Does breastfeeding cause autism?

breastfed brain

Over the past 4 decades, there has been a shocking rise in the prevalence of autism. Antivax activists point out that there has been an dramatic increase in the number of vaccines that infants receive and conclude that vaccines cause autism. But here has also been a dramatic increases in breastfeeding rates. It is time for us to ask: Does breastfeeding cause autism?

The above image relates the statistics and the graph below illustrates the trend.

autism prevalence vs breastfeeding initiation

It’s pretty dramatic, isn’t it? So we should be rushing to investigate whether breastfeeding causes autism, right? We should direct our attention to the CDC recommendations designed to encourage breastfeeding and ask if the CDC is ignoring the harmful effects of breastfeeding, right? We should view lactation consultants with suspicion and we should demand that they inform new mothers of the very clear association between breastfeeding and autism, right?

Wrong!

Why not? Because correlation is not causation. Just because two phenomena rise is parallel does NOT mean that one caused the other.

If correlation is not causation, what is?

To determine if Event A caused Disease B, we need to investigate whether it satisfies Hill’s Criteria. These are 9 criteria, most of which much be satisfied before we can conclude that Event A is not merely correlated with Disease B, but Event A actually causes Disease B.

Who was Hill and why should we care about his criteria?

…These criteria were originally presented by Austin Bradford Hill (1897-1991), a British medical statistician as a way of determining the causal link between a specific factor (e.g., cigarette smoking) and a disease (such as emphysema or lung cancer)… [T]he principles set forth by Hill form the basis of evaluation used in all modern scientific research… Hill’s Criteria simply provides an additional valuable measure by which to evaluate the many theories and explanations proposed within the social sciences.

What are the criteria?

1. Temporal relationship: It may sound obvious, but if Event A causes Disease B, Event A must occur before Disease B. The is the only absolutely essential criterion, but it is NOT sufficient. Lay people often erroneously assume that because it’s the only essential criterion, it is the only criterion that counts. For example, vaccine rejectionists often point to the fact that childhood vaccinations usually occur before the onset of autism, but that does not mean that vaccination causes autism. Similarly, breastfeeding occurs before the onset of autism. Consider that learning to walk usually precedes autism, but obviously learning to walk does not cause autism.

2. Strength: This is measured by statistical tests, but can be thought of as similar to the closeness of the relationship. Is Disease B always preceded by Event A? Sometimes? Only rarely? Does Event A always cause Disease B? Sometimes? Only rarely? Lung cancer is not always preceded by cigarette smoking, but it usually is. Cigarette smoking does not always lead to lung cancer, but it does often lead to lung cancer. In other words, the relationship is fairly strong.

In the case of breastfeeding (or vaccines) and autism, breastfeeding (or vaccines) usually precede the diagnosis. However, most children who receive vaccines don’t develop autism. Thus the relationship is weaker.

3. Dose-response relationship: If cigarette smoking causes lung cancer, we would expect that smoking more cigarettes would increase the risk of lung cancer, which it does. In contrast, there appears to be no dose-response relationship between the length of breastfeeding (or the number of vaccinations) and the risk of developing autism.

4. Consistency: Have the findings that purported to show a relationship been replicated by other scientists, in other populations and at other times? If studies fail to consistently show the relationship, causation is very unlikely.

This is a critical point. One experiment or even a few experiments is NOT enough to determine causation. A large number of experiments that consistently show the same result is required. This is particularly important for vaccine rejectionists to note. The fact that a few studies claim to have shown that vaccination causes autism is meaningless when a very high proportion of studies show that there is not even a correlation between vaccination and autism.

5. Plausibility: In order to claim causation, you MUST offer a plausible mechanism. In the case of cigarette smoking, certain components of the smoke are known to cause damage to the cells inside the lungs, and cellular damage has been shown to lead to cancer. In contrast, no one has yet offered a plausible explanation for how breastfeeding (or vaccines) “cause” autism. In fact, no one can even agree on the specific component that is supposedly responsible.

