Thyroid/Breast Cancer Connection!
I’m a fan of aggressive prevention, and what better diagnosis to prevent than cancer? Many of my patients don’t realize that the hormonal balancing and nutraceutical prescriptions we co-create in my integrative medical practice are often in the service of cancer risk reduction. More specifically, many of my patients don’t realize the crucial link between healthy boobs and their thyroid. Who knew?
I do not mean to be glib about the diagnosis of breast cancer. I personally have a positive family history and know first-hand the deeply emotional and complicated issues reflected in this diagnosis. But what troubles me is the tremendous distortion I’ve seen in the media’s oversimplification of how hormones “cause” breast cancer. The truth is far more nuanced and worth digesting.
It is not surprising to find a link between thyroid troubles and breast cancer. Look at the epidemiology – both conditions share a predominance in women, with a peak incidence in menopause. What else do the breast and thyroid have in common? Both tissues take up and use dietary iodine. Research has shown that iodine or iodine-rich seaweed inhibits breast tumor growth, and is further supported by the outrageously low rates of breast cancer in Japanese women living in Japan and eating a traditional Japanese diet (for more data on this, see Daphne Miller’s new book, The Jungle Effect). When Japanese women move to the U.S. and consume a standard American diet (SAD), their breast cancer rates approach the epidemic levels that we have here in the States.
Let’s address specifically the role of thyroid optimization and risk of cancer generally, and, specifically, breast cancer. Here’s what we know:
- Women with breast cancer are 2 times more likely to have thyroid antibodies than women without breast cancer
- Pre-menopausal women with thyroid cancer are at increased risk for breast cancer 5-20 years later according to MD Anderson Cancer Center. Breast cancer is not associated with an increased risk of thyroid cancer, which suggests that thyroid cancer treatment with post-surgical radio-active iodine (RAI) was the reason for the greater risk.
- Non-toxic goiter (an enlarged thyroid) is twice as common in women with breast cancer
- Survival from breast cancer is improved if your TSH is normal (i.e., your are “euthyroid”). In women with breast cancer with underactive thyroids, survival from breast cancer was 0% at 16 months, and in euthyroid survivors, survival at 16 months was 100% (older data – Journal of the American Medical Association, 1963)
- Thyroid problems that are benign (non-malignant, such as Graves, Hashimoto’s thyroiditis) correlate with risk of cancer (bladder, kidney, blood, and thyroid cancer), particularly in women with low free T3 and normal TSH (Thyroid, 1998).
Unfortunately, there is no clear consensus about how thyroid hormone may influence breast tissue. In fact, there are additional studies showing conflicting results, such as a 2005 study, also from M.D. Anderson, showing reduced risk of breast cancer in hypothyroid patients.
Most research to date has focused on the role of sex hormones (estrogen, progesterone, testosterone) on breast tissue, but thyroid hormone shares similar mechanisms in control of cell growth and proliferation.
What about iodine? Before you start munching on kelp, a few words. Many of us here in the US are iodine deficient, and this was addressed here in the States and in other industrialized countries by adding iodine to salt several decades ago. Yet 45% of households don’t use iodized salt. Now we are starting to see areas of iodine deficiency again. However, both slightly too much and slightly too little iodine can be a problem for you. Excess iodine in some of us thyroid-sensitive folk can worsen autoimmune thyroiditis. Overall, in the US we consume an average of 240 micrograms of iodine per day, and 15% of women in the US are moderately to severely iodine deficient. In Japan, the average consumption is 12 mg of iodine, a 50-fold greater amount. Why don’t the Japanese have a problem with consuming too much iodine? Does it protect them from breast cancer? Do they have a higher rate of thyroid problems? No – their rates of thyroid dysfunction are similar to ours.
What to do? Regarding iodine, best bet is to test your iodine and see how much you need individually. Many of us take a multivitamin with 100-200mcg of iodine, and that is probably a safe amount, but may be excessive if you also consume a lot of shellfish and/or sea vegetables. I favor testing – moderate to severe deficiency is defined as urine excretion of iodine of less than 50 mcg/L.
Regarding breast cancer risk and thyroid dysfunction, I believe the safest route given the findings is the voice of reason: seek euthyroidism (in my book, that’s a TSH of 0.35-2.0 with an absence of thyroid symptoms) combined with evidence-based breast cancer screening. I agree with the new mammogram guidelines: perform first baseline at age 50, and perform mammogram (preferably digital – less radiation) every 2 years after that. Some of my patients favor thermograms in their 40s and alternated with their mammo in their 50s+.
For my friends with greater concern, a family history of breast cancer, or a personal history of thyroid cancer followed by RAI, or just want to be aggressively preventive, another great option is to check your 2/16 ratio of estrogen metabolism. High levels of 4-hydroxy-quinone estrogen and 16-alpha-hydroxy-estrone correlates with greater risk of breast cancer. Many labs offer this test, one of my favorites is offered by Genova. Other important lifestyle factors that reduce breast cancer risk are staying lean (Body Mass Index 19-25), limiting alcohol (less than 4 x 4oz servings of wine or beer per week), and more cruciferous vegetables (brussel sprouts, broccoli and the like).
Written by, Sara Gottfried, MD
Tags: cancer overview, dietary iodine, enlarged thyroid, hormones causing breast cancer isn't a fact necesssarily, iodone, link between breast cancer and thyroid cancer, menopause and thyroid, non-toxic goiter, RAI thyroid and breast cancer, sex hormones, thyroid breast cancer connection, thyroid optimization, written by Sara Gottfried MD