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20-04-2006 | Thyroid | Article

Sunscreens may induce hypothyroidism


Meeting website

UV-absorbing chemicals found in sunscreens may disturb production of thyroid hormones, German scientists have reported at the European Congress of Endocrinology in Glasgow, UK.

"We may have to rethink how we protect children and those with existing thyroid problems or those in iodine-deficient areas from sun exposure," say the researchers led by Josef Köhrle, from the Charité University in Berlin.

For their study, the team treated 2-month-old female rats with the endocrine active compound 4-methylbenzylidne-camphor (4MBC) for 5 days. The chemical is used as an UV absorber in sunscreens and other cosmetics such as anti-ageing creams.

The investigators found that after 5 days, there was a significant, more than two-fold increase in serum levels of thyroid stimulating hormone (TSH) in the rats that received 4MBC at concentrations exceeding 33 mg/kg birth weight, while levels of thyroxine (T4) were slightly decreased and levels of triiodothyronine (T3) remained unchanged.

The serum data obtained are consistent with early stage hypothyroidism, during which time the peripheral organs maintain normal serum T3 levels, Köhrle et al told delegates.

In addition, the weight of the thyroid glands of the rats was remarkably increased after 5 days of treatment with 4MBC, at concentrations exceeding 33 mg/kg birth weight.

"These results indicate that 4MBC is a potent inhibitor of the pituitary-thyroid system in rats," the investigators summarize.

In conclusion, Köhrle cautioned: "These are initial studies which show that UV-absorbing chemicals in sunscreens have an effect on animals, so we need to test these findings in humans before coming to any safety conclusions. We also have to bear in mind that sunscreens have a beneficial effect in protecting against skin cancer."