6. Consideration of alternative explanations: This is self explanatory. In the case of breastfeeding (or vaccines) and autism, there is a very simple alternative explanation. Autism cannot be diagnosed before the age of 2 and breastfeeding (and most vaccines) are given before the age of 2.

7. Experiment: If you alter Event A do you still get Disease B. In the case of smoking, if you quite smoking, the risk of lung cancer goes down. In the case of breastfeeding (or vaccines) and autism, if you forgo vaccination, the risk of autism remains unchanged.

8. Specificity: Is Event A the only thing that leads to Disease B? This is the least important of the criteria. If it is present, it is a very powerful indicator of causation. For example, among young women who developed a rare form of vaginal cancer, all of them were found to have been exposed to DES (diethylstilbestrol) while in utero. That is a highly specific effect.

However, even if the relationship is not highly specific, that does not preclude causation. Though there are non-smokers who get lung cancer, it does not change the fact that the other criteria show that smoking causes lung cancer.

9. Coherence: The explanation of action must comport with the known laws of science. If the purported mechanism of causation violates the law of gravity, for example, then it isn’t acceptable. That’s why religious arguments against evolution are wrong. They are “incoherent” since they invoke forces outside science.

What do Hill’s criteria look like in action?

In the case of cigarette smoking and lung cancer, 8 out of 9 Hill’s Criteria are satisfied. In contrast, in the case of breastfeeding (or vaccines) and autism, only 3, possibly 4 criteria are satisfied. This is why we can say that the scientific evidence shows that breastfeeding (or vaccines) do not cause autism.

While it is true that breastfeeding (or vaccines) usually precede the diagnosis of autism, that is an essential criterion, but not enough. The fact that is there is no dose-response relationship, that the few studies that showed a purported relationship cannot be replicated and that there are no studies in which people who were not breastfed had a lower incidence of autism.

That’s how we know that breastfeeding does not cause autism.

That’s also how we know that vaccines don’t cause autism, either!

 

Adapted from a piece that first appeared in February 2011.

  • Sue

    I love this site – an index of spurious correlations:

    http://www.tylervigen.com/

  • The Bofa on the Sofa
  • Dr. W

    The simplicity of this argument and the accuracy with which it hits the woo exactly where it lives is as beautiful as it is brutal. Like a ballet with “OMG, use of a foreign object! Oh the humanity!”

  • Felicitasz

    YES!!!!!!!!!!!!

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  • The Computer Ate My Nym

    I’m sorry, I can’t help myself: http://xkcd.com/552/

  • Guesteleh

    Sadly, you’re going to get women who won’t read past the first paragraph roaring in here screaming ZOMG, “Dr” Amy is lying about breastfeeding!!!!

  • Cobalt

    http://breastpump.media.mit.edu/

    Moms who pump, or have pumped, or might one day pump, or if you know someone who might fit one of those categories well enough to discuss it with them, might want to check this out. Ignore the one paragraph about why breastmilk is important, because they missed the point there, but the results are still pretty cool.

    • Hannah

      I am extremely distracted by the fact that the far-left woman in the first photo looks freakishly like my cousin (as in, had to go look close for another minute to be sure it wasn’t her).

      That said, some of these things sound kinda cool and useful if they ever are able to get out there.

  • fiftyfifty1

    Fact: Austin Bradford Hill was born in 1897, at a time when Austin was a very rare first name. Fact: Austin Hill later created a famous set of criteria.Fact: Austin is now a popular first name. Coincidence? I think not!

    • Roadstergal

      Fact – Austin is a city in Texas. Fact – I once said Autism to a Texan, and they heard Austin. Just coincidence?

      • The Bofa on the Sofa

        Another true fact: Steve Austin is the 6 million dollar man and he was from the United States. There are currently 6 million people in the US with autism. Coincidence?

