By David Liu, PHD

Wednesday April 11, 2012 (foodconsumer.org) -- A Japanese study released Wednesday suggests regular seaweed consumption by post-menopausal women heightened their risk of developing thyroid cancer, which is linked to iodine in an often claimed to be healthy food exactly because of iodine in it.

The association was derived from the 14-year national survey of about 53,000 Japanese women, aged 40 to 69, of whom 134 thyroid cancer cases were reported, including 113 cases of papillary carcinoma, a common thyroid cancer.

Researchers reported in the European Journal of Cancer Prevention those who ate seaweed daily were 1.7 times more likely to be diagnosed with thyroid cancer than those who ate it no more than twice a week, the study said.

The risk among post-menopausal women were about 3.8 times more likely to develop the cancer compared to those whose consumption of seaweed was limited.

Seaweed is a popular food in Japan. And ironically the Japanese lifespan is a few years longer than that of Americans who do not eat seaweed as often.

"Seaweed consumption was clearly associated with an increased risk of papillary carcinoma," reported the study led by the National Cancer Center and National Institute for Environmental Studies.

The association does not mean the increase in the risk of thyroid cancer is caused by eating seaweed while the possibility cannot be excluded either.  But if the increase in the risk has something to do with eating seaweed, then it must involve radioactive iodine in seaweed, the study report suggests.

Japanese women were at higher risk given that they eat seaweed more often, which can account for up to 80 percent of their iodine intake.

Early studies have shown high intake of iodine from seaweed can impair thyroid function.

The thyroid gland is located in the neck, below the thyroid cartilage.  It controls how the body uses energy and produces some important hormones. Thyroid dysfunctions or disorders can lead to a series of severe health consequences.