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Is your soap hurting your thyroid function?

posted Aug 1, 2010, 5:14 AM by Medhavi Jogi   [ updated Aug 1, 2010, 9:56 PM ]

In the last few months there have been increasing news reports that antimicrobial soaps act as endocrine disruptors and have a harmful impact on endocrine function. Endocrine disruptors are natural and man-made chemicals that can either mimic or disrupt the action of hormones. Their impact on human biology is still unclear, but they have been implicated in a number of reproductive and health problems in animals. The active ingredient that is under question is triclosan. Apparently the FDA has been doing studies on this issue for some time, but what prompted all this? 

Well, looking back into the published medical literature on this, there is an interesting chronology that has lead up to this debate. Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) is a chlorinated phenolic antibacterial compound that is widely used in soaps, toothpastes, cosmetics, fabrics and plastics (1) , typically at a concentration of 0.1–0.3% (2) . The structure of triclosan is similar to bisphenol A and dioxins (3) , and it is degraded into various chlorinated dibenzo-p-dioxins by heat and ultraviolet irradiation (4) . The reason this compound is used in soap is for its broad spectrum antibacterial and antifungal action which is accomplished by blocking lipid synthesis by specifically inhibiting the enoyl-acyl carrier protein reductase (ENR or FabI) (5) in both prokaryotic and eukaryotic cells (6). Since the substance is so abundantly used, it is measurable in the water we drink and therefore some can be detected in human blood. In fact, it was detectable in 75% of urine samples in the US National Health and Nutritional Examination Survey in 2003–2004, with higher levels in individuals with the highest household income.(7) Because triclosan is present in such a variety of personal care and household products, in the ecosystem, and in human body fluids, there is a potential concern for adverse effects on human health. 

The story gets interesting between 2002 to 2006 when it was shown to bioaccumulate and have endocrine effects in fish and amphibians (8) Studies in frogs and rats showed reduced production of the thyroid hormones T3 and T4. TSH values were not shown to have been effected. (9) Although interspecies differences exist, effects on the thyroid of this magnitude, particularly T4, should be carefully evaluated because the thyroid hormone status in a pregnant women seems to have sustained neuropsychological effects on the child after birth.  The effects on human thyroid endocrine function on not entirely clear. Awareness of endocrine disruptors has increased in the last few decades regarding common environmental exposures may affect thyroid function in humans and other species. Individuals may be most vulnerable to these effects in utero and in infancy, when thyroid hormone is needed for normal neurodevelopment. The list of endocrine disruptors of the thyroid is long and can be categorized based on the negative effects they have on different aspects of thyrod hormone function. : (11)  Use the thyroid glossary if some of the terms are unfamiliar.

Reduce thyroid perioxidase activity:  
    •   Isoflavones
Compounds that decrease T4 half life by decreasing T4 clearance:      
    • pesticides, dioxin, furans
Reduce the ability of the thyroid to uptake iodine:      
    • perchlorate, thiocyanate, nitrate
Inhibit transport of thyroid hormone in the blood: 
    • polybrominated diphenylethers  (PBDE's), Hydroxylated Polychlorinated biphenyls (PCB's)
Inhibition of peripheral T4 to T3 conversion
    • sunscreens, styrenes
Have direct effects on peripheral tissue thyroid hormone receptors: 
    • PCBE's, PCB's, isopropylidenediphenol or bisphenol-A  (BPA), Triclosan


References
  1.  McMurry et al., 1998
  2.  Sabaliunas et al., 2003
  3. Cabana et al., 2007
  4. Kanetoshi et al., 1987
  5. Heathet al., 1999; Newton et al., 2005
  6. Guillen et al., 2004; Lygre et al., 2003; Villalain et al., 2001
  7. Dayan, 2007, Calafat et al., 2008
  8. Adolfsson-Erici et al., 2002; Foran et al., 2000; Ishibashi et al., 2004; Veldhoen et al., 2006
  9. Veldhoen et al., 2006; Crofton et al., 200; Zorrilla et al. 2009
  10. Haddow et al., 1999; Morreale de Escobar et al., 2000
  11. Pearce and Braverman et al. 2009


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