The national survey included nearly 53,000 Japanese women over 14 years. They looked at women aged 40 to 69 and found the group reported 134 thyroid cancer cases and 113 of those cases were papillary carcinoma.
Papillary carcinoma is a relatively common well-differentiated thyroid cancer. According to Medscape.com, these tumors may spread easily to other organs. The life expectancy of patients with this cancer is related to their age. The prognosis is better for younger patients than for patients who are older than 45 years.
According to the study, women who ate seaweed daily were 1.7 times more likely to develop cancer than those who ate it no more than twice a week.
The risk doubled among post-menopausal women, they were 3.8 times more likely to develop cancer than those who limited their intake.
Seaweed is a popular food in Japan. Not only because it is so plentiful but also because it is full of vitamins such as calcium, sodium, magnesium, potassium, iodine, iron and zinc. Seaweed is used for soup stock, seasonings and garnishes.
“Seaweed consumption was clearly associated with an increased risk of papillary carcinoma,” said the study led by the National Cancer Center and National Institute for Environmental Studies.
Iodine is essential for the body and is detected in every organ and tissue. It is found in high levels in the thyroid, breast, liver, lung, hear and adrenals. Iodine is also essential in pregnancy.
How much iodine someone needs everyday is controversial. Some claim the RDA is appropriate, which is about 150 mcg per day, while others claim more is needed. According to Medicinenet.com, the iodine intake in Japan may be as high as over 1000 micrograms a day.
It isn’t clear why post-menopausal women’s chances of getting thyroid cancer increased but they believe there is a link between the iodine found in seaweed, according to the research published in the European Journal of Cancer Prevention.
The survey did not say how much seaweed participants consumed during the study between 1993 and 2007.