China is a country with severe iodine deficiency, and most residents should consume iodized salt except in areas with high water iodine levels.
China has monitored and adjusted the iodine intake for many times, and the current iodine intake of residents is at an appropriate level, and eating iodized salt will not lead to iodine overdose.
Recently, some netizens said that the incidence of thyroid cancer has risen from the 15th to the 5th place among cancers, mainly due to the consumption of iodized salt, and that residents in coastal areas of China often eat seafood rich in iodine and do not need to eat iodized salt. Are these rumors true? People’s Daily interviewed the relevant departments and experts on this topic.
Question 1: Is iodized salt easy to induce thyroid cancer?
Response】 Thyroid cancer is related to genetic, autoimmune and mental factors; the benefits of iodine supplementation far outweigh the risks caused by excessive iodine.
“It is not accurate to say that the so-called increase of thyroid cancer is related to excessive iodine in salt.” Xiao Donglou, National Health Supervisor of the Department of Disease Control and Prevention, Ministry of Health, said, “Globally, most tumors, including thyroid cancer, have been on the rise in recent years. On the contrary, it is widely accepted that iodine supplementation can lead to a less malignant transformation of thyroid cancer.”
In response to the view that there is a high incidence of thyroid cancer, Wu Yijie, chief physician of the Department of Endocrinology and Metabolism of Shanghai First People’s Hospital, admits that the number of patients with thyroid disease is indeed increasing in clinical practice. “But this is not the same as an increase in the incidence of thyroid disease.” According to him, the medical examination means are more advanced than before, and the puncture technology can find tumors below 1 cm, while in the past, it could only be touched by hand.
“Iodine deficiency or iodine excess can lead to the development of thyroid disease.” Xiao Donglou said that excess iodine can increase the risk of hyperthyroidism and can also turn a latent thyroid autoimmune disease into a dominant one.
Can daily consumption of iodized salt bring about iodine overdose? Dai Weixin, professor of endocrinology at Peking Union Medical College Hospital, said, “Strictly speaking, the majority of people in China should consume iodized salt because the iodine in iodized salt is a trace amount, which is a basic amount. There is no relevant evidence that excessive consumption of iodized salt is directly related to thyroid disease.”
Wu Yijie said that, in general, the iodine intake of Chinese residents is at an appropriate level, but special circumstances in individual regions cannot be ruled out. Moreover, human thyroid hormone synthesis is a dynamic equilibrium, and occasional overdose will be excreted naturally and will not accumulate indefinitely in the body.
According to experts, the World Health Organization recommends a daily iodine intake of 150-300 micrograms for adults, and medical research institutions in the European Union and the United States consider the tolerable upper limit of iodine intake for adults to be 600 micrograms and 1100 micrograms per day, respectively. The average iodine content of iodized salt in China is 30 mg/kg. Based on a daily salt intake of 5-10 grams per person, the daily intake of iodine is about 150-300 micrograms. After deducting the loss from cooking and human metabolism, the iodine intake will not be higher than the WHO recommended amount.
Regarding the causes of thyroid cancer, Wu Yijie points out that it cannot be said that iodized salt leads to a high incidence of thyroid disease because the disease is related to genetic factors, autoimmune and mental factors, and people who work under stress and are in a long-term stressful situation also belong to the high incidence group.
In fact, experts believe that iodine deficiency is more dangerous than iodine overload. Chen Zupei, a professor at the Institute of Endocrinology of Tianjin Medical University, said, “The main role of iodine in the body is to synthesize thyroid hormones in the thyroid gland. Iodine deficiency can lead to insufficient synthesis of thyroid hormones, causing a series of symptoms and diseases, especially damage to intelligence. The average IQ of children in iodine deficiency areas is lower than normal, as shown by their IQ test examinations.”
“In addition to causing clinically typical iodine deficiency diseases such as endemic goiter, iodine deficiency also causes imperceptible intellectual impairment.” Xiao Donglou introduced the 2009 bulletin of the International Council for the Control of Iodine Deficiency Disorders, which concluded that the benefits of iodine supplementation far outweigh the relatively small risks caused by iodine overload.
Question 2: Do residents of coastal cities not need iodine supplementation?
[Response] Residents in coastal areas get 2.1% of their iodine from seaweed, nori and sea fish, and 84.2% of dietary iodine comes from iodized salt
“There are three ways for people to consume iodine: drinking water, food and air. Except for a part of China where the iodine content of drinking water is very high, the iodine content of most drinking water is relatively low, and the intake of iodine from air is even less.” Sun Dianjun, director of the Endemic Disease Control Center of the Chinese Center for Disease Control and Prevention, told reporters that “due to the influence of the external environment, the iodine content of food in China is also in the general form of iodine deficiency, so iodine supplementation is needed.”
In response to the netizen’s doubt that “the iodine content of seafood consumed by coastal residents is very high and iodized salt is not needed,” Chen Zupei explained, “In 2009, the results of a survey on the dietary iodine intake of residents in coastal areas conducted by the Ministry of Health in four provinces (cities), including Fujian, Shanghai, Zhejiang and Liaoning, showed that iodine-rich foods such as kelp, seaweed, sea fish, etc. are more abundant than iodine. The frequency and amount of iodine-rich foods such as seaweed, sea fish, etc. consumed by residents in coastal areas are very low. Without taking into account cooking losses, 84.2% of dietary iodine comes from iodized salt, and only 13.1% from various foods (including 2.1% from seaweed, nori and sea fish). If you consume non-iodized salt, more than 97% of the residents’ iodine intake will be lower than the recommended intake, and the risk of iodine deficiency is high.”
