About 30 percent of the salt used in China's 75 counties are short of iodine, according to the Ministry of Health recently.

A survey on China's iodine-enriched salt showed that 93.8 percent of the salt used for cooking contained a required amount of iodine last year.

But there were problems in west China, where 80 counties have not carried out monitoring work over iodine deficiencies so far, said an official with the ministry.

People with iodine deficiencies are prone to suffering goitre, a swelling of the neck resulting from enlargement of the thyroid gland, which can also lead to learning disabilities.

Iodine deficiencies can also cause miscarriages of pregnant women.

"The cause of iodine deficiency is clear and easy to tackle," said the official. "The most effective way is to take iodized salt."

But some local authorities had slackened the management and supervision, leading to a rebound of diseases caused by iodine deficiencies, the official said.

He urged local governments to further strengthen monitoring work, spread the knowledge about the harms of iodine deficiencies among the public and offer them consultations on how to judge fake iodized salt.