        And Jamie Sommers was the bionic woman, and Max was the bionic dog. He was a German Shephard. Steve Austin had a bionic eye and Jamie Sommers had a bionic ear, although it’s not quite clear how someone needs a bionic ear after a skydiving accident. I don’t know what Max’s bionic parts were, although both the 6 million dollar man and the bionic woman both had bionic legs and arms.

        • Amy M

          Probably the air pressure changes that took place while plummeting from the sky ruptured her ear drum and permanently damaged her hearing. (hence the bionic ear?)

  • GiddyUpGo123

    Thank you for this, from a lay person’s perspective. I often tell people, “correlation does not equal causation” but I also didn’t know anything about the Hill criteria, and you explained it very clearly.

    • sdsures

      They never mentioned the Hill criteria in the courses I took in research methods in psychology, either. We were just told that we had to learn this basic thing and accept it – not the why behind it.

  • Dorit Reiss

    Thank you for this clear discussion of the Hill criteria and their application in this context. Really helpful.

  • rational adult

    First time commenter. This seems like a fine time to share my recent experience. Background: My 2 year old has autism. I am currently pregnant. I will be primarily treated by and deliver with an OB but at my Boston-area practice the model is that everyone sees a CNM for their initial prenatal appointment. At the prenatal appointment, the CNM asked me if “there is anything I want to do differently this pregnancy in light of my first child’s autism?” In the brief pause while I was scraping my jaw off the floor she continued by saying that “for example, if you choose not to get your flu shot that would be understandable.”

    I’ve thought a lot about what I could or should have said in that moment but at 8 weeks pregnant, queasy, and anxious to get through the discussion and hear the fetal heartbeat, I did not put up much of a fuss. I told her that I already got my flu shot and I told her that I am aware that vaccines do not cause autism. She replied that she knows that too, but “we are an individualized practice here.”

    This was at one of the largest physician systems in New England and I will be delivering at one of the nation’s top hospitals. People, the woo is everywhere. I would love to hear from some of the contributors here who practice medicine (maternal or otherwise) how you would handle a pregnant patient who did not want to get a flu shot. And… What should I have said? And should I file a formal complaint or is it not worth it.

    • Ash

      I think it’s worth sending a quick message to Patient RElations. Doesn’t take very long.

      • rational adult

        Ash, if I had time to type it here I should have time to send it to Patient Relations. You are right. I can use a lot of what I wrote in this comment. I am going to also spell out the reasons that I was appalled and angry. I figure it should be self evident for readers here. 🙂

        • lizdexia

          Patient Relations Specialist here! Pretty please file a complaint, even better if it is written. Either this is one screwball provider who is pushing a terrible agenda, or someone in this practice is making a choice to try and accomodate the views they think their patients hold. If it’s the former, the medical director needs to know asap. If it’s the latter, one of the most effective ways for someone like me to drive change in a bad practice is to be able to demonstrate that patients do not want this (in addition to it being terrible clinical care).

          • CrownedMedwife

            In agreement with the first point in that Medical Director needs to be made aware if the CNM is pushing an AntiVaccine agenda. Simple resolution.

            I also agree,in part, with the latter in that it is possible the CNM was trying to accommodate the perceived views of the patient with respect to offering to withhold a recommended vaccine based on an unfounded fear of vaccines in pregnancy. Not such a simple resolution.

            The second presumption assumes health care providers have to offer an alternative level of care in order to please the patient, rather than offering and providing a standard level of care. When it comes to vaccines, patients usually present as one of three groups; as willing to receive whichever vaccines are recommended, leaning towards vaccines but need additional information and reassurance on safety or with strong antivaccine views and deep rooted beliefs (misperceptions) about vaccines. In my practice each of the above listed patient types receive the same information regarding vaccines in pregnancy with the third group inevitably requiring an extended time for discussion. While I won’t force a vaccination, I also won’t pander to the AntiVaccine types and validate their misheld beliefs.

            The OP’s provider failed, plain and simple. Fortunately, Rational Adult was rational enough to know the difference. Unfortunately, until her CNM is held accountable, there will inevitably be mothers in the second and third group who won’t know they were failed. Worse yet, women in the the third group will leave unprotected AND validated in their beliefs by a CNM only to perpetuate the mistruths associated with vaccines.

