Soy may exacerbate hypothyroidism
It seems like everyone has heard of hypothyroidism. But do we really know what it is and why it is important? The thyroid is a butterfly-shaped organ responsible for maintaining our metabolism. It sits at the base of the neck, just below the laryngeal prominence or Adam’s apple. The prefix “hypo,” derived from Greek, means “under” (1). Therefore, hypothyroidism indicates an underactive thyroid and results in slowing of the metabolism. Many people get hypo- and hyperthyroidism confused, but they are complete opposites.
Blood tests determine if a person has hypothyroidism; they include thyroid stimulating hormone, which is usually increased, thyroxine (free T4), and triiodothyronine (free T3 or T3 uptake), which may both be suppressed (2).
There are two types of primary hypothyroidism: subclinical and overt. In the overt (more obvious) type, classic symptoms include weight gain, fatigue, thinning hair, cold intolerance, dry skin, and depression, as well as the changes in all three thyroid hormones on blood tests mentioned above. In the subclinical, there are may be less obvious or vague symptoms and only changes in the TSH. The subclinical can progress to the overt stage rapidly in some cases (3). Subclinical is substantially more common than overt; its prevalence may be as high as 10 percent of the U.S. population (4).
What are potential causes or risk factors for hypothyroidism? There numerous factors, such as medications, including lithium; autoimmune diseases, whether personal or in the family history; pregnancy, though it tends to be transient; and treatments for hyperthyroidism (overactive thyroid), including surgery and radiation.
The most common type of hypothyroidism is Hashimoto’s thyroiditis (5). This is where antibodies attack thyroid gland tissues. Several blood tests are useful to determine if a patient has Hashimoto’s: thyroid peroxidase antibodies and antithyroglobulin antibodies.
I would like to separate the myths from the realities with hypothyroidism. Does treating hypothyroidism help with weight loss? Not necessarily. Is soy potentially bad for the thyroid? Yes. Does coffee affect thyroid medication? Maybe. Does subclinical hypothyroidism negatively impact cholesterol? There are studies that suggest this. And finally, do vegetables, specifically cruciferous vegetables, negatively impact the thyroid? Probably not. Let’s look at the evidence.
Treatments: medications and supplements
When it comes to hypothyroidism, there are two main medications: levothyroxine and Armour Thyroid. The difference is that Armour Thyroid converts T4 into T3, while levothyroxine does not. Therefore, one medication may be more appropriate than the other, depending on the circumstance. However, T3 can be given with levothyroxine, which is similar to using Armour Thyroid.
What about supplements? A recent study tested 10 different thyroid support supplements; the results were downright disappointing, if not a bit scary (6). Of the supplements tested, 90 percent contained actual medication, some to levels higher than what are found in prescription medications. This means that the supplements could cause toxic effects on the thyroid, called thyrotoxicosis. Supplements are not FDA-regulated, therefore they are not held to the same standards as medications. There is a narrow therapeutic window when it comes to the appropriate medication dosage for treating hypothyroidism, and it is sensitive. Therefore, if you are going to consider using supplements, check with your doctor and tread very lightly.
What role does soy play with the thyroid? In a randomized controlled trial, the gold standard of studies, the treatment group that received higher amounts of soy supplementation had a threefold greater risk of conversion from subclinical hypothyroidism to overt hypothyroidism than those who received considerably less supplementation (7). Thus, it seems that in this small yet well-designed study, soy has a negative impact on the thyroid. Therefore, those with hypothyroidism may want to minimize or avoid soy. Interestingly, those who received more soy supplementation did see improvements in blood pressure and inflammation and a reduction in insulin resistance but, ultimately, a negative impact on the thyroid.
The reason that soy may have this negative impact was illustrated in study involving rat thyrocytes (thyroid cells) (8). Researchers found that soy isoflavones, especially genistein, which are usually beneficial, may contribute to autoimmune thyroid disease, such as Hashimoto’s thyroiditis. They also found that soy may inhibit the absorption of iodide in the thyroid.
Since being overweight and obese is a growing epidemic, wouldn’t it be nice if the silver lining of hypothyroidism is that, with medication to treat the disease, we were guaranteed to lose weight? In a recent retrospective (looking in the past) study, results showed that only about half of those treated with medication for hypothyroidism lost weight (9). This has to be disappointing to patients. However, this was a small study, and we need a large randomized controlled trial to test it further.
WARNING: The FDA has a black box warning on thyroid medications — they should never be used as weight loss drugs (FDA.gov). They could put a patients in a hyperthyroid state and worse, have potentially catastrophic results.
I am not allowed to take away my wife’s coffee; she draws the line here with lifestyle modifications. So I don’t even attempt to with my patients, since coffee may have some beneficial effects. But when it comes to hypothyroidism, taking levothyroxine and coffee together may decrease the absorption of levothyroxine significantly (10). It did not seem to matter whether they were taken together or an hour apart. This was a very small study involving only eight patients. Still, I recommend avoiding coffee for several hours after taking the medication. This should be okay, since the medication must be taken on an empty stomach.
There is a theory that vegetables, specifically cruciferous ones, may exacerbate hypothyroidism. In one animal study, results suggested that very high intake of these vegetables does reduce thyroid functioning (11). This study was done over 30 years ago, and it has not been had replicated.
Importantly, this may not be the case in humans. In the recently published Adventist Health Study-2, results showed that those who had a vegan-based diet were less likely to develop hypothyroidism than those who ate an omnivore diet (12). And those who added lactose and eggs to the vegan diet also had a small increased risk of developing hypothyroidism. However, this trial did not focus on raw cruciferous vegetables, which is much needed.
There are two take-home points: try to avoid soy products and don’t think that supplements that claim to be thyroid support are good for you or harmless because they are over the counter and “natural.” In my experience, an anti-inflammatory diet helps improve quality of life issues, especially fatigue and weight, for those with Hashimoto’s thyroiditis.
(1) dictionary.com. (2) nlm.nih.gov. (3) Endocr Pract. 2005;11:115-119. (4) Arch Intern Med. 2000;160:526-534. (5) mayoclinic.org. (6) Thyroid. 2013;23:1233-1237. (7) J Clin Endocrinol Metab. 2011 May;96:1442-1449. (8) Exp Biol Med (Maywood). 2013;238:623-630. (9) American Thyroid Association. 2013;Abstract 185. (10) Thyroid. 2008;18:293-301. (11) Crit Rev Food Sci Nutr. 1983;18:123-201. (12) Nutrients. 2013 Nov. 20;5:4642-4652.
Dr. Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management. For further information, go to the website medicalcompassmd.com and/or consult your personal physician.