The campaign, which follows the nationwide promotion of iodine-fortified salt, is funded by the Global Alliance for Improved Nutrition (GAIN). Its goal is to raise public awareness of the need for proper nutrition.

Initiated on a trial basis in 2004, the campaign started with seven provinces, including Southwest China's Guizhou and East China's Jiangsu and Beijing, said Chen Junshi, the project's coordinator and a researcher with the Center for Disease Control and Prevention, which is carrying out the project.

The use of iron-fortified soy sauce has already helped reduce the incidence of IDA by 30 per cent in the seven trial provinces, Chen said.

However, the project still has a long way to go, Chen told China Daily.

"To date the general public still knows little about it, and only 50 million people, mainly in the seven pilot provinces, are using iron-fortified soy sauce," Chen said.

"However, iron deficiency is a problem for many more people."

It affects more than 20 percent of the public - impairing minds and bodies to the point where the condition has even had an effect on the country's economic performance, according to a survey about public nutrition.

Among rural women of childbearing age and children under 15, the IDA rate is above 40 percent.

An unbalanced diet lacking in regular servings of iron-rich foods like red meat, chicken and fish is mainly to blame for the problem, health experts said.

They also called for the campaign to be expanded.

"Extending the project so that it covered the entire population would have far-reaching significance in strengthening public health and strengthening the nation," Vice-Minister of Health Wang Longde said.

The project will take time to bear fruit, as success will be measured in improved public awareness of the need to use fortified products. This is different from the iodine-fortified salt campaign, which was mandatory, Chen said, calling on joint efforts between the government and producers of soy sauce.

At the moment, about 20 of the nearly 1,500 domestic soy sauce makers produce the fortified sauce - about 200,000 tons per year, said Wei Xiangtyun, the chair of an association of flavoring products.

Wei said annual domestic soy sauce output amounts to 5 million tons.

"To support the program, many of the 20 producers (making the fortified sauce) have said they will sell the iron-fortified soy sauce at the same price as the ordinary kind," Wei said, urging more producers to follow suit.