          • Margo. Nz

            Sometimes hard to find the right balance, when offering advice…we in NZ do recommend the flu vaccine, however, we also are required to acknowledge that this is a personal choice issue and so have to work hard at giving well researched facts to women….we have to leave the choice to have vac or not with them….

          • Young CC Prof

            Patients always have a choice. However, healthcare providers have the responsibility NOT to imply that vaccinating or not are both equally valid and reasonable choices for most people, just like the choice of whether to add marshmallows to your hot chocolate.

          • Margo nz

            Respectfully, I will have to disagree with you re responsibility NOT to imply…. We give the Facts…..discussion follows, choices are made ,not my place to imply one choice more valid than other choice….that, in my opinion would be disrespectful…..and also might be seen by the woman as me, the health professional ,leading,coercing, pressuring…even though at times I have felt like doing just that ….

          • alannah

            Protecting yourself and your unborn child against a potentially deadly disease is a more valid choice than declining the shot because of misguided antivax beliefs

          • Dr Kitty

            Margo, how on earth do you present the fact that 11% of maternal mortality in the UK between 2008-2012 was due to ‘flu, that ‘flu vaccination is safe and effective and recommended in pregnancy by all major health organisations WITHOUT presenting it as a more valid choice?

            If someone is wavering, I’ll ask, specifically, what their concerns are. Often they worry about teratogenicity. I’ll explain that there is no evidence that vaccination causes damage to the foetus, but if they wish to delay vaccination until the early second trimester when the baby is more fully formed I’ll support that.

            It is disrespectful to tell your patients you think they are making good choices when they aren’t. Think about other areas of medicine. Would you support the renal patient who eats 10 bananas a day, or the cardiac patient who puts salt on everything? No, you’d tell them their choices were unhealthy and that there was good evidence they were causing harm.

            You can support their right to make that choice while explaining that you don’t think it is a smart one.

          • Dr Kitty

            Oh, Margo, out of interest, what is your practice’s vaccination rate for flu vac in pregnancy?

            Mine is over 98%.

          • Margo nz

            We had a nationwide campaign for Flu vac and whooping cough last year in NZ, through NZ ministry of health. Midwives advise and refer women to their general practioners for the flu vac and whooping cough vac….whooping cough was a major concern last year as was the flu. I would say that of the women seen by me in pregnancy around 90 per cent made the decision to have the vac…..I am not saying I tell women they are making a good choice when opting out of vac….I am saying that sometimes, even after lengthy discussion, women make a decision not to vac and I have to accept that….I might not agree with their decision, but it’s all about choice and informed consent…..when I worked as an orthopaedic nurse I used to get frustrated with patients who chose not to follow the best specialist advice given to them by the surgeon, but again….people make choices wisely and sometimes unwisely….in spite of good solid research based information.

          • Dr Kitty

            A lengthy discussion in which you imply that vaccinating and not vaccinating are equally valid choices. Do you tell them you think it’s the wrong choice? Do you tell them that your practice is barely maintaining levels necessary for herd immunity because of people like them?

            By all means tell them that the choice is theirs, but that it isn’t based on evidence or common sense and has potentially fatal consequences.

          • Margo nz

            No I don’t imply not vaccinating has equal validity I refer to research based evidence and re explore the reason why they would make a choice that flies in the face of good research….I leave the door open for further discussion. I give facts re herd immunity is low in our area and that relying upon other families to vac whilst not taking up the free schedule is questionable if after all that the choice is made not to vac I have to respectfully disagree with choice,whilst maintaining a good working relationship with the woman, challenging at times. The immunisation schedule post bsby is free and if parents opt out of schedule mmr etc then the name of child goes on a opt off register. Schools and day care can’t exclude un immunized kids but they have access to names of kids not on free schedule. Pretty frustrating, at times, but people make their choice, so…..

