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 K?hrle (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 K?hrle 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.

(1) Up to 5 % of the UK female population may have mild thyroid failure (asymptomatic).This group may find themselves affected by the work described here. In a UK context, this may represent 1.5 million women. Women are three to four times more frequently affected by thyroid problems than men.

(2) Some moderate exposure to daylight is useful to stimulate production of Vitamin D, however excessive exposure to sunlight can lead to skin cancer.

Professor Josef K?hrle presented the following papers at the European Congress of Endocrinology on 2nd and 3rd April:

(1) 4-methylbenzylidene-camphor (4MBC) causes pituitary effects comparable to hypothyroidism
IH Hamann1, C Schmutzler1, P Kirschmeyer2, H Jarry2 & J K?hrle1
1Charit? - Universit?tsmedizin Berlin, Berlin, Germany , 2Universit?t G?ttingen, G?ttingen, Germany.
Click Here For Abstract.

(2) The UV filter benzophenone 2 inactivates human recombinant thyroperoxidase in vitro and disturbs thyroid hormone homeostasis in rats
C Schmutzler1, A Bacinski1, P Ambrugger2, H Klammer3, W Wuttke3, A Gr?ters2, H Jarry3 & J K?hrle1
1Institut f?r Experimentelle Endokrinologie, Charit? - Universit?tsmedizin Berlin, Berlin, Germany , 2Institut f?r Experimentelle P?diatrische Endokrinologie, Charit? - Universit?tsmedizin Berlin, Berlin, Germany , 3Experimentelle und klinische Endokrinologie, Universit?ts-Frauenklinik G?ttingen, G?ttingen, Germany.

endocrine-abstracts/ea/0011/ea0011p429.htm

The European Congress of Endocrinology takes place at the SECC in Glasgow from 1-5 April, 2006. This will be the biggest hormone conference in Europe in 2006, with 2200 delegates and almost1200 pieces of original research.

euro-endo/ece2006/welcome.html