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IODISED salt may have caused a drop in men鈥檚 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鈥檚 average
date of birth was 1924鈥攚hen iodised salt was introduced in America.

To test the link, Crissman鈥檚 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. 鈥淭hey
ended up with testes twice as big as normal,鈥� says Crissman.

Richard Sharpe of the Medical Research Council鈥檚 Reproductive Biology Unit in
Edinburgh says there are cases of men with underactive thyroids having enlarged
testicles. But he is sceptical: 鈥淪perm count data are so variable.鈥� And Crissman
warns against cutting down on iodine. 鈥淭here鈥檚 a danger people could get exactly
the wrong message and decide that sperm counts are more important than brain
诲别惫别濒辞辫尘别苍迟.鈥