Most of us know about hyperthyroidism - where the thyroid gland becomes over-active - but how many know about the opposite condition, hypothyroidism? It's even more common, and yet most sufferers don't even know they have the problem.
Typical symptoms include tiredness, aches, constipation, putting on weight (or being unable to take it off), feeling cold, and being generally sluggish.
The reason for the recent large increase in hypothyroidism is down to the gradual reduction of iodine in our diets, says nutritionist Ingrid Kohlstadt. People have also been avoiding iodine-rich foods, such as salt and eggs, for health reasons, while many processed foods also contain less iodine.
She also blames the rise of soy-containing foods, which affects healthy thyroid function.
The remedy is fairly simple, she says. Once an iodine deficiency has been detected, and provided it's not too severe, the patient can reverse the problem with a self-help programme that involves stop eating soy products, consuming more iodine-rich foods, and supplementing with iodine and selenium.
(Source: Townsend Letter, 2008; 305: 112-3).