Tuesday, November 20, 2012

The precautionary principal in the garden of obesogens

*Safe* water bottles?
Creative Commons image

Today's post is a follow-up to the previous post on the pervasiveness of environmental contaminants and pollutants and the potential link to obesity, particularly in utero. As I left off, much research remains to be conducted to definitively link specific industrial chemicals (known endocrine disruptors), which are highly prevalent in our society, to obesity.

The precautionary principal is used to protect public health and has various interpretations. In general, it says that complete evidence of harm does not have to exist before steps can be taken to protect members of society from harm (Weir et al, 2010). In this post, I'd like to discuss a Canadian-specific framework for applying the precautionary principal in relation to suspected obesogens, public health, environmental health, and our overall North American lifestyle.

 Historically, there has been a general failure in North America and Europe to determine potential negative public health and environmental effects from industrial chemicals before manufacture and widespread use (Wordsworth et al, 2007).  This likely explains why every person or animal that has ever been tested has had detectable levels of endocrine-disruptors in their bodies.
"An analysis by the Environmental Protection Agency in 1998 found that, of the 3,000 chemicals that are used in the highest volumes in the United States (3), forty-three per cent had no testing data at all that would establish their basic toxicity. Only 7 per cent had a full set of safety tests (4). For chemicals used in lower volumes, even less information was available (5)." (Wordsworth et al, 2007).
The European Union is no better. And we Canadians don't have a lot to be proud of either:
More recently, in September 2006 the Canadian government concluded one of the most extensive reviews of substances ever undertaken. The government identified more than 4,000 suspect chemicals in Canada with the potential to be persistent, bioaccumulative and “inherently toxic” (8)." (Wordsworth et al, 2007).
Does this mean that the precautionary principal is not relevant? If the link between certain endocrine-disruptors and obesity is found to be causal, is it already too late? I think it's a no to both, but truly unfortunate to have to put ourselves in this situation in the first place. Applying the principal, particularly when it has to do with the environmental sector and public health, is far from straightforward, as you will see.

Weir et al (2010) propose a framework for applying the precautionary principal in Canada (10 Guiding Questions). There are two parts. The first assesses the degree of certainty to which the relationship between a risk (in this case certain chemicals) and harm (obesity and other potential health outcomes) can be considered causal. They use Sir Bradford Hill's 9 criteria for causation. Anybody with an epidemiology background should know what these are. I'm not going to list them here, simply because they're not really necessary for what I am going to talk about. What I am interested about is the second part, the remaining 9 questions, and Weir et al's discussion.
2. Is the harm associated with the suspected exposure serious?
3. Is the suspected exposure widespread?
4. Is there an observed increase in the incidence of the suspected harm that is temporally associated with increased exposure?
5. Is the harm associated with the suspected exposure difficult to treat or reverse?
6. What are the economic and non-economic costs and benefits of action and non-action?
7. Are the proposed control measures proportional to the level of risk? Are the economic costs of removing the exposure minimal? Are the health and societal costs of removing the exposure minimal?
8. Are comparable situations being treated similarly according to a standard of practice?
9. Is the level of the protective measures consistent with equivalent areas in
which scientific data are available?
10. If precautionary measures are adopted, is there any new evidence to reduce the level of uncertainty about harm and benefit?

Going by these questions, yes obesity is serious and yes exposure is widespread. I would say that at this point, #4 can only be answered in animal studies. Obesity has been difficult to treat and reverse and it has multiple determinants. Number 6 and 7 are where it starts to get tricky. Because obesity has multiple determinants (i.e. is complex) and because of lack of evidence, it's hard to say whether decreased use of these chemicals would result in less obesity and related diseases and therefore lower healthcare costs and other indirect costs like absenteeism/presenteeism. 

Weir et al contend that the appropriateness of applying the precautionary principal increases "when the economic and social costs of removing the exposure are small relative to the suspected harm." These chemicals no doubt make life easier for us - are we willing to give up a certain level of convenience to live without them, at least until adequate replacement substances are found (I have faith in technology to remedy this gap rather quickly)? Are we willing to knowingly gamble with our economy? I could answer for myself, but I'm sure that many others would disagree, some with valid points. 

At the same time, Weir et al add that appropriateness of applying the principal increases "when the health costs of removing the exposure are minimal; and when, in addition to the uncertain harms, there are known health, economic or social harms caused by the exposure." I can't see health costs associated with removing obesogens; worse case,  procedures with medical equipment made with obesogens are no longer possible until replacement substances are found. Obesogens also have known negative impacts on the environment and suspected health impacts that go beyond obesity. I am unaware of comparable situations that could be used to address #8 (that doesn't mean there aren't any), and we're not even close to answering #9 and #10 yet. 

This is only the tip of the iceberg. Based on this quick run-through, I hope you grasp the complexity of this problem. What do you think? Is it too late to apply the precautionary principal? Is applying the principal even relevant for obesity, or worth the potential negative social and economic effects? Is not applying it worth further environmental damage? 

Weir E, Schabas R, Wilson K, & Mackie C (2010). A Canadian framework for applying the precautionary principle to public health issues. Canadian journal of public health. Revue canadienne de sante publique, 101 (5), 396-8 PMID: 21214055