          • MLE

            Yeah this is not a Coke vs. Pepsi situation. If my provider is acting like it IS a matter of personal preference and one choice is no better than another, I will take my cues from them and act accordingly. I would be irate if I found out later that this was not the case.

          • Life Tip

            If my healthcare provider isn’t pressuring me to get the flu vax, I’m finding a new doctor. One choice is more valid than the other.

            Anti-Vaxxers take any hint of validation a run amok. If a CNM said this to many anti-vaxxers, they’d be posting “my doctor admits the flu vaccine causes autism!!!1!” all over Facebook and babycenter the minute they stepped out of that office.

          • Mariana Baca

            Sorry, no. The reason I go to doctors is not simply as medicine dispensers, but I want to know which medical choices are better than others. That is the whole point. If they are telling me it is equally valid to use homeopathy drops or a decongestant, they are not doing their job, for example. I can ignore their advice, but if they don’t offer or imply which is better, there is no point to going to them.

    • Roadstergal

      “for example, if you choose not to get your flu shot that would be understandable”

      OH MY FUCKING GOD.

      I mean, it’s not like the flu is particularly problematic for pregnant women, or anything.

      • SporkParade

        I was watching survivors testimonies about the Spanish Flu the other day. One of the more remarkable observations was from a woman who was a child in the backwoods, with no access to doctors and no treatment available except aspirin. She said, “No one who was pregnant survived the flu.”

    • alannah

      Yes! Definitely file a formal complaint.
      Influenza is a major cause of serious morbidity and mortality among pregnant women. Encouraging pregnant patients to skip their flu shot is utterly irresponsible and against all guidelines and standards of care. I am sure that your OB will want to reconsider this midwife’s position in his practice when he finds out that she is actively spreading antivax propaganda among his patients.
      You should write a letter factually stating dates, places and names, and quoting her words. Ask if the midwife’s views about autism and vaccines reflect those of the practice as a whole and express your concern. Tell them you want a formal apology and their plan to ensure that this won’t happen to other moms. And of course you should never have to see that midwife again (if they decide not to sack her! )

      • rational adult

        Thanks alannah. My career is in insurance claims so I am no stranger to the complaint that is obscured by emotion or invective. That is part of why I have waited to write a complaint, I needed some weeks of distance to process and be, well, rational! Rather than an apology, I would like assurance that other women are not dissuaded from getting the flu shot.

        • Guesteleh

          Copy the CEO of the hospital they’re affiliated with. I’m sure they’d love to know that some wooey nurse is sending potential flu patients to their maternity ward.

        • Ob in OZ

          I would talk to the OB, especially if you have any relationship past or present. They may ask you to put something in writing. Sometimes they just need to hear it to put a stop to to this kind of stupidity. Do what you think would help you feel comfortable returning to their practice for your next visit. If you’re planning on switching practices because of this (very reasonable), then make it clear in writing why that is the case. I have been shocked by what the flu can do to a healthy young pregnant woman…twice.

      • theadequatemother

        last flu season we had a couple of pregnant patients on ECMO (extra-corporal membrane oxygenation aka bypass).

    • Amy M

      Wow. Of course that was completely unacceptable, but now I’m curious as to what else this quack might suggest to “decrease the risk of autism.” I’m sure it would be equally offensive and ignorant.

      • rational adult

        I can only imagine. Don’t go skiing? Drink more raw camel milk?

        • Amy M

          Don’t stand in the same room as a microwave? Oh wait, I know, don’t expose yourself to ugly words, like “Hitler” or “Satan.” That’s gotta be it.

      • Mishimoo

        Avoid ultrasounds and pitocin are the ones I’ve heard.

        • DaisyGrrl

          I’ve also heard epidurals cause autism.

      • The Computer Ate My Nym

        Last time I reviewed the evidence at all, your best bet for avoiding autism in offspring was “pick different grandparents for them”. Sorry, but the only so far known correlates are genetic.

