Thyroid hormone replacement has been used for more than a century to treat hypothyroidism. Natural thyroid preparations (thyroid extract, desiccated thyroid, or thyroglobulin), which contain both thyroxine (T4) and triiodothyronine (T3), were the first pharmacologic treatments available and dominated the market for the better part of the 20th century. Dosages were adjusted to resolve symptoms and to normalize the basal metabolic rate and/or serum protein-bound iodine level, but thyrotoxic adverse effects were not uncommon. Two major developments in the 1970s led to a transition in clinical practice: 1) The development of the serum thyroid-stimulating hormone (TSH) radioimmunoassay led to the discovery that many patients were overtreated, resulting in a dramatic reduction in thyroid hormone replacement dosage, and 2) the identification of peripheral deiodinase-mediated T4-to-T3 conversion provided a physiologic means to justify l-thyroxine monotherapy, obviating concerns about inconsistencies with desiccated thyroid. Thereafter, l-thyroxine mono-therapy at doses to normalize the serum TSH became the standard of care. Since then, a subgroup of thyroid hormone–treated patients with residual symptoms of hypothyroidism despite normalization of the serum TSH has been identified. This has brought into question the inability of l-thyroxine monotherapy to universally normalize serum T3 levels. New research suggests mechanisms for the inadequacies of l-thyroxine monotherapy and highlights the possible role for personalized medicine based on deiodinase polymorphisms. Understanding the historical events that affected clinical practice trends provides invaluable insight into formulation of an approach to help all patients achieve clinical and biochemical euthyroidism.
From the early 1890s through the mid-1970s, desiccated thyroid was the preferred form of therapy for hypothyroidism (Appendix Table, available at www.annals.org). This preference was reinforced by the unique ability of desiccated thyroid to reproduce a normal serum PBI (33). The predominance of natural thyroid products was illustrated by prescribing patterns in the United States: In 1965, approximately 4 of every 5 prescriptions for thyroid hormone were for natural thyroid preparations (38). Concerns about inconsistencies in the potency of these tablets arose (26) after the discovery that some contained anywhere from double to no detectable metabolic activity (39). The shelf-life of desiccated tablets was limited, especially if the tablets were kept in humid conditions (36). There were reports of patients not responding to desiccated thyroid altogether because their tablets contained no active thyroid hormone. It was not until 1985 that the revision of the U.S. Pharmacopeia standard from iodine content to T3/thyroxine (T4) content resulted in stable potency (38), but by then the reputation of natural thyroid products was tarnished (40).
The thyroid uses iodine to