Thyroid Cancer Risk Soy

In recent years, soy has almost reached the pop-culture healing status of chicken soup, and it’s reputed to reduce the risk of heart disease, prevent osteoporosis and ward off some forms of cancer. However, the relationship between the thyroid and soy remains complex.

Soy Products: Thyroid Links?

Medical researchers hold a wide range of opinions regarding the thyroid problems/soy products connection.

Soy products are thought to interfere with the body’s ability to absorb thyroid medication. At one end of the spectrum are those who claim that soy is merely one of the products that block medication absorption, similar to high-fiber foods, iron and calcium supplements. They recommend that patients taking thyroid hormone replacement medication do so on an empty stomach and wait four hours before eating any soy products.

However, since soy is found in so many foods — from chips to soymilk — thyroid patients should read nutrition labels carefully.

At the other end of the spectrum are researchers who maintain that a clear connection has been established between soy products and the risk of thyroid disease. A 2006 Czech study found that even small differences in soy phytoestrogen affect the thyroid, especially when the consumption of iodine is low. And a 2004 study found an increase in thyroid stimulating hormones among infants who’d been fed soy formula.

Soy Products, Goiters and Warnings

The strong link between soy products and goiters, abnormally enlarged thyroid glands, is undisputed. Some vegetables and grains, like soy, promote the growth of goiters, which may lead to thyroid disease.

The Israeli Health Ministry has suggested that parents avoid feeding infants soy products and limit soy consumption in young children. France’s Center for Cancer Research maintains that children under three and women with (or at high risk for) breast cancer should not eat soy products.

Soy Products/Thyroid Safety

Some researchers recommend that soy consumption be limited in order to prevent thyroid problems.

Americans may be getting much more than 30 mg of isoflavones a day. Some soy supplements have as much as 300 mg. Even without supplements, soy-enriched foods, soy candy bars, soy cereal and soy milk can provide 80 to 100 mg of soy isoflavones a day.


Nippoldt, T. (2010). Is it true that people who have hypothyroidism should avoid soy? Retrieved March 11, 2010, from the Mayo Clinic Web site:

Health Services At Columbia staff. (2003). What are the benefits of soy? Retrieved March 11, 2010, from the Go Ask Alice Web site: