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Please note: All of the physicians on this site are in agreement that low thyroid is under-diagnosed. This article by Michael Gerber, MD, HMD is a reprint from Healthy Beginnings Magazine.

Besides the great difficulty in diagnosing low thyroid function (hypothyroidism), because blood tests are notoriously inaccurate, as mentioned in Part 1 of 2 on this topic, there are hundreds – possibly thousands – of environmental toxins and genetic insults which block normal thyroid hormone levels at the cellular level. In this article, I will review a few of these hormone blockers.

Every White Blood Cell Needs Thyroid to Kill Bacteria and Viruses
All white blood cells, which kill bacteria, need thyroid to generate iodine. Bacteria are eaten by white blood cells that kill bacteria, viruses, and fungi by releasing peroxide and iodine from thyroid hormones. Chronic infectious conditions benefit from thyroid supplementation.

Thyroid Hormone Action is Disrupted by Bisphenol A
Thyroid disruptors have emerged as a major public health issue.  Bisphenol A (BPA) is a plastic that is widely used in daily life. It is in our drinking water, plastic water bottles, canned goods, and even in milk bottles. Many reports show that BPA contaminates, not only human plasma, but also fetal tissues. BPA can disturb thyroid hormone function by reducing T3 (the active thyroid hormone) binding to the nuclear thyroid receptors. The chemical structures of BPA and T3 are remarkably similar.

Fluoride, Bromide, Chlorine, and Perchlorate block Iodine Absorption by the Thyroid
There is a large amount of data to indicate that these substances block thyroid function. Fluoride in toothpaste, dental treatments, and in the water supply blocks iodine absorption in the thyroid. Bromide in baking oils, and chlorine as an antiseptic in water treatment, along with rocket fuel – especially in some 43 locales nationwide – also block thyroid function.

Mercury Exposure Linked to Increase Thyroid Antibody
Women with high mercury exposure are more than twice as likely to have higher levels of antibodies that are associated with autoimmune disorders. Patients with autoimmune disease such as lupus, rheumatoid arthritis and fibromyalgia, often have elevated concentrations of these antibodies. Studies found that women with the highest blood mercury levels were more than twice as likely to have elevated levels of antibodies against the thyroid.

Thyroid Enlargers (Goiters) in Foods
There are two general categories of foods that have been associated with disrupting thyroid hormone production in humans: soybean-related foods and cruciferous vegetables. In addition, there are a few other foods not included in these categories, such as peaches, strawberries, peanuts, radishes, spinach and millet that also contain goitrogens.

Isoflavones, such as genistein in soy products, block thyroid hormone by blocking an enzyme responsible for adding iodine to the thyroid hormone. A second category of foods associated with low thyroid production is the cruciferous food family. “Crucifers, including broccoli, cauliflower, Brussel sprouts, cabbage, mustard, rutabagas, kohlrabi, kale, and turnips contain isothiocyanates, which also reduce thyroid hormone formation.  Heating and cooking of these vegetables helps to inactivate the goitrogenic isothiocyanates.

Having Babies Can Cause Thyroid Problems
After delivering babies, thyroid inflammation is common in the mother within the first year after delivery.  Sometimes women develop overactive thyroid symptoms, and they are more likely to develop low thyroid symptoms, such as fatigue, depression, poor memory, feeling cold, constipation, muscle cramps and difficulty losing weight. Approximately 25% to 50% of women may have permanent hypothyroidism after babies.

Wheat Eating and Hypothyroidism
Gluten – wheat protein – has been linked to low thyroid disease. The structure of gluten/gliadin is similar to thyroid tissues and can cause cross-reactive destruction of the thyroid. The gluten free diet is important for some patients with low thyroid conditions.

Drugs That Cause Low Thyroid Function
Many drugs cause thyroid challenges. Steroids, beta blockers, amiodarone, salicylates (aspirin), some diuretics, IV heparin, phenytoin, metoprolol, lithium, interferon and SSRIs (antidepressants) are thyroid blockers.  This is a much abbreviated list.

A Few Other Issues
Aging and cognition are related to normal thyroid functioning. Even thyroid hormones and TSH levels within low-normal range appear to influence cognitive performance, such that low-normal thyroid function appears associated with cognitive decline over time.

Selenium, iodine and iron deficiency aggravate low thyroid conditions. Pesticide exposure causes increased risk of thyroid problems when exposed to aldrin, chlordane, DDT and lindane, fungicides such as benomyl, captan, maneb and the fumigants – methyl bromide –  are associated with significantly higher rates of thyroid problems.

In conclusion, thyroid deficiency, in my opinion, is rampant not only in women, but men, and not infrequently in children. Thyroid support and thyroid supportive lifestyle changes can reverse a host of symptoms and needs to be considered as a first line of defense for our health.

As it is impossible to avoid all thyroid toxins, remember to rotate your diet and cook your crucifers. A simple home test for low thyroid is to check your under arm temperature first thing in the morning for about 5 minutes for several days. Normal under arm (axillary) temperature should be 98 +/-.2. If the temperature is below 97.4 it may mean you are low thyroid. Some people run very low in the 94’s and 95’s. Blood testing every year or two with your doctor – especially the free T3 test – may be helpful to see if you are low or borderline low thyroid. As we mentioned in Part 1 of 2, testing can be misleading. So, if you have low thyroid symptoms – cold, dry, hair falling, weight gain, heavy periods, depression, fatigue, fibromyalgia, etc. – consider a trial of natural thyroid.


1. Kanji Moriyama, et al. Thyroid Hormone Action is Disrupted by Bisphenol A as an Antagonist. The Journal of Clinical Endocrinology & Metabolism November 1, 2002 vol. 87 no. 11 5185-5190
2. Mainardi E et al. Thyroid-related autoantibodies and celiac disease: a role of a gluten-free diet? J. Clinical Gastroenterology. 2002 Sept, 35(3):  245-8.