Thyroid Cancer and Soy
April 18th, 2010

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Dear John,

I have been diagnosed with thyroid cancer, and have for many years eaten soy foods. I’ve been told that soy consumption increases the risk of thyroid cancer. Is this true? Could soy foods have caused my cancer? If not, what might have caused it? Am I going to die?

Thanks for your help,


Dear Susan,

I am sorry to hear of your cancer. Life sure can throw us some curve balls, can’t it? Then it’s up to us as to how we respond.

The bad news is that thyroid cancer requires treatment and lifelong monitoring, and can have some pretty difficult effects on patients. The good news is that survival rates are high, with 95% of all thyroid cancer patients in the United States achieving long-term survival without reoccurrence.

There are four main types of thyroid cancer: Papillary, Follicular, Medullary, and Anaplastic.

Papillary cancer is the most common type of cancer (60-70% of all cases), perhaps because papillaries are quite common in the thyroid gland. Papillary cancer mostly involves one side of the thyroid and sometimes spreads into the lymph nodes. The cure rate is very high.

Follicular cancer, the second most common type of thyroid cancer (10-15% of all cases), is somewhat more malignant than papillary. The thyroid gland is comprised of follicles which produce thyroid hormones that are essential for growth and development of all body tissues. This cancer doesn’t usually spread to the lymph nodes, but it may spread to arteries and veins of thyroid gland and more distantly (lung, bone, skin, etc), though that is uncommon. Follicular cancer is more common in older people. Again, the long -term survival rate is high.

Medullary thyroid cancer is much less common (2-8% of all cases), and usually originates in the upper central lobe of the thyroid. It spreads to the lymph nodes earlier than papillary or follicular cancers. It differs from papillary and follicular cancer, however, in that it does not arise from cells that produce thyroid hormone, but instead from C cells. These C cells make the hormone calcitonin. This type of cancer can run in families, and also has a good cure rate.

Anaplastic is the most serious thyroid cancer. It appears in 5-10% of all cases. It can spread early to lymph nodes, thus usually the cause for a visit to the doctor is a mass in the neck. It also is the form of thyroid cancer most likely to spread to other organs beyond the thyroid or lymph nodes. This type of thyroid cancer is more common in those over 65 and in men. Long-term survival rates are unfortunately far less than for the other three types of thyroid cancer.

Some animal studies have shown a link between soy intake and the development of goiter, but no such link has been found in human studies. (Goiter is the enlargement of the thyroid gland, causing swelling of the neck. The primary cause of goiter in humans is a deficiency of dietary iodine, which is necessary for the production of thyroid hormone. The gland enlarges in an attempt to increase the output of hormone.)

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. I would have to say it is very unlikely that you consumption of soy foods has had anything to do with the development of your cancer.

A more likely cause is exposure to radiation. Ionizing radiation causes changes in the genes of the thyroid cells, and is a widely recognized risk factor for thyroid cancer. People who received radiation to the head and neck area when they were young (under 30 years old) are at highest risk. This practice has been largely abandoned in medical circles (apart from cancer therapy) for this very reason, but it was formerly used as a treatment for a wide range of conditions, including many trivial ones. Japanese atomic bomb survivors have a much higher-than-normal rate of thyroid cancer, as do those exposed to fall-out from Chernobyl. Flight attendants and pilots also have increased rates. Slow growing thyroid cancers often take 10 – 30 years after the radiation exposure to become apparent.

Another established risk factor for thyroid cancer is higher weight. One study found that women who weigh more than 132 pounds have 2.5 times the rate of thyroid cancer compared to those weighing less than 114 pounds. On the dietary front, risk factors include diets deficient in selenium, and those either deficient in or providing too much iodine. Many studies have found a protective association for vegetables and fruits.

I do wish you all the best in your journey with cancer. I know how frightening it can be. The Dalai Lama has spoken about “turning adversity into one’s ally.” This is easier said than done, of course, but I do like to keep the concept in mind when dealing with difficult circumstances.

Are you going to die? I think we can be 100% certain that you will. Will it be as a result of your cancer? Probably not. But in the mean time, given that you and I and everyone we know will someday die, it might not be a bad idea to make the most of every precious second.

Be present,


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