4-methylbenzylidene-camphor (4MBC) causes hypothyroidism
http://www.endocrine-abstracts.org/ea/0011/ea0011oc60.htm
4-methylbenzylidene-camphor (4MBC) is an endocrine active compound used as an UV absorber in sunscreens and other cosmetics such as anti-aging lotions and day care products...
Additionally, 4MBC can be resorbed through the skin (Janjua NR et al. 2004 J Invest Dermatol. 123:57–61).
Society for Endocrinology 03.04.2006
Chemicals in sunscreens may disrupt thyroid hormones
UV-absorbing chemicals used in sunscreens may disturb production of thyroid hormone, according to new work being presented at the European Congress of Endocrinology in Glasgow.
German researchers looked at rats exposed to the UV-absorbing chemicals 4MBC (also used in some anti-aging creams) and benzophenone 2 (BP2).
They found that after treating the rats with 4MBC for 5 days, the levels of thyroid stimulating hormone were significantly raised (with the other main thyroid hormones T3 was unchanged, while T4 was slightly decreased).
Research leader Professor Josef Köhrle (Charite University, Berlin), said:
This change in thyroid hormone levels is typical of the early stages of hypothyroidism. In addition to changes in hormonal levels, we also saw a significant increase in the weight of the thyroid glands. These results indicate that 4MBC is a potent inhibitor of the pituitary-thyroid system in rats.
The group also screened human cells for the effect of the UV filter benzophenone 2 (BP2), and found that it inactivated a key enzyme involved in thyroid hormone production, but these effects were prevented where there was an adequate amount of iodine in the reaction mixture. They later replicated this effect in rats.
Professor Köhrle commented:
These are initial studies which show that UV-absorbing chemicals in sunscreens have effect on animals, so we need to test these findings in humans before coming to any safety conclusions. We also need to bear in mind that sunscreens have a beneficial effect in protecting against skin cancer, and so the last thing I’d say to anyone just now is to stop using sunscreens, but less extensive direct sun exposure might be better, too!
MBCs have been found to be accumulating in the environment, eg in lakes in Switzerland, and we believe that this is a result of sunscreen use. The work has shown that MBC and BP2 are potent disruptors of the pituitary-thyroid hormonal system in rats. It’s early days, but if the same effect is discovered in humans, then we may have to rethink how we protect children and those with existing thyroid problems or those in iodine-deficient areas from sun exposure.
Weitere Informationen: www.euro-endo.org/ece2006/welcome.html
http://www.innovations-report.de/html/berichte/biowissenschaften_chemie/bericht-57403.html
The group also screened human cells for the effect of the UV filter benzophenone 2 (BP2), and found that it inactivated a key enzyme involved in thyroid hormone production, but these effects were prevented where there was an adequate amount of iodine in the reaction mixture
OK.. so the second effect can be prevented by addition of iodine to the mixture, but if not...
a LOT of the world, Australia included is low in iodine levels.
These chemicals probably partly contributed to my hypothryoidism together with low levels of iodine.(although I covered up instead a lot of the time).
I was on iodized salt, but I didn't eat much salt at all...avoided usually salt altogether. I didn't particularly like the flavour of it.
In the "old" days when milk was delivered in bottles, some iodine was provided by the residue left on washing the bottles with iodine for re-use apparently I've read somewhere..
now studies are showing low population levels.. one on school children in Sydney, in soil tests around Canberra.. I think.. must check on source ? It is due to our "ancient" soils having lost their iodine.
I was looking thru my wallet yesterday and noticed a picture taking my the computer lab at Tafe back in 2001.. before I went on thryoid hormones. I looked tired and skinny.. but the bottom half of my nck definitely was a hard and swollen... and I'd been complaining for decades of a choking feeling and a lump ..and inability to breathe due to this lump, a cough at night to be able to get oxygen.... NOw I can see the difference in my neck..Why couldn't the docs I went to back then?
I also have breast cysts and now an ovarian cyst too....I need to find out more on iodine. I suspect cutting iodized salt, supplements containing any iodine, and kelp from my diet may have been a mistake. Of course too much is bad in promoting antibodies too maybe(correlation maybe observed in US).
Update:
Elaine Has a thread on sunscreens
http://forums.about.com/n/pfx/forum.aspx?msg=4425.1&nav=messages&webtag=ab-thyroid2#a1