“The Cause of Ulcers is Bacteria” Makes as Much Sense as “The Cause of Car Accidents is Cars”

If I were to look at you, and say, in a serious tone of voice, “The cause of car accidents is cars”, you’d think I’m nuts. It’s not a useful statement. Yet many medical and science experts — including the people who award the Nobel Prize in Physiology or Medicine — believe it is helpful to say “the cause of ulcers is bacteria”. The two statements are similar because only a small percentage of cars get in accidents and only a small percentage of people infected with H. pylori, the bacterium that supposedly “causes ulcers”, get ulcers. A helpful investigation of what causes ulcers would figure out the crucial difference(s) between those infected with H. pylori who don’t get ulcers (almost all) and those who do (very few).

I recently encountered the “the cause of ulcers is bacteria” twice in one day. Once in a book review by John Timpane:

Barry Marshall, who discovered what causes stomach ulcers, played fast, loose, and messy with his methods and data. He was right, and got the right answer, and now we know.

(Timpane is right about the “fast, loose, and messy” part. Marshall ingested a large number of H. pylori. He failed get an ulcer — and claimed the outcome supported his view that H. pylori causes ulcers.) And once in The New Yorker, in a long article about the benefits of microbes, especially H. pylori, by Michael Specter:

In 1982, to the astonishment of the medical world, two scientists, Barry Marshall and J. Robin Warren, discovered that H. pylori is the principal cause of gastritis and peptic ulcers.

Should I expect science journalists to understand causality? Maybe not. But it is interesting that the people who award the Nobel Prize in Medicine and “the medical world” do not understand it.

10 Responses to ““The Cause of Ulcers is Bacteria” Makes as Much Sense as “The Cause of Car Accidents is Cars””

  1. Mark Says:

    I agree, and think that another good analogy would be saying that having no Y chromosome is a cause of pregnancy.

  2. Nancy Lebovitz Says:

    “Ulcers are caused by bacteria” is still an improvement over “ulcers are caused by stress and/or spicy food”.

    Seth: That’s not clear. Maybe 99% of everyone is infected with H. pylori and, of those infected, only those exposed to stress develop ulcers. If so, the old thinking (“ulcers are caused by stress”) was better than the new thinking (“ulcers are caused by bacteria”).

  3. RAD Says:

    Seth, I’m grasping to understand your logic. As I understand it, the causality is H. pylori Infection -> Chronic Gastritis -> Gastric Ulcers -> Gastric Cancer. Prior to Barry Marshall the presumed causation was Stress -> Gastric Ulcers. Marshall did not get ulcers after his experiment but he immediately had symptoms of chronic gastritis.

    Are you saying there is no causation between H. pylori and chronic gastritis or are you saying that you would like to see more qualifiers when people discuss the association between the PRESENCE of H. pylori and chronic gastritis (which I think is low)?

    Seth: I don’t know if ordinary amounts of H. pylori cause gastritis (Marshall ingested an unusually large amount), nor do I know what fraction of gastritis cases are associated with H. pylori. So I can’t answer your question.

  4. Alex Chernavsky Says:

    Seth, is there an article or a paper that — in your view — accurately describes the etiology of ulcers? I’m asking because I’m not clear about your specific objections to the H. pylori hypothesis.

    Seth: I don’t know of one. As far as I can tell, the etiology is almost completely unknown. Most people have H. pylori infection. Almost no one gets ulcers. Why do some people with H. pylori infection get ulcers? Very little is known about this. My objection to the H. pylori hypothesis is that it has confused a lot of people. A lot of people think it is well-understood what causes ulcers. That’s not true.

  5. Nancy Lebovitz Says:

    I think Seth’s point is that there hasn’t been further investigation into what some people are get serious h. pylori infections and others don’t.

  6. K Daniel Says:

    If, as you proclaim, ulcers are NOT caused by bacteria then why does the now standard treatment for ulcers (a two-combination course of antibiotics) “cure” ulcers in the vast majority of cases? What, in your opinion, is causing the ulcers that are “cured” by the antiobiotics?

    If you can’t answer that question then I have a new theme: Seth’s blog is related to science the same way that creationism is related to evolution.

    Seth: Ulcers supposedly cured by antibiotics come back very frequently. In your haste to say something derogatory, you seem to not have fully understood my comment. I don’t claim to know what distinguishes people infected with H. pylori who don’t get ulcers (almost everyone) and those infected with H. pylori who do get ulcers (a tiny fraction).

  7. dearieme Says:

    “what distinguishes people infected with H. pylori who don’t get ulcers (almost everyone) and those infected with H. pylori who do get ulcers (a tiny fraction)”: that’s a very good point, and one that I hadn’t appreciated. Why on earth hasn’t it been investigated properly?

  8. GB Says:

    Hi Seth,
    Apologies for the change of topic, but I don’t know how else to contact you. I’m keen to buy Shangri La diet on my kindle, and I know there’s a version available for sale. But as soon as I log into my Amazon account, I’m no longer offered the opportunity to buy it. It’s like the kindle version no longer exists, only the physical hard cover and paperback versions are available to me. I’m in Australia, and suspect the book is not offered there for some sort of licencing reason.
    Are you aware of this? Many people Down Under could use your book these days.
    Thanks for your scientific contribution and great blog.

  9. Mark Says:

    Do antibiotics actually “cure” the ulcer, or do they just help to meliorate the symptoms? These are two vastly different things. Perhaps H. pylori simply exacerbate the symptoms (e.g., by causing irritation or inflamation), so antibiotics appear to “help” the ulcer (but in fact they’re doing no such thing). The bottom line, as Seth pointed out, is that if H. pylori is the “cause” of ulcers, then how can the majority of the world’s population be infected but very few actually have ulcers?

    This is all very similar to the whole “high cholesterol causes heart disease” myth.

  10. JM Says:

    Based on a number of things I have read about H. pylori and ulcers, my personal thoughts are that if almost all of us carry the bacteria then those who do get ulcers it is because the bug has found a weakness in their natural defenses and used it to attack the stomach lining – whether that weakness is caused by stress, diet or something else hasn’t been determined.

    Also found this article very interesting – a small study found a link between the presence of H. pylori and atrial fibrillation of the heart. At the end of the article there is the statement “H. pylori is a very resilient bacterium and has properties that enable it to escape detection by the immune system”

    http://www.sciencedaily.com/releases/2005/06/050616062204.htm