Monday, 30 January 2012

Household chemicals and immunity

Mucky paw prints @ Paul Whiteley
Looking around most homes, it is easy to spot the modern face of physics and chemistry in action. I'm not specifically talking about microwave ovens or those other technological labour-saving gadgets like that fancy espresso coffee-maker that we seem so hooked on; but rather more humble examples like the non-stick frying pan or the variety of grease and stain resistant compounds we use to save hours and hours of cleaning and scrubbing.

Whilst it is perhaps slightly unfair to demonise all the chemicals we use - as per this article on the misrepresentation of the words 'chemical-free' - there is a growing recognition that collectively, we have not paid as much attention to the potential effects of some of these everyday substances as we should have done. I'm thinking back to older posts on things like polybrominated diphenyl ethers (PBDEs) for example.

Another case in point is this recent article by Grandjean and colleagues* linking exposure to perfluorinated compounds (PFCs) with a reduction in humoral immune response and in particular, the production of antibodies to two routine childhood vaccines. Quite a good summary of PFCs is here.

There has been some pretty widespread coverage of this paper in both the science and lay media. A summary of the research:

  • Based in the Faroe Islands, 587 children born between 1999 and 2001 were included for study.
  • Levels of several PFCs including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), were analysed from maternal blood samples taken during pregnancy alongside children' blood samples drawn at ages 5 and 7 years reflective of pre- and post-natal exposures. PFC values were subsequently compared against children's antibody responses following tetanus and diphtheria immunisation.
  • There was a relationship between levels of PFCs and the concentration of antibodies detected in that pretty uniformly PFCs were negatively correlated with antibody levels. That is a higher concentration of PFCs were associated with lower antibody response. Indeed under certain conditions, PFC levels placed children at risk of not having clinically protective levels of antibodies to these diseases. 
The potential implications of this work are pretty far-reaching although there are perhaps a few things to note. This is not the first time that PFCs have been linked to immune effects. Cord blood IgE levels correlated with PFC according to this study and those dastardly proinflammatory cytokines were connected according to this research. This and other similar research points towards immunomodulatary effects from PFCs outside of their other possible links to things like cholesterol and reproductive ability.

In terms of source, PFCs have been detected in several dietary sources particularly seafoods including fish and shellfish. Given the placement of the Faroe Islands (i.e. islands in the North Atlantic), it is not surprising that seafood is high on the menu including some more traditional dishes such as dried fish. Exposure-wise therefore, whilst the focus of the current study is on more everyday objects as being a source for PFCs, intake through food should also be kept in mind.

As with every study, replication is required. Replication not just in children (and mums) from the Faroe Islands but also from other parts of the world. A little more understanding about the relative contribution of genetics and other environmental factors influencing susceptibility might also be useful given that we all seem to be carrying at least some quantity of these compounds around with us. If the results are replicated, it is then up to the various companies and regulatory bodies to make some important decisions on the basis of perceived cost and benefit. As with many chemicals in regular use, it is not just a case of stopping production tomorrow and everything immediately changes overnight. The persistence of these compounds is such that any changes now won't really be seen for several years; the US EPA for example, estimating the serum half-life of PFOS in humans at 5.4 years.

I try not to be alarmist on this blog because ultimately these are studies which whilst providing data on association, cannot possibly take into account the wide variety of other factors potentially involved any relationship. Having said that, the evidence against PFCs is starting to accumulate from both animal and human studies. Perhaps the next time I want to fry my bacon rashers - yes, some people still do that - in healthy olive oil of course, I might just reach old skool for the non non-stick pan.

To finish, how about a little punk rock about that most sensible of floor surfaces, linoleum?

* Grandjean P. et al. Serum vaccine antibody concentrations in children exposed to perfluorinated compounds. JAMA. January 2011. DOI: 10.1001/jama.2011.2034