Can rain cause autism?

There are a lot of different theories about what causes autism, but not much consensus of opinion. In recent years, vaccination has been mooted as a potential cause of this condition, but so have lots of other things including pre-natal ultrasounds, wireless technology and certain environmental toxins. This week another potential cause of autism was added to the list: rain. Research published in Archives of Pediatric and Adolescent Medicine has found that in the USA, autism is more common in parts of the country where they have the most rain [1]. The results were highly significant from a statistical point of view. And the potential impact appeared to be large. The authors of the study estimated that elimination of the ‘rainfall factor’ would cause autism prevalence to fall by 33-43 per cent (a lot).

Epidemiological studies of this nature are not good for proving cause and effect. In other words, we cannot tell from this study that rain causes autism, only that it’s associated with it. The authors of the study suggest a number of explanations for the association though. These include:

1. In rainy areas, kids are less likely to go outside and more likely to stay in watching TV. TV viewing in young children has, apparently, been linked to what the authors describe as psychopathological characteristics, including problems with language development and behaviours consistent with attention deficit hyperactivity disorder (ADHD).

2. Staying indoors might, through reduced sun exposure, lead to relatively low levels of vitamin D. Vitamin D is important for the production of the chemical calcitriol, which is important for brain development.

3. Staying indoors puts children at risk of increased exposure to household chemicals that might play a part in the development of autism.

Of course one other possibility is that rain is actually causing autism. Not the water part of rain, of course, but something that may come with it. The stand-out suspect here is the heavy metal mercury.

While the authors of the study do not mention mercury specifically, they cite a study in support of their theory that environmental toxins may cause autism which focused on the potential role mercury plays in autism. This study found a significant link between mercury released into the environment and rates of autism [2].

One person who has looked at the potential mercury/autism link more closely than perhaps anyone else is David Kirby, a journalist and author of Evidence of Harm. You can read Kirby’s take on the recent rainfall study here.

The authors of the rainfall study admit their study does not prove that the existence of an environmental trigger for autism, but say that their results are consistent with this idea. They add that further research into whether such a trigger exists is warranted. At the current time, we don’t know whether rain can cause autism or not. But the fact of the matter remains that through the delivery of mercury or some other toxin(s), it might.


1. Waldman M, et al. Autism prevalence and precipitation rates in california, Oregon, and washington counties. Arch Pediatr Adolesc Med. 2008;162(11):1026-34.

2. Palmer RF, et al. Environmental mercury release, special education rates, and autism disorder: an ecological study of Texas. Health Place. 2006;12(2):203-9.

16 Responses to Can rain cause autism?

  1. Anna 6 November 2008 at 2:14 am #

    The non-profit Vitamin D Council has some interesting info on treating autism with Vit D, after some have noted worsening symptoms in the winter.

    www dot vitamindcouncil dot org

  2. Anne 6 November 2008 at 12:06 pm #

    My son is autistic (Asperger’s syndrome) and I find these kinds of studies almost an insult. My son was born with autism. All people with autism are born with it. The fact that it doesn’t always become apparent until around 18 months old is simply that that is when the social and communication deficits of autism become most apparent.

    My son was ‘different’ from the day he was born, but in hindsight I can say that the first signs of autism appeared when, from the age of only 11 weeks, he would scream with fear if anyone, other than myself or my husband, came near him. He would become terrified and would not be consoled. At the time I thought he must have had the normal stranger fear that nine month old babies often get and that he was simply amazingly advanced…..I was proved wrong when this fear of other people continued…..even to an extent now at the age of nearly 20 years. Other autistic symptoms developed as my son developed.

    Autism has always been around but how people see it has changed. It is also being more readily diagnosed. Just 30 or 40 years ago many children with it would have been diagnosed as having a “personailty disorder” or “schizoid” personalities or “emotionally fragile”, or the high functioning ones simply ignored as eccentric loners.


  3. Dr John Briffa 6 November 2008 at 12:31 pm #

    Your experience was that your son was “different” from the day he was born. Are you open to the fact that other people may have had a different experience? Say, that they felt their child was developing normally and exhibiting “normal” characteristics for their age, only to (perhaps quite suddenly) regress into autism at some point?

  4. Anne 6 November 2008 at 1:48 pm #

    Hi John,

    Yes I am open to the fact that other people may have a different experience, one that they think their child was developing ‘normally’ and then regresses, but I’m not different than that myself. I thought my son was amazingly advanced in his development, I thought his ‘difference’ was, in fact, a sign of genius ! Everybody who saw my son during his first few weeks said he was the most amazingly alert baby they’d ever seen ! It’s only with hindsight that I can say these were early signs of his ‘different’ brain development which would later be diagnosed as autism. I would say that even when it appears that a child has been developing ‘normally’ and then regresses it is still that the child had autism from the start but that it did not show itself until he/she reached a particular developmental stage. For example when it comes to speech which some parents say their child was doing ‘normally’ and that they suddenly stop at 18 months…..that is the age at which speech stops just being words spoken and becomes a social thing, I don’t know if I’ve explained that very well, but that’s when the autistic child who was saying words stops talking.


