Wetenschap - 30 augustus 2001

Sixteen million Chinese suffer from too much iodine in well water

Sixteen million Chinese suffer from too much iodine in well water

At first the Chinese authorities thought that the population in the province of Jiangsu was suffering from a shortage of iodine. Doctors reported many cases of goitre or an enlarged thyroid gland. Epidemiologist Jinkou Zhao was asked to research the matter, and turned it into a PhD.

Zhao quickly discovered that the problem was not caused by an iodine shortage: the people he examined had extraordinarily high concentrations of iodine in their urine. "The culprit is the drinking water," explains Zhao. "The region is dry, and drinking water comes from wells. The geology of the area is responsible for an abnormally high level of iodine in the water." Zhao calculated that a total of sixteen million Chinese get more iodine than is good for them.

An excess of iodine as a result of natural circumstances is fairly rare. The opposite, iodine deficiency, is far more common. Until governments started adding iodine to bread and salt, people in large areas of the world suffered from a lack of iodine. Most cases of people ending up with too much iodine in their bodies are due to overenthusiastic manufacturers who have added too much to their products.


Paradoxically, too much iodine leads to the same effects as a deficiency. The thyroid gland needs iodine to make the hormone thyroxine. If it receives too little, the gland becomes enlarged and starts producing less thyroxine. Symptoms of iodine deficiency include slower metabolism, a fall in body temperature, breakdown of muscle tissue and an increase in the amount of fat.

In children mental development slows down, they become listless and their IQ may go down. An overdose of iodine has the same effect, although the symptoms are usually not as severe. Zhao's research also confirmed this. The thyroid glands of school children in regions with abnormally high concentrations of iodine in the drinking water were on average 13 percent larger than normal. Their IQ was also three to four points lower.

"It was not difficult to reverse the results of an excess of iodine," says Zhao. "In the towns where the government reduced the amount of iodine to a normal level, the school children had a normally functioning thyroid within three months." Zhao's research gives the Chinese government the information it needs to solve the problem. "What we will have to do is to dig new wells to reach better quality water," comments Zhao.

Jinkou Zhao will defend his PhD on 4 September 2001. He was supervised by Professor of nutrition and health Jo Hautvast, and Professor Clive West, chair of Nutrition in relation to sickness and health at the University of Nijmegen and head of the Human Nutrition and Epidemiology Group at Wageningen University.

Willem Koert