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