  5. Anne 6 November 2008 at 2:18 pm #

    Hi John,

    Some analogies I’ve just thought of…..babies who are born either blind or deaf, this is not always apparent straight away, the child may be one or more before this is diagnosed. Deaf babies still make the ‘normal’ sounds that hearing babies make for quite a while. What if a child had something wrong with their spinal cord which meant they couldn’t walk, this might not show itself until the developmental stage when a normally developing baby would start learning to walk, the child with that kind of disability wouldn’t and so would get diagnosed then, not when they were younger.

    Autism is very complicated and not enough is known about it really, but you’ll often find that siblings have it or that parents or other near relatives have traits of it. I would bet that autism is genetic.


  6. Dr John Briffa 6 November 2008 at 2:25 pm #

    This is not meant to dismiss your opinion, but there is a legion of parents and plenty of psychologists/paediatricians who believe that autism can be truly regressive (essentially normal child one moment, then not later). And if this does reflect reality, then it’s likely that there’s one or more environmental trigger for the condition (including, potentially, rain/mercury exposure). I would suggest that many would see this sort of research not as “almost an insult”, but needed and important.

  7. Anne 6 November 2008 at 3:12 pm #

    Hi John,

    I don’t dismiss research into autism and it’s causes, not at all, but rain as a cause seems to suggest they’re not doing their research work hard enough ! Another area of research which is even more important, though, is how best to help autistic children.


  8. MinorityView 7 November 2008 at 3:23 pm #

    The MMR didn’t and doesn’t contain mercury. There is a theory that children who are already ill from mercury exposure might be unable to cope with three live (although attenuated) vaccines at one time. In real life no one goes through measles, mumps and rubella within one month.

    quote: . There is thimerosal (mercury) in the MMR: (False) Thimerosal, an ethylmercury compound, is not and never has been an ingredient in the MMR.

    A simplified list of the MMR-II ingredients are as follows (more specifics can be found in the MMR-II manufacturer’s insert):

    Amino Acids,
    Bovine Albumin or Serum,
    Chick Embryo Fibroblasts,
    Human Serum Albumin,
    Phosphate Buffers,
    Sodium Chloride,

  9. Hilda 7 November 2008 at 8:56 pm #

    When I was pregnant one dentist said that I needed to have many of my amalgam fillings changed. This would of course have meant drilling the old ones out. He thought he was on to a good thing as pregnant women do not pay. I went to another dentist and he disagreed, However I did not know then about the mercury toxicity. Thank goodness I kept my fillings but I warn other mothers to be careful about this.

  10. Jenny 8 November 2008 at 12:19 am #

    It is interesting that some research points to mercury as a trigger for autism
    Wasn’t mercury a component of the MMR vaccine, and could it be that element that was connected to autism development rather than the MMR element?

  11. Kevin eakins 8 November 2008 at 12:49 am #

    Mercury toxicity is transgenerational. It breaches the placental barrier. Therefore if the pregnant mothers body has mercury this is deposed in the body of the growing foetus. In fact unfortunately it seems that mercury can be said to be deposited in HIGHER concentration in the new-born-to-be (ie: the process of deposition is highly “effective”). Therefore the unborn babies of pregnant women eating large amounts of mercury laden food, having many amalgam fillings, and now possibly it seems living in an area with mercury laden rainfall are at risk of receiving more the their fair share of mercury. As frightening as this study may be it comes as no surprise to me. In other words there is no contradiction between a child being born with autism and envrionmental factors that emphasize higher than average levels of the most toxic (by a mile) commonly found metal on earth.

  12. Kerry 8 November 2008 at 2:20 pm #

    I have a son on the autistic spectrum, and like Anne, my son was definately born with autism. Although i was a first time mum, I could see that my son’s behaviour was completely different from all the other babies I knew.

    However, as my baby grew i had some “lucky breaks”. At age 6 months he was taken off of cows milk due to diahorreah – and this lead to marked improvements in his bevaviour.

    At age 3 he wasn’t making eye contact, he would just sit and compulsively suck each of his fingers in turn, and scream the house down if I left his sight. One night (on account of bad eczema on his face), i put a max epa capsule in his bedtime drink. The next morning it was like somebody had switched on a lightbulb – he was making eye contact and started talking shortly after. Since then my accidental discovery that fish oil really helped my son, has been validated by research.

