On Alcohol Dehydrogenase

A Doctor's Musings On Why We Have an Enzyme Designed to Process Alcohol

Last Updated: December 17, 2016


From time to time, varoius people ask me a variation of the following question:

“If God didn’t intend for us, humans, to drink alcohol, why do we have an enzyme, alcohol dehydrogenase, in our liver and other tissues and cells, whose function is to process (metabolize) alcohol?”

On Alcohol Dehydrogenase and God

Few things have been as prevalent across cultures and ages as alcohol consumption.

First, I have to preface this by saying I wrote this article with sincere believers in mind, who sometimes ask themselves questions like this, and who are looking for reasonable answers.

The other reason I wrote this was as a response to some who are arguing that drinking alcohol is a perfectly acceptable behavior for Christians. If God didn’t intend for us to use alcohol, they contend, he wouldn't have placed the enzyme to process it in a lot of the cells in our bodies, would he?

I’ve learned that questioning the reasons God did or didn’t do something a certain way leads, invariably, to us ultimately realizing how ignorant we are. This issue is no exception.

I will first try to explain what alcohol dehydrogenase is, then discuss the issue of endogenous (i.e. internally generated alcohol), and I will end with some practical suggestions.

What is Alcohol Dehydrogenase (ADH)?

ADHs are actually a group of enzymes present in most living organisms that facilitate the chemical conversion of alcohols to ketones and aldehydes (and vice versa). In the process, they cause the reduction (or oxydation) of another compound, NAD+, to NADH. NAD is a coenzyme, whose main function is to carry electrons from one chemical reaction to another.

Notice the word alcohols above. That is the first clue to the answer as to why we have these enzymes in our bodies: their substrate is not just ethanol (the mind altering substance in alcoholic beverages), but several other alcohols that have nothing to do with making people drunk. Here are a couple of important examples:

  • AHD oxidizes methanol, a very toxic/poisonous type of alcohol, rendering it harmless (except when large amounts are ingested) by converting it (ultimately) to oxalic acid.
  • ADH acts on vitamin A (which, chemically speaking, is an alcohol, also called retinol), converting it into retinoic acid, a hormone with major functions in growth and development.

It is important to understand that ADH enzymes are present in most animals, as well as in plants, bacteria and yeast. In fact, ADH was first discovered in a yeast, Saccharomyces cerevisiae (brewer's yeast). In yeast and bacteria, though, ADH enzymes generate alcohol by converting glucose (sugar derivatives) into ethanol, which is the opposite reaction to that occurring in humans.

This last point takes us to the next chapter, which has to do with endogenous alcohol.

What is Endogenous Ethanol?

As a practicing primary care physician, I often order drug screens for patients that use controlled medications, such as narcotic pain killers. The purpose of these screens is twofold. First, we want to make sure that the medications we prescribe are taken (and not given to somebody else, or sold on the black market). Second, we want to ensure people are not using other illicit drugs or alcohol at the same time they are taking these powerful medications, and thus risking serious side effects or even death.

In the process of reviewing the results of these drug screens, I sometimes come across some that show a small amount of alcohol in patients who are adamant they never touch alcohol. I have been around long enough to be able to trust some of these patients, so I am confident the phenomenon is real. Plus, the medical literature documents such occurrences. More extreme, albeit very rare, cases of this even have been given an exotic name: auto-brewery syndrome.

Small amounts of alcohol (ethanol) are generated in our digestive tract by bacteria and yeast and are absorbed into the bloodstream, together with the other nutrients. This is what endogenous alcohol is. Fortunately, we don’t walk around half-drunk after each meal for at least two reasons:

  • The amount of ethanol produced in this manner is very small.
  • The body was designed such that all the blood vessels that serve the digestive tract, absorbing nutrients, alcohol, toxins and whatever else we ingest or produce in our guts, is filtered by the liver. And since the liver has the largest amount of ADH in the body, it has no problem metabolizing the endogenously generated ethanol. Ethanol levels leaving the liver are about 15 times lower than those in blood coming to liver from the intestine.
As I hinted above, there are some extreme cases of this phenomenon. I will mention here a few:

Before I leave the endogenous alcohol alone, I wanted to touch on another issue: there is a distinct possibility that ethanol is produced in various cells in our bodies as an intermediary or side product of metabolism. My biochemistry memories are rusty, and I didn’t have enough time to dig up before writing this article to determine if this issue is settled in the specialty literature, but I will update it when possible. If, indeed, ethanol is produced inside our bodies in this manner, that would be another reason why most tissues need ADH.

A Mitigating Strategy?

As Christians, we worship an Omniscient God. From this perspective, it is not difficult to think that God, in his prescience, was able to foresee the fact that fallen human beings would develop a taste for ethanol, or be accidentally exposed to it. ADH would function, in this scenario, as a protective means against alcohol poisoning.

We know how toxic ethanol can be in cases of severe inebriation, when the liver’s ability to detoxify it is overwhelmed. Intoxication can be deadly. We also know, for example, that young women, who have lower levels of liver ADH, have a significantly lower tolerance to ethanol ingestion. So do people with liver disease.

As I said before, we tend to build a “straw God” in our minds, and then we tell him what he can and cannot do. In this particular example, some people reason that if God endowed them with ADH, he meant for them to drink. What I’m trying to say is quite the contrary: the fact that God gave us ADH can be seen as an act of mercy, to save us from the toxic effects of alcohol, even though he told us to avoid it in the first place.

It would not be the first time God acted in this manner: despite making it clear marriage was a union between one man and one woman, for life, he tolerated and worked with people who practiced polygamy and / or divorce. He was (and still is) able and willing to forgive all sorts of sins, and redeem people most of us would see fit to spend their remaining days in prison. In fact, the main reason a lot of people find some stories from the Bible repulsive is exactly this: we focus on the outrageous things the human characters in those stories have done, forgetting the main point these stories make is we have a God willing to go the extra mile to redeem the lost.

This damage mitigating purpose of ADH is somewhat speculative, though, and I will leave it at that.

Some Concluding Thoughts

To summarize, there are at least three reasons why we have ADH enzymes in our bodies:

  1. To process other alcohols than ethanol.
  2. To process endogenous alcohol generated by the gut bacteria and yeast, and possibly our own bodies.
  3. As a mitigating measure to protect against accidental or intentional alcohol intoxication.

This issue illustrates very well several points:

  1. Reality is much more complex than what we expect. All too often, when we learn of something new, we tend to rush and make all kinds of assumptions about it. It helps to be patient and try to understand the whole picture.
  2. We should be mindful of the logic we use in making the case for something. Using the logic of the initial question, one may conclude we should partake of all the pharmacological products present in prescription drugs, since we have enzymes and metabolic pathways to process and neutralize them. Not a smart idea!
  3. We should be extra careful when we ascribe motives to what God did.

Dr. Gily Ionescu MD, MS.

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