Iodized salt does not cause thyroid cancer, which has become more common in China in recent years, health authorities announced on Monday, ahead of China's Iodine Deficiency Sickness Prevention Day that falls on May 15.

China's top health authority said on Monday that consuming iodized salt is still necessary in most parts of China to prevent any diseases related to iodine-deficiency, even though such diseases have been largely contained in China.

"There is no scientific evidence to show that the increasing occurrence of thyroid diseases reported in recent years is directly related to consuming iodized salt," the National Health and Family Planning Commission said in a statement on Monday.

"A major reason for the increase of thyroid diseases is that more people have had physical checkups in recent years. In particular, wide clinical application of highly sensitive scanning and testing devices has greatly increased the chance of these diseases being diagnosed at early stages," the commission said.

Robert Scherpbier, a heath official from United Nations Children's Fund, said that there has been a large increase in the incidence of thyroid cancer in most countries over the past 30 to 40 years.

"Rates of papillary thyroid cancer are increasing in countries with increasing, stable and decreasing iodine intake," he said. "There is greater evidence that iodine deficiency, instead of excess, causes thyroid disorders."

Improved diagnostic ability to detect small carcinomas is creating the illusion that thyroid disease is more prevalent than before, he said.

Thyroid cancer has been one of the most rapidly increasing cancers in many parts of China in the past two decades, according to the National Health and Family Planning Commission. This has caused worries among the public in recent years that the intake of iodine can cause the cancer, according to media reports.

In China, more than 90 percent of households consume iodized salt, and as a result iodine deficiency has been eliminated in children and pregnant women, according to a report by the National Health and Family Planning Commission, UNICEF and Global Alliance for Improved Nutrition completed in March.

In most areas of China, where iodine is lacking in the environment, the risk of iodine deficiency is greater than the risk of iodine excess and therefore it is critical to continue adding iodine to salt, the report said.

Before China began using iodized salt in 1994, 60 percent of Chinese were affected by iodine deficiency, which helped create 8 million goiter patients, according to official figures.

Dai Weixin, a professor in the endocrinology department of Peking Union Medical College Hospital, said most areas of China lack iodine, which makes consuming iodized salt the only way to make up for the deficiency.

"Even a slight excess of iodine intake will not cause harm to most people," he said.