity. And capacity is what you get back when you give your liver fewer extra shifts.

And now you know why, with alcohol, it is not only about liver values, but about the whole nutrient and coenzyme budget behind them.

Frequently asked questions

How long does the liver need to break down one drink?
Roughly one hour per standard drink, meaning per 10 to 13 grams of pure alcohol. The decisive point is the kinetics: the enzyme alcohol dehydrogenase is already largely saturated at low concentrations. Breakdown therefore continues at an almost constant pace, no matter how much is still in the glass. Drinking more does not mean breaking it down faster, it means waiting longer. Individual speed varies considerably depending on sex, liver mass, genetics and habituation. Coffee, cold showers or exercise do not change anything relevant here according to current knowledge.
Why is acetaldehyde such a problem?
Acetaldehyde is the first breakdown product of ethanol and chemically very reactive. Review articles describe that it can bind to DNA and proteins, inhibit oxidative defence and the repair system of the cell nucleus, and disturb DNA methylation. That is exactly why it sits at the centre of the explanation for why alcohol is classified as carcinogenic. Normally acetaldehyde is converted further to acetate in the mitochondria very quickly. It becomes a problem when this second step runs more slowly than the first, for example with a genetic variant of the enzyme ALDH2.
Why does alcohol lead to a fatty liver?
Both breakdown steps, from ethanol to acetaldehyde and from acetaldehyde to acetate, consume the coenzyme NAD and leave NADH behind. The ratio of NADH to NAD shifts strongly. Fat burning in the mitochondria, however, needs free NAD. It is slowed down, while at the same time more building blocks for new fats accumulate. Fat is deposited in the liver cells. A review article in Nature Reviews Disease Primers describes that most people who drink more than 40 grams of alcohol per day develop an alcoholic fatty liver. Only a portion of them progress to more severe stages.
Does alcohol really use up glutathione?
With regular consumption, a second breakdown pathway via the enzyme CYP2E1 is upregulated. This pathway generates reactive oxygen species. Glutathione is the body's most important counterweight to that and is consumed along with this work. In cell and animal models it was also seen that the glutathione pool inside the mitochondria in particular declines under alcohol, because transport into them is disturbed. Liver cells then react more sensitively to inflammatory signals. For humans this mechanism is well reasoned, but not documented with the same certainty as through large clinical trials.
Which vitamins does alcohol cost the most?
The best described are vitamin B1, vitamin B6 and folate. With vitamin B1, lower intake, poorer absorption in the gut, disturbed conversion into the active form and reduced storage in the liver come together. With vitamin B6, older laboratory work showed that acetaldehyde can displace the active form pyridoxal 5-phosphate from its binding proteins and thereby accelerate its breakdown. For folate, one review describes four routes at once: less intake, poorer absorption, reduced uptake and storage in the liver, and increased excretion via the urine. Zinc also comes out of balance in advanced alcohol-related liver disease.
Is a hangover simply acetaldehyde?
