Iodised salt may have caused a drop in men's sperm counts since the 1950s, according to scientists in America. They say that iodine deficiency, while stunting brain development, also appears to boost sperm counts.
Our bodies need iodine to make the thyroid hormone thyroxine, which is vital for developing brains. But in some parts of the world crops contain little iodine. A deficiency can cause impaired mental development, so iodine is added to salt.
In the 1990s James Crissman of the Dow Chemical Company in Michigan and colleagues at the University of Illinois in Urbana looked at data showing a sharp drop in sperm levels around 1960. They worked out that the men's average date of birth was 1924-when iodised salt was introduced in America.
To test the link, Crissman's group raised female rats on an iodine-deficient diet and mated them with healthy rats. The offspring were subsequently weaned by their iodine-deficient mothers and later fed low-iodine diets. He found that the offspring had larger testicles and produced more sperm than normal rats. "They ended up with testes twice as big as normal," says Crissman.
Richard Sharpe of the Medical Research Council's Reproductive Biology Unit in Edinburgh says there are cases of men with underactive thyroids having enlarged testicles. But he is sceptical: "Sperm count data are so variable." And Crissman warns against cutting down on iodine. "There's a danger people could get exactly the wrong message and decide that sperm counts are more
important than brain development."
Author: Ian Sample
Source: Toxicological Sciences (vol 53, p 400)
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