A recent study conducted by researchers from Severance Hospital suggested that consuming seaweed more than five times a week might be associated with a reduced risk of thyroid cancer.

The research, conducted by a team of professors from various departments at Severance Hospital, Yonsei Cancer Center, and Gangnam Severance Hospital, found a 58 percent lower prevalence of thyroid cancer among individuals who frequently consumed seaweed compared to those who ate it less than once a week.

According to the 2021 Cancer Registration Statistics, thyroid cancer has been the most commonly diagnosed cancer in Korea for three consecutive years, with an incidence rate of 68.6 per 100,000 people.

Despite iodine being linked to an increased risk of papillary thyroid cancer, which is prevalent in Korea, this study provides new insights into the effects of iodine-rich foods on thyroid cancer incidence.

The research team, led by Professors Lee Ji-won and of the Department of Family Medicine at Severance Hospital, Kang Sang-wook of the Department of Surgery at Yonsei Cancer Center, Kwon Yu-jin of the Department of Family Medicine at Yongin Severance Hospital, and Lee Hye-sun of the Department of Research Affairs at Gangnam Severance Hospital, utilized data from the Korean Genome and Epidemiology Study (KoGES), analyzing dietary habits of 169,057 thyroid cancer patients.

They identified eggs, seaweed, and dairy products as the top three iodine-rich foods frequently consumed by the participants. The recommended daily intake of iodine varies by age and sex, with the general adult recommendation being 150 micrograms, increasing to 240 micrograms for pregnant women and 340 micrograms for breastfeeding women.

Participants were categorized based on their consumption frequency of these foods -- more than five times a week, three to four times a week, one to two times a week, and less than once a week.

The analysis revealed a significant inverse correlation between seaweed consumption and thyroid cancer prevalence.

Those consuming seaweed more than five times a week had a 58 percent lower prevalence compared to the less than once a week group. Similarly, the three to four times a week and one to two times a week groups had a 43 percent and 32 percent lower prevalence, respectively.

Dairy product consumption also showed a potential protective effect, with the three to four times a week group having a 24 percent lower prevalence compared to the less-than-once-a-week group. However, no significant correlation was found between egg consumption frequency and thyroid cancer prevalence.

"While high iodine intake is associated with an increased risk of papillary thyroid cancer in Korea, this study suggests that the type of iodine-containing food is a critical factor," Professor Lee Ji-won said. "Excessive iodine intake is harmful, but avoiding iodine-rich foods altogether is not necessary. Moderate consumption of seaweed could help prevent thyroid cancer."

The study results were published in Nutrients.