Fig. 1

Historically, goitre has been common in highland areas where it could become endemic. This is mainly because the soil is poor in iodine but another mechanism may also be in play. Endogenous generation of nitric oxide (NO) is exceptionally high in highlanders due to continuous high activation of endothelial NO synthase (eNOS) in response to the low oxygen at these altitudes. In the body NO is rapidly converted to nitrate (NO₃⁻), an anion known to compete with iodide (I⁻) for uptake in the thyroid gland. Here we propose that the high susceptibility to goitre in highlanders may be partly related to the persistently high endogenous formation of NO and nitrate in these populations