Results from the latest epidemiology study have pointed to a thyroid-related disease outbreak in China that may be related to the nation's 1995 mandate to add iodine to salt, experts said.

Roughly one out of 15 Chinese is suffering from hypothyroidism, one of the most commonly seen thyroid problems here, showed the study sponsored by the Chinese Medical Association's endocrinology branch. That's almost twice the incidence reported in late 1990s.

The survey, which started last March, sampled more than 15,000 people in 10 Chinese cities including Beijing, Guangzhou, and Shanghai in 17 months.

"The rising trend of thyroid problems is evidently seen on the mainland in recent years, but solid evidence of a link between iodized salt and the surge in thyroid ailments has yet to be confirmed," said Teng Weiping, who heads the endocrine research institute of the China Medical University based in Shenyang, Liaoning province.

Earlier reports said that too much iodine over a long period leads to rising hyperthyroid-related diseases.

Iodine intake is not the-more-the-better, Teng said. Iodine deficiency is widely known to cause thyroid problems, but excessive intake leads to problems as well.

The study also found that the prevalence of nodular goiter had increased to nearly 19 percent on the mainland, which was 10 percent in the 1990s.

Each year, the nation has at least 50 million cases of thyroid-related problems and a great majority remain undiagnosed, he said.

Notably, the awareness of these problems remains low among the general public, as a majority of the sufferers are not diagnosed, Teng said.

He urged the public, particularly women, to keep on high alert for hypothyroidism, which is caused by insufficient production of thyroid hormones by the thyroid gland. The disease usually leads to symptoms like poor muscle tone, fatigue, cold intolerance, increased sensitivity to cold, and constipation.

Women are at higher risk of developing hypothyroidism, experts said.

One in six women has the problem, Teng said, quoting the study.

The disease can cause infertility because it can prevent the production of eggs.

Also, a pregnant woman with hypothyroidism faces a higher risk for miscarriage.

Left untreated, babies born to such mothers may not achieve their full intellectual potential, he added.

To address that, experts called for universal screening on thyroid-related diseases primarily among pregnant women in China.