That is the common explanation, and according to current data it is too simple. A review in Journal of Clinical Medicine summarises that blood ethanol concentration is related to hangover severity, whereas the acetaldehyde level is not to a statistically meaningful degree. Faster ethanol breakdown went along with milder hangovers. Another review names the breakdown products, changes in neurotransmitters, inflammatory signals and mitochondrial dysfunction as the most likely factors. A hangover therefore looks more like an interplay of metabolic, inflammatory and sleep costs than a single toxin.
What does a flush reaction after alcohol mean?
People who turn red in the face after little alcohol and get palpitations and nausea often carry a variant of the enzyme ALDH2 that breaks down acetaldehyde more slowly. The intermediate product backs up. A paper in PLoS Medicine describes that people with this variant who nevertheless drink regularly carry a markedly increased risk of oesophageal cancer. The variant is common in East Asian populations, but occurs elsewhere too. A pronounced flush reaction is therefore not a cosmetic detail, but a signal you can take seriously.
Can I keep drinking if I take supplements?
No, and this expectation is one of the most common misunderstandings. In a double-blind, placebo-controlled trial over 24 weeks, S-adenosylmethionine, a substance that helps regulate glutathione formation, was no better than placebo in alcohol-related liver disease. Liver values improved in both groups, and the authors attribute that to abstinence. Good nutrient supply may support metabolism. It does not replace the relief that comes from less alcohol.
Is there a harmless amount of alcohol?
For cancer risk, current data do not allow a threshold below which the risk demonstrably disappears. The WHO put it that way in Lancet Public Health in 2023. A population-based analysis for the year 2020 estimated around 741,300 new cancer cases worldwide as attributable to alcohol, about 4.1 percent of all new cases. Moderate consumption below 20 grams per day accounted for roughly 103,100 of them. That does not mean every glass makes you ill. It means the dose-response curve already rises in the lower range and that there is no protected zone.
What does an alcohol-free month achieve?
In a prospective observational study from London, 94 people with elevated consumption abstained from alcohol for one month while 47 others kept drinking. In the abstinence group the HOMA index as a measure of insulin resistance fell by 25.9 percent, systolic blood pressure by 6.6 percent, body weight by 1.5 percent, and two cancer-associated growth factors by 41.8 and 73.9 percent. In the control group nothing meaningful changed. This is an observational study without randomisation. It does show, though, how quickly measurable values can respond.
Is beer better for the liver than spirits?
For liver metabolism what counts above all is the amount of pure ethanol, not the type of drink. A small beer, a glass of wine and a shot of spirits contain roughly comparable amounts of pure alcohol. There are differences in absorption speed, in accompanying substances and in sugar content. Spirits on an empty stomach drive the blood alcohol curve up more steeply. The decisive factor, however, remains the total amount across the week and the number of alcohol-free days in between.
Can a fatty liver regress?
With pure alcoholic fatty liver, without inflammation and without scarring, regression under abstinence is considered well possible. Review articles describe that several clinical studies have shown regression of steatohepatitis and fibrosis under abstinence, and that survival can improve even in advanced stages. How far something regresses depends on the stage, on the duration and on accompanying factors such as excess weight, diabetes, smoking and viral hepatitis. Assessment in an individual case belongs in a medical examination with laboratory tests and imaging.
SJ