        • Amy M

          I thought there was a also an association with age of parents at conception? Or has that been thrown out? It was both parents too, not just mom—of course, once a woman is pregnant the only way to remedy that one is to find a time machine.

    • sr27

      I thought there was a study that came out in the last few years that showed if a woman got the flu during pregnancy it was more likely that the child would develop autism. That should lead to care providers recommending flu vaccines even more, shouldn’t it?

      • Mishimoo

        There was one that appeared to show an increased risk of schizophrenia if the mother caught influenza while pregnant, but I’m not sure how well it was conducted.

        • Young CC Prof

          That one might be tough to demonstrate, simply because you’re connecting events 2-4 decades apart. The link to prematurity and low birth weight from maternal flu is pretty clear, though.

          • Dr Kitty

            The studies were based on higher rates of schizophrenia in Spring and Autum babies ( depending on the hemisphere). The hypothesis is that maternal upper respiratory viruses/ flu/fever in the first trimester results in brain changes that increase the risk of schizophrenia.

          • Mishimoo

            That was my take on it too, same with the one that appeared to link maternal influenza with increased risk of bi-polar disorder. I managed to find the press release, it seems that even more has been found since I first heard of the potential link with schizophrenia – http://www.nimh.nih.gov/news/science-news/2013/flu-in-pregnancy-may-quadruple-childs-risk-for-bipolar-disorder.shtml

    • moto_librarian

      I rarely can formulate a witty comeback in real time, but I would love to ask this CNM the following: “So you would prefer that my unborn child and I risk death from the flu rather than autism? Or do you just not care about the health and well-being of all of the other patients in your practice?”

      This is inexcusable. Write that complaint, and if she isn’t reprimanded, I would start looking for a new practice.

      • Sue

        Not only does influenza during pregnancy increase the risk of miscarriage, but pregnant women can have a severe pneumonitis from some strains of influenza. Two potential victims.

    • DiomedesV

      Aside from the absurdity of the suggestion that you not get a flu shot, there’s the implicit suggestion that it would be understandable if you blamed yourself in any way for your son’s autism. That’s completely unacceptable. I think you should file a formal complaint.

    • Medwife

      I would just… I don’t even know what I would do in your shoes. I’d probably leave that practice. I think that would be a deal breaker for me. If you make a complaint and try to get across why what she said was SO wrong, you’d be doing a good deed, but I would understand if you don’t want to put yourself through it.

      How I handle women who don’t want the flu shot? First I try to gauge if their reluctance is lack of knowledge or hard core suspicion of modern medicine. I go out of my way to give info to the patients who lack knowledge. To be honest with the hardcore suspicion people, I don’t go overboard with immediate response. I say there is a lot of evidence of the safety and beneficial effects of the flu vaccine in pregnancy and that I encourage all my pregnant patients to get one. And drop it. Ideally I will see them several more times and build trust over those visits before revisiting the issue again. But I know the odds are against my persuading them.

    • rational adult

      Update: I wrote a formal complaint. I will drop it off at patient relations today when I go for my monthly OB appointment. I considered leaving this practice but I prefer to stick with my current OB. My first pregnancy was difficult and I built a strong relationship with my OB. I also wanted to say that I’ve treated over the years with two other CNMs at this practice and neither of them were ever inappropriate in any way.

      The spurious link between autism and vaccines has come up many times since my son’s diagnosis. I was naive at the outset to think that that whole idea had gone by the wayside. So many specialists and leaders in the field have taken the time to sit down with me and begin the discussion of why we should continue to vaccinate our son. So much time and energy must be devoted to this debunking. As for the actual cause of autism, my husband and I discussed that the only way to avoid having another autistic child would be to not have another child. Thus we have accepted that risk. And having decided to have another child, to me it was a natural step to go to CVS for my flu shot the same day I bought my prenatals and my pregnancy tests.

      • Trixie

        Wow. That’s stunning. Good for you for filing a complaint.
        Probably the last person she told that to went on Facebook and posted about how even her doctor’s office says the flu shot causes autism.