Sushi has been linked to thyroid illness.Sushi has been linked to thyroid illness.
SUSHI lovers beware - eating too much of the popular Japanese dish can cause serious health problems.

Consuming more than a handful of the seaweed used as a wrap for sushi rolls or in soups and stews each week can affect the thyroid gland.

Dietitians Association of Australia's Lisa Renn said sushi was a healthy meal but only if restricted to two or three rolls twice a week because of the iodine levels in the seaweed wrap.

Illustration: Matt Golding
Last month, a type of dried seaweed sold in Asian food supermarkets was recalled after it was found to have high levels of iodine, which is particularly dangerous for pregnant women.

Food Standards Australia New Zealand ordered the recall of the Korean-packaged Wang Dried Kelp Varech Speche.

In a separate case, Heng Fai Trading Co Pty Ltd voluntarily recalled its Dried Seaweed product last year because of unusually high iodine levels.

''When we talk about a healthy diet, variety is the key so I would not recommend having sushi every day,'' Ms Renn said.

According to the Food Standards Australia New Zealand, one sushi roll contains 92 micrograms (one millionth of a gram) of iodine. The recommended daily intake of iodine for adults is 150 micrograms (20,000th of a teaspoon).

The thyroid, a small butterfly-shaped gland in the lower part of the neck, needs iodine to produce essential hormones that regulate the metabolism. But excessive amounts of iodine can lead to hyperthyroidism (overactive thyroid causing symptoms including palpitations, fatigue and weight loss) while low levels can cause hypothyroidism (underactive thyroid causing fatigue, weight gain and confusion).

Thyroid Australia estimates about 850,000 Australians suffer from thyroid dysfunction, with more than 40,000 new cases developing each year.

The Federal Department of Health and Ageing, alarmed by the increasing number of people with thyroid conditions linked to seaweed, issued a warning to doctors, endocrinologists and state and territory chief health officers last year.

Victoria's Department of Human Services, the National Health and Medical Research Council and Food Standards Australia New Zealand told The Sunday Age they agreed with Ms Renn that eating too much sushi could be a health risk.

DHS spokesman Graeme Walker said that since October, dried brown seaweed with iodine levels above 1000 milligrams per kilogram had been banned for importation into Australia following the Bonsoy case.

In December 2009, Bonsoy soy milk, which was made using kombu seaweed extract, was forced to launch a worldwide recall after people fell ill due to its high iodine levels. It was reformulated without the kombu seaweed extract and is back on the market.

Pregnant and breastfeeding women and children are particularly at risk if they eat more than one serve a week of brown seaweed because of its high iodine content.

Brown seaweed, such as kelp, kombu, wakame, quandai-cai, hijiki, arame or Sargassum fusiforme, is usually sold dried for use in soups and stews. Confusingly, these seaweeds can be green, black or brown.

Nori and other red and green seaweed used in dishes such as sushi and miso soup are considered safer than brown seaweed.