    Simon Baron-Cohen, a reknown autism specialist, has a theory that there is an autistic spectrum and that we are all along there somewhere. This makes sense to me, but I would further speculate that environmental factors can increase or decrease the likelihood of autisic tendencies expressing themselves.

    My own experience would bear out both Anne’s experiences, and the results of this trial. Some children are no doubt born autistic from day one, but the condition can be drastically improved by maniulating environmental factors. Just as other children are born probably more towards the “normal” side of the autistic spectrum but as time goes on are exposed to environmental conditions which push them into expressing autistic tendencies and/or regressing along the developmental path.

  13. Anne 8 November 2008 at 3:55 pm #

    Hi Kerry,

    My son was breastfed, he never had cow’s milk and he wouldn’t move on to solid foods when other babies did. When he was two years old he was still largely subsisting on breast milk with a banana or so per day…he was extremely healthy ! Shows how good breast milk is. He didn’t wean until he was five years old.

    I haven’t noticed any particular foods that make the expression of my son’s autism worse, but I have noticed that certain situations do, notably social situations and change. Unpredictable change can affect his behaviour for months and years. For example he had a norovirus one day when he was 14, he threw up only the once, but for years after and still to this day he is paranoid about getting ill and has a lot of contamination fears, handwashing compulsions, checking foods minutely and if they look the slightest bit ‘different’ throwing them away.

    My son also would never have been able to cope with school, too many people, too much noise and sensory stimulation, so we home educated him instead and I’m sure that that was one of the most helpful things we have been able to do for him. I contributed a chapter to the book ‘Home Educating our Autistic Spectrum Children, paths are made by walking’ edited by Terri Dowty and Kitt Cowlishaw. Simon Baron-Cohen wrote a bit on the book.

    all the best,

  14. robert 8 November 2008 at 7:55 pm #

    From fairly extensive readings on vitamin D, it seems to me very possible that one important factor in causing autism could certainly begin in the womb baby if the mother is deficient in vitamin d, e.g., very little sunshine during pregnancy from sept thru to may. The original recommended levels of vitamin D supplementation seem to be woefully low, with vit D supplements now being recommended during winter pregnancy, and baby/infant supplementation may also soon be reviewed upwards in view of all the recent research.

  15. Elizabeth 9 November 2008 at 1:14 am #

    Dear Anne, I accept the reality of your situation and I hope you can do the same for me. In 1990 I gave birth to boy/girl twins. At fifteen months they were given the original MMR and within the next month I watched as my daughter lost eye contact with us, lost her developing speech totally, withdrew into herself and started to throw objects with no regard for the safety of herself or others (she had previously met all her developmental milestones). Her twin brother remains unaffected and hopefully will go to university next Autumn while his twin sister with High Functioning Autism is unable to stand the stress of a formal academic education. She struggles to make sense of a world that, to her, is puzzling in the extreme. The contrast between them is too cruel for words.

    More than ten years ago I explained my belief that the MMR had either caused or triggered my daughter’s descent into regressive autism to a locum doctor attending my son and was told, “you’re an intelligent woman, Mrs Q, you know this sort of thing happens”.

    My personal belief is that what we call “autism” will end up being referred to as “autisms” because they are multi-causal and multi-factorial in nature. If the orthodox medical profession were listening to parents then by now clinical research would’ve been carried out on children who descended into regressive autism and we would know, for example, which children were not suited to receiving triple or multiple vaccines and which children were genetically not able to excrete mercury efficiently. Strangely, as far as I can ascertain, there’s been little or even no attempt made in the UK to carry out clinical research on children who descend into regressive autism – now why would that be?

    Lastly, living by the seaside, I’ve observed that the air coming in on the Atlantic westerlies is much cleaner than the air we get from the Continent on the easterlies. It’s also been observed in the USA that children who live downwind from a coal-burning power station are more likely to be diagnosed with autism than those who live more distantly.

  16. Birgit Calhoun 21 July 2009 at 2:03 am #

    There is a good chance that the lack of sunshine and therefore Vitamin D deficiency causes autism because Vitamin D deficiency results in a lack of glutathione that is essential in mercury and other heavy metal detoxification. So if a person was exposed to, let’s say, mercury and lives in an area lacking in sunshine that is essential for Vitamin D, it is entirely possible for mercury toxicity to become a major factor. There are some genetic factors that might come into play as well.

    As to Anne’s comments, I would like to say that the chid may have had autism since birth, but he or she may have acquired it through the mother, especially when the mother is Vitamin D deficient or lives in an area with high rainfall.

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