Shukri Jarmoukli

Physician, Integrative Medicine · ViveCura Berlin

I work in Berlin at the intersection of general medicine, clinical psychoneuroimmunology and functional diagnostics. The focal points of my practice are detoxification and heavy metal diagnostics, gut restoration, mould exposure and ketamine-assisted treatment.

On every topic, what interests me is the question of what actually happens at the cellular level. Not because mechanisms are the whole answer, but because they explain why measures work in one person and not in the next.

Privatpraxis ViveCura · Skalitzer Straße 137, Berlin

Related topics from other areas

Alcohol touches several systems at once. These articles from other clusters follow up the adjacent questions.

Sources

All statements were checked against abstracts and citation data. The markers in square brackets indicate the level of evidence. Mechanistic statements on mitochondrial glutathione and on peroxisomal beta-oxidation rest largely on cell and animal models. They are biologically plausible, but not documented in humans with the same certainty as through large randomised trials.

  1. Seitz HK, Bataller R, Cortez-Pinto H et al. Alcoholic liver disease. Nat Rev Dis Primers. 2018;4(1):16. DOI: 10.1038/s41572-018-0014-7 [Review article]
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  6. Cioarca-Nedelcu R, Atanasiu V, Stoian I. Alcoholic liver disease, from steatosis to cirrhosis, a biochemistry approach. J Med Life. 2021;14(5):594-599. DOI: 10.25122/jml-2021-0081 [Review article]
  7. Yu HS, Oyama T, Isse T et al. Formation of acetaldehyde-derived DNA adducts due to alcohol exposure. Chem Biol Interact. 2010;188(3):367-375. DOI: 10.1016/j.cbi.2010.08.005 [Mechanism review]
  8. Brooks PJ, Enoch MA, Goldman D, Li TK, Yokoyama A. The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption. PLoS Med. 2009;6(3):e50. DOI: 10.1371/journal.pmed.1000050 [Review article]
  9. Pár A, Pár G. Alcoholic liver disease: the roles of genetic-epigenetic factors and the effect of abstinence. Orv Hetil. 2019;160(14):524-532 (Hungarian). DOI: 10.1556/650.2019.31352 [Review article]
  10. Garcia-Ruiz C, Fernandez-Checa JC. Mitochondrial glutathione: hepatocellular survival-death switch. J Gastroenterol Hepatol. 2006;21 Suppl 3:S3-S6. DOI: 10.1111/j.1440-1746.2006.04570.x [Mechanism review]
  11. Fernández-Checa JC. Alcohol-induced liver disease: when fat and oxidative stress meet. Ann Hepatol. 2003;2(2):69-75. PubMed ID 15041894 (no DOI assigned) [Mechanism review]
  12. Zhang Y, Zhang W, Li Y et al. Induction of peroxisomal beta-oxidation as a critical mechanism for ethanol-induced hepatic triglyceride accumulation. FASEB Bioadv. 2025;7(6):e70013. DOI: 10.1096/fba.2024-00211 [In vivo, mouse]
  13. Medici V, Halsted CH. Folate, alcohol, and liver disease. Mol Nutr Food Res. 2013;57(4):596-606. DOI: 10.1002/mnfr.201200077 [Review article]
  14. Lumeng L. The role of acetaldehyde in mediating the deleterious effect of ethanol on pyridoxal 5-phosphate metabolism. J Clin Invest. 1978;62(2):286-293. DOI: 10.1172/JCI109128 [In vitro, rat hepatocytes and human erythrocytes]
  15. Chandrakumar A, Bhardwaj A, 't Jong GW. Review of thiamine deficiency disorders: Wernicke encephalopathy and Korsakoff psychosis. J Basic Clin Physiol Pharmacol. 2018;30(2):153-162. DOI: 10.1515/jbcpp-2018-0075 [Review article]
  16. Cantu-Weinstein A, Branning R, Alamir M et al. Diagnosis and treatment of Wernicke's encephalopathy: a systematic literature review. Gen Hosp Psychiatry. 2024;87:48-59. DOI: 10.1016/j.genhosppsych.2024.01.005 [Systematic review]
  17. McClain C, Vatsalya V, Cave M. Role of zinc in the development and progression of alcoholic liver disease. Curr Treat Options Gastroenterol. 2017;15(2):285-295. DOI: 10.1007/s11938-017-0132-4 [Review article]
  18. Mackus M, van de Loo AJ, Garssen J, Kraneveld AD, Scholey A, Verster JC. The role of alcohol metabolism in the pathology of alcohol hangover. J Clin Med. 2020;9(11):3421. DOI: 10.3390/jcm9113421 [Review article]
  19. Palmer E, Tyacke R, Sastre M, Lingford-Hughes A, Nutt D, Ward RJ. Alcohol hangover: underlying biochemical, inflammatory and neurochemical mechanisms. Alcohol Alcohol. 2019;54(3):196-203. DOI: 10.1093/alcalc/agz016 [Review article]
  20. Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB. Alcohol and sleep I: effects on normal sleep. Alcohol Clin Exp Res. 2013;37(4):539-549. DOI: 10.1111/acer.12006 [Review article]
  21. Mehta G, Macdonald S, Cronberg A et al. Short-term abstinence from alcohol and changes in cardiovascular risk factors, liver function tests and cancer-related growth factors: a prospective observational study. BMJ Open. 2018;8(5):e020673. DOI: 10.1136/bmjopen-2017-020673 [Real-world, prospective, n=141]
  22. Medici V, Virata MC, Peerson JM et al. S-adenosyl-L-methionine treatment for alcoholic liver disease: a double-blinded, randomized, placebo-controlled trial. Alcohol Clin Exp Res. 2011;35(11):1960-1965. DOI: 10.1111/j.1530-0277.2011.01547.x [RCT, double-blind, n=37]
  23. Rumack BH. Acetaminophen misconceptions. Hepatology. 2004;40(1):10-15. DOI: 10.1002/hep.20300 [Review article]

This article is for information and does not replace medical advice, diagnosis or treatment. In pregnancy, with existing liver disease, with regular medication use or where alcohol dependence is suspected, the assessment belongs in medical hands.

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