Pesticides and vitamin D deficiency

Chemistry World, the public face of the UK Royal Society of Chemistry (RSC), carried an interesting report recently discussing research linking exposure to organochlorine pesticides (OCs) with vitamin D deficiency. The research in question is this paper by Jin-Hoon Yang and colleagues* (full-text) and before you ask, yes, it is a study of 'association', so we tread carefully.

Before wading into this study it is interesting to note that vitamin D is currently enjoying quite a trendy following in many areas. Important discussions are underway to determine whether a resurgence of conditions like childhood rickets means supplementation needs to be more closely inspected. 

I digress. A summary of the paper in question:

• An analysis of plasma levels of 7 OCs (including DDE and DDT) was undertaken for 2,337 people aged 12 and above recruited as part of the US National Health and Nutrition Examination Survey (NHANES). After exclusion of those where accompanying 25-hydroxyvitamin D (25(OH)D) were not available alongside other exclusions (e.g. pregnant women, being under 20 years old), the final participant group number was N=1275.
• The results: based across various grouping on concentrations of OCs, there were quite a few significant inverse relationships reported. That is, for the OCs -  p,p′-DDT, p,p′-DDE, and β-hexachlorocyclohexane - elevated plasma levels of these compounds individually and collectively were associated with lower vitamin D levels. Plasma levels of DDT in particular showed quite an enduring association with vitamin D levels. 
• There is a suggestion that the relationship may also be dose-dependent up to a certain point; that is up to a value of 200 ng/g lipid of DDT, vitamin D levels dropped, but increasing levels of DDT after that seemed to be linked with increasing vitamin D levels bearing in mind that most participants presented below this 200 ng/g lipid threshold.

As I said, this is a study based on association. Controlling for factors such as gender, age, race and vitamin D supplementation is an admirable quality of the study but association is normally only a guidepost to a possible relationship, not a dead cert. That and the fact that little information has been provided on why the results came out as they did, leaves the door open to further study in this area.

Noting that this blog is primarily concerned with the gut, I do wonder about these recent findings and how they may (or may not) fit into a past post on gut bacteria and organochlorine pesticides. It's a bit of a long shot but how about testing the suggestion that OCs affect gut bacteria which in turn affects other systems including vitamin D and its receptors?

* Yang J-H. et al. Associations between organochlorine pesticides and vitamin D deficiency in the U.S. population. PLoS ONE. January 2012. DOI:10.1371/journal.pone.0030093

Gut bacteria, pesticides and obesity

Although my interest in this blog centres on all things gut-related, within this huge area of research I am particularly interested in how our genetic makeup interacts with our environment and vice-versa. I suppose gastrointestinal (GI) conditions are ideally suited to this complex 'nature-nutrure' relationship as evidenced by conditions like coeliac (celiac) disease, the archetypal gene-environment condition.

An interesting paper has appeared by Hae-Sook Lee and colleagues* suggestive of an interesting 'threesome' between a species of methane gas producing microbe, organochlorine pesticides and obesity. The paper is open-access. A summary of the details:

• Fecal and blood samples from 83 Korean women were analysed alongside anthropometric (body mass index) measurements.
• Fecal levels of Methanobacteriales were quantified via qPCR and serum / fecal levels of various organochlorine pesticides (OCPs) were assayed via GC-MS among a selection of participants with detected or non-detected levels of Methanobacteriales.
• The results: Methanobacteriales were present in about a third of patient stool samples (27/83). Higher Methanobacteriales levels were present in women with a waist circumference above 83cm than below and showed some connection with elevated BMI also. Higher fecal levels of Methanobacteriales were also associated with higher serum levels of the OCPs.

We do need to take a step back from these findings before making too many associations. The sample population is quite small and the numbers of people included for analysis of OCPs for example is even smaller. Bear in mind that just looking at three primary variables is not necessarily grounds for a relationship.

I am however struck by the 'suggestion' that gut bacterial content and obesity might either increase the risk of greater take-up of compounds such as OCPs or that gut bacteria might interact with our chemical environment to potentially predispose to conditions such as obesity. This latter hypothesis: OCP levels determining Methanobacteriales levels which in turn leads to increases in anthropometric measures is the author's preferred interpretation.

The authors discuss the properties of OCPs as being central to the finding i.e. lipophilic (fat or oil loving) and also note that Methanobacteriales are quite often used to biodegrade hydrocarbons such as petroleum. I have to say I have never really thought about industrial waste management being applied to the human model but perhaps should not be so surprised given the current interest in things like industrial biodigestion.

What this study does more than anything is to reaffirm the complexity of conditions such as obesity as well as providing some new targets, environmental and biochemical, which we should perhaps be exploring with a little more assiduity.

* Hae-Sook Lee et al. Associations among organochlorine pesticides, Methanobacteriales, and obesity in Korean women. PLoS ONE. November 2011.