“Canaries in a coal mine” is a phrase often bandied about in connection with possible causes of autism, the neurodevelopmental disorder now estimated by the Centres for Disease Control (CDC) to affect 1 in 68 children.
Proponents of the “canary” concept suggest that, like the canaries used to check for lethal gases in early 20th century coal mines (the delicate birds would succumb first, alerting the miners to the danger), children predisposed to autism may be especially sensitive to chemicals in our increasingly polluted environment, showing symptoms long before the general population starts to get sick.
Does the evidence support this idea?
For autism, environment as important as genes
While the exact cause remains elusive, the current consensus from the autism research community is that some children are born with a genetic predisposition for the condition, which may then be triggered by environmental factors.
Whereas experts once believed that autism was likely mostly hereditary, environmental factors are proving to be much more important than previously thought.
In fact, the largest study yet to examine how autism runs in families, conducted on 2 million Swedish children in 2014, suggests that the influence of genes and environment in developing autism is about 50-50.
By “environmental factors” scientists aren't only referring to toxic chemicals we're exposed to in the modern world through pollution and medications, but also to other influences apart from our inherited DNA. Such potential risk factors include, for example, infection during pregnancy and injury to the unborn baby's brain.
Read: Flu, fever in pregnancy tied to autism risk
Nonetheless, there has been a growing number of studies in recent years suggesting links between autism and environmental toxins.
The importance of environmental factors got a further boost in 2014 when another large study, this time by the University of Chicago, examined medical records from more than 100 million people in the United States to find a link between foetal exposures to environmental toxins and autism.
Read: SA Professor says we can blame the rise in autism on evolution
The study looked at genital malformations in baby boys likely to be caused by environmental exposures in the womb. The researchers found that a 1 percent increase in such birth defects was associated with an average increase of 283 percent in cases of autism.
In a nation-wide US Nurses Health Study in 2013, researchers found strong evidence that exposure to high levels of air pollution during pregnancy, such as living near a freeway, can increase the chance that a child will develop autism. The results supported those of previous studies suggesting this link.
Pesticides have also been linked to autism in several studies. In one of the most recent, a 2014 study by researchers at the University of California, pregnant women living near farms where pesticides were applied had a two-thirds higher risk of having children with autism.
‘Canary’ analogy should be used with caution
Although the evidence for environmental risk factors for autism is certainly mounting, experts stress that strong links between specific chemicals and raised risk has been made in only a few cases. One such example is valproate, a drug used to treat epilepsy, which has been shown to raise risk for autism spectrum disorder by three times in children of mothers who take it during pregnancy.
Even in such seemingly clear-cut cases, a direct causative link has not been shown.
Thus the “canary in a coal mine” concept, while compelling, and useful to highlight the potential dangers of a toxic environment, has yet to be definitively proved.
It has unfortunately also been adopted by certain groups and commentators who use it to promote the notion that vaccinations are a cause or risk factor for autism – a notion thoroughly discredited by the conventional medical community.
Statement on The Canary Party's FaceBook page indicative of anti-vaccination
Dr Susan Malcolm-Smith of the Autism Research Group at the Department of Psychology, University of Cape Town, confirms that their stance on the issue reflects that of most reputable medical bodies, including the CDC and World Health Organisation i.e. that there is currently no evidence to support a link between vaccination and raised risk of autism.
Read: Measles surges in UK years after vaccine scare
Protecting against environmental risks
The advocacy organisation Autism Speaks recommends the following precautions especially for women who are pregnant or trying to conceive (although they are sensible steps for anyone to take):
- Discuss any medications and supplements you are taking with your doctor. With regard to autism in particular, discuss risks associated with terbutaline (a drug sometimes prescribed during pregnancy to prevent premature labour), valproate, over-the-counter painkillers, prenatal vitamins, antipsychotics and mood stabilisers. Also ask your doctor about folic acid supplementation – research suggests this reduces the risk for autism.
- Don't smoke or drink alcohol, and avoid smoky environments.
- Eat plenty of fresh, unprocessed fruit and vegetables but wash it thoroughly to reduce possible pesticide or microbial contamination.
- Cut down on packaged foods. Some packaged foods – such as microwave/oven-ready meals – leach chemicals into food. These chemicals can include endocrine-disrupting chemicals such as BPA and phthalates.
- Expert opinions differ on how much fish pregnant women should eat, but two servings a week of fish low in mercury is a good compromise between getting the excellent nutrition fish provides and limiting exposure to toxins.
Read: The catch-22 of eating fish
- Limit use of personal care products (moisturisers, body wash, perfume, etc.) with strong scents and artificial ingredients.
Read: More tips on cutting down on cosmetics
- While pregnant or breastfeeding, reduce or avoid exposure to fumes from new furnishings and cars; pesticides, fungicides, fresh paint or solvents. Avoiding these products will reduce exposure to potentially toxic chemicals such as perfluorinated compounds (PFCs).
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Image: Autism Day from Shutterstock
Olivia Rose-Innes is Health24’s EnviroHealth Editor. Read more of her columns and articles or post a question to her expert forum.