May 15, 2024 is the 31st National Day for the Prevention and Treatment of Iodine Deficiency Diseases, and this year's theme is "Salt Iodization to Prevent Diseases, Balanced Nutrition and Health".
Iodine is an essential trace element in the human body, and the content in the human body is only 20~50 mg (an average of 30 mg). Although iodine is found in very low levels in the human body, it is an indispensable element for the development of various body systems, especially the nervous system.
Iodine is an important raw material for the synthesis of thyroid hormones by the human body. Thyroid hormones are involved in the body's metabolism and maintain the normal function of all organs. When iodine intake is stopped, the iodine reserves in the body are only enough to last for 2~3 months. The body's iodine is completely dependent on the supply of the natural environment, and once it is deficient, it will cause insufficient thyroid hormone synthesis in the body, resulting in hypothyroidism, and people are prone to fatigue, lack of concentration, and decreased work efficiency.
Who is susceptible to iodine deficiency
Pregnant women, lactating women, infants and young children aged 0~3 years, preschool and school-age children are the most vulnerable to iodine deficiency.
Pregnant and breastfeeding women Pregnant women have much higher iodine requirements than the average woman. In addition to meeting their own physiological needs, pregnant women should also supply iodine to the fetus to ensure that the needs of fetal growth and development are met. Iodine deficiency in the natural environment, pregnancy reactions of pregnant women, and salt avoidance will lead to insufficient iodine intake in pregnant women. As the fetus grows, the need for iodine increases in pregnant women. Once the pregnant woman does not consume enough iodine, it will lead to iodine deficiency in the fetus, resulting in brain development disorders, and after the birth of the child, the mild may become endemic subclinical cretinism, and the severe will become endemic cretinism.
Breastfeeding women are also sensitive to iodine deficiency because they need to supply both themselves and their infants and young children.
Infants and young children Infants and young children are in the second critical period of brain development and are as sensitive to iodine deficiency as their fetuses. Severe iodine deficiency in the fetus that persists into infancy develops into typical cretinism. If the degree of iodine deficiency in infants and young children is mild, they may become patients with subclinical cretinism or have only mild mental retardation, which is characterized by unresponsiveness to people and things around them, poor motor ability, and delayed mental and growth development. The iodine supply of infants and young children comes mainly from breast milk.
Children and adolescents Children and adolescents are in the period of growth and development, and their iodine requirements are significantly increased and they are more sensitive to iodine deficiency, which can cause damage to growth and development, including mental and physical development. Children in iodine-deficient areas do not develop intellectually at the level they should. Iodine deficiency in children during growth and development can lead to delayed or delayed physical development, short stature, skeletal muscle dysplasia or retardation, epiphyseal dysplasia or delayed closure, delayed or delayed sexual development, and decreased learning ability. The prominent manifestation of iodine deficiency in children and adolescents is goiter. Thyroid volume increases with age, and during adolescence due to increased iodine requirements, physiological goiter is predisposed. After a period of time after iodine supplementation, the enlarged thyroid gland can return to normal.
Can eating iodized salt prevent iodine deficiency disorders
Iodine supplementation is the fundamental measure to prevent iodine deficiency disorders. Iodine deficiency in the external environment (water, soil, etc.) in most parts of the continent, especially in mountainous areas, hilly areas, river valleys, desertification areas and river erosion areas, is more serious.
The body's ability to store iodine is limited, so iodine supplementation should follow the principles of long-term, micro, daily and convenient. People can't do without salt every day, and iodized salt supplementation is in line with the above principles. Practice has proved that salt iodization has the advantages of safety, effectiveness, simplicity, low price, and long-term persistence, and is the best way to supplement iodine.
Do seafood lovers still need to eat iodized salt?
Many people think that if they usually love kelp and seaweed, they don't need to eat iodized salt, but in fact, they don't.
The iodine content per 100 grams of dried kelp is 36,240 micrograms, the iodine content of dried seaweed is 4,323 micrograms per 100 grams, and the iodine content per 100 grams of fresh kelp is 2,950 micrograms. As a result, the iodine content of dried and fresh kelp varies greatly. In addition, the iodine content of different parts of kelp is also different, and the outer edge of the leaf contains more iodine, which is about twice that of the middle of the leaf. The content of organic iodine is higher in kelp near the roots, but in general, organic iodine accounts for only about 11% of kelp, that is, most of the kelp is inorganic iodine, and only a small part is organic iodine. There are also differences in iodine content in different regions, different sea areas, and different varieties of seafood.
In addition to seaweed products such as kelp and seaweed, fish, poultry, meat, egg products, pickled and animal foods, and seaweed foods, which are themselves iodine-rich foods, are relatively high in iodine. According to relevant surveys, the overall use rate of iodized salt in prepackaged foods is about 81.70%. The use rate of iodized salt in fermented foods was 87.50%, that of pickled foods was 88.89%, and that of other foods was 88.24%.
In addition, the iodine content of condiments is also different, some condiments have a higher iodine content, while others are relatively low, which is related to whether they contain iodized salt. Therefore, even regular consumption of seafood does not necessarily guarantee iodine intake.
The relationship between salt reduction and iodine supplementation
The Dietary Guidelines for Chinese Residents (2022) recommends that adults consume no more than 5 grams of salt per day. According to the national food safety standard "Iodine Content of Edible Salt" (GB 26878-2011), if the iodine content in edible salt is 25 mg/kg, the cooking loss rate is calculated according to the WHO recommended 20%, and 100 micrograms of iodine can be ingested from iodized salt per day. The vast majority of the mainland is an iodine-deficient area, the general population obtains about 10 micrograms of iodine from drinking water every day, and the daily iodine intake from food is 25~50 micrograms, so the total daily iodine intake of the general population can reach 135~160 micrograms. Thus, children and adults who consume iodized table salt can still reach the recommended iodine intake per day, even under reduced salt conditions, while pregnant and lactating women are at risk of iodine deficiency.
In conclusion, pregnant and breastfeeding women are advised to choose iodized salt with high iodine content while reducing salt, and encourage the intake of iodine-rich foods such as seafood, eggs, milk, etc.
Text: Liu Peng, Institute of Iodine Deficiency Disease Prevention and Control, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention
Finishing: Health News special reporter Yi Xiaofeng
Editor: Liu Yang Guan Zhongyao
Proofreading: Ma Yang
Review: Qin Mingrui, Xu Bingnan
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