iodine preventing thyroid damage from sunscreens

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Study shows UV filters may disrupt hormone production

By Simon Pitman

03/04/2006-

European

researchers claim they have scientific evidence that UV-absorbing

chemicals used in sunscreens and many anti-ageing products may disturb

production of thyroid hormone in rats.

The

work, which was carried out by German researchers and is subsequently

being presented at the European Congress of Endocrinology in Glasgow,

Scotland, could be the latest in a series of consumer scares over the

effects of certain chemicals in personal care formulations.The

research team looked at rats exposed to the UV-absorbing chemicals

4MBC, commonly used in a variety of sunscreen and anti-ageing products,

together with benzophenone 2 (BP2).Accordingly, the research

team discovered that after treating the rats with 4MBC for 5 days, the

levels of thyroid stimulating hormone were significantly raised, while

of the other main thyroid hormones, T3 was unchanged and T4 was

slightly decreased. "This change in thyroid hormone levels is typical of the early stages of hypothyroidism," said research leader Professor f Köhrle from the Charite University, Berlin."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," he added.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.However,

the researchers said that these effects were prevented when there was

an adequate amount of iodine in the reaction mixture. This effect was

also later replicated this effect in rats. Professor Köhrle did

also stress that these are preliminary studies showing only the effects

on animals, adding that the next step will be to determine the effects

in humans before any safety conclusions can be drawn.He also stressed the importance of the continued use of sun care products."We

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," professor Köhrle added. MBCs

have been found accumulating in environments such as lakes in

Switzerland and the research team says it believes that this is down to

the increased use of sunscreen products in recent years. "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," professor Köhrle said.In

recent years certain chemicals have come under the microscope and have

been linked to increased rates of cancer as well as risks to the

reproductive system. Ingredients such as parabens - widely used

as preservatives, phthalates - commonly used as a softner, and

aluminium - used in certain deodorants, have brought about criticism

from consumer lobby groups worried over scientific reports that suggest

these substances could pose risks to human health.