Sun Dianjun also believes that China is a country with severe iodine deficiency in the outer environment, not only in rural areas but also in cities. “In 2009, a survey on the dietary iodine intake of residents in coastal areas found that despite years of iodized salt supplementation, iodine nutrition for pregnant women in coastal cities such as Shanghai is still inadequate. That’s why big cities still need to supply iodized salt.”
“The results of “Risk Assessment of Salt Iodization and Residents’ Iodine Nutrition Status in China” released by the Ministry of Health in 2010 show that the iodine nutrition status of residents in the vast majority of areas in China is at an appropriate and safe level, except for areas with high water iodine, and coastal areas are no exception.” Xiao Donglou said.
Experts said that although residents of coastal cities need iodine supplementation, there are two kinds of people who should not eat iodized salt. One is the minority of people suffering from thyroid disease, who can follow medical advice not to consume or consume less iodized salt. The other is people who live in areas with high iodine levels, where iodine intake exceeds the recommended amount by several times.
According to the Shanghai CDC, high iodine areas are divided into water source and food source, and China was the first country to discover water source hyperiodized goiter. Currently, 130 counties in 12 provinces (regions and cities) in Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia, Jiangsu, Anhui, Fujian, Shandong, Henan, Shaanxi and Xinjiang are found to have excessive iodine levels in drinking water, with a threatened population of about 31 million people.
“In high iodine areas, people eat non-iodized salt instead of supplying iodized salt. For areas with high iodine in drinking water, they may even have to switch to a low iodine water source.” Sun Dianjun said.
Question 3: Is the standard for iodized salt “one size fits all”?
Response] The new standard implemented this year allows each province (district or city) to determine its own average level of iodine content in table salt.
There are also netizens who say that iodized salt standards should not be unified across the country and complain that it is difficult to buy non-iodized salt in the market. What is the actual situation?
In Beijing, the reporter visited several outlets designated by China National Salt Beijing to sell non-iodized salt, and found that there was sufficient non-iodized salt for sale, but only the 200-gram “Jingjing” organic non-iodized snowflake salt, priced at 4.5 RMB per bag, was available, with no restrictions on the quantity to be purchased and no medical prescription or certificate required. In addition to the designated supply outlets, the reporter also saw non-iodized salt at a Lotte Mart supermarket, where the salesman said “you can buy as much as you like”.
In Shanghai, the clerk at a Liangyou Golden Partner supermarket told reporters that the sale of non-iodized salt was normal and there was no rush or shortage. According to the Shanghai Municipal Health Bureau, Shanghai has been open to the sale of non-iodized salt since a long time ago, and currently there are 1,334 non-iodized salt supply points in the city.
It is understood that since 1995, when China began to implement a comprehensive salt iodization policy, the iodine content of salt has been adjusted several times. In this regard, Chen Zupei said that it is normal for China to monitor the iodized salt and the prevalence of iodine deficiency disease nationwide every 2 to 3 years and adjust the concentration of iodized salt according to the changes in the population.
The person in charge of the Shanghai CDC said that the iodine deficiency disease monitoring data shows that China is a vast country with large differences in salt intake, and the diet structure has changed in recent years, so the unified salt iodine content standard cannot meet and adapt to these changes. As a result, the Ministry of Health’s national food safety standard “Iodine Content of Edible Salt”, issued in September 2011 and implemented in March this year, allows each province (district or city) to determine its own average level of salt iodine content.
“In the past, the whole country was unified in one standard, which was the right thing to do in times of severe iodine deficiency and could quickly alleviate the nation’s iodine deficiency plight.” Chen Zupei added, “However, as the policy of salt iodization is gradually implemented, it will need to be gradually refined.” According to him, the appropriateness of iodine intake depends on many factors, including the concentration of iodized salt, the structure of food, and the amount of salt intake. For example, the daily salt intake per person in Shanghai, Tianjin and Beijing is about seven or eight grams, while the northern western region may have 12 or 13 grams, and the highest provinces to 20 grams. “The new standard leaves it up to each province to determine the concentration of iodine, reflecting the principle of ‘iodine supplementation according to local conditions and science’.”
It is understood that the iodine content in iodized salt varies from country to country around the world. Some countries in Western Europe use a salt iodine content of 10 mg-20 mg per kg, most countries in the Americas 50 mg-100 mg per kg, and the UK 25 mg per kg. China’s Iodine Content of Edible Salt stipulates that the average level of iodine content (in terms of elemental iodine) per kilogram of edible salt product is 20 mg-30 mg, and the allowable fluctuation range (uniformity) of iodine content of edible salt is ±30% of the average level of iodine content of edible salt.
“Iodized salt coverage in the United States is only 50-60%, but in addition to iodized salt, the United States increases iodine intake by adding iodine to milk; in Australia, iodine is added to bread.” Wu Yijie said, “The data shows that the per capita urinary iodine content in the U.S. is about 20% higher than in China.”