Worried about a connection between soyfoods and thyroid cancer? Even snopes.com (the famous urban legend whistle-blower) found such a rumour circulated in a mass email circa 2003. We can’t find a good reason to be worried, however. Here’s what’s been discovered…
In her SOY AND THYROID REVIEW (August 2001), Clare M. Hasler, Ph. D, begins by saying, ” There is no convincing evidence that soy protein has an adverse effect on thyroid function in healthy humans consuming adequate iodine, particularly at the moderate level of soy protein consumption (25 grams) recommended due to the approval of a health claim for coronary heart disease.”
Of particular interest was the following statement:
“One of the concerns that has been expressed about high soy intake is an increase in thyroid cancer. A recent population-based case-control study examined the effect of phytoestrogen intake on the incidence of thyroid cancer (Horn-Ross et al, 2001) in women ages 20-74 (608 cases of thyroid cancer and 558 controls). Phytoestrogen consumption was assessed with a food frequency questionnaire which determined the intake of isoflavones, coumestans, and lignans, all of which were associated with a reduced risk of thyroid cancer, not an increase in thyroid cancer. The authors identified possible mechanisms associated with the reduced risk of thyroid cancer in this study as antioxidant effects, direct effects on endogenous estrogen and/or thyroid hormone levels, or anti-estrogenic effects resulting from competitive binding to the estrogen receptor.”
According to Dr. Tori Hudson, N.D., “the epidemiological data shows that consumption of nonfermented soy products, such as soymilk and tofu, tended to be either protective or not associated with cancer risk; however no consistent pattern was evident with the fermented soy products, such as miso. Protective effects were observed for both hormone and nonhormone related cancers.”
John Robbins points out, “in November, 2001, Pamela Horn-Ross from the Northern California Cancer Center announced the results from a study of soy intake and thyroid cancer risk. In the study, both total soy consumption and the intake of individual soyfoods were found to be protective against thyroid cancer. In contrast to what you have heard, it appears likely that soy consumption actually decreases the risk of thyroid cancer. This is consistent with the many studies that have found soy intake to lower the risk of breast cancer and prostate cancer.”
We also have information on soy & thyroid disease, if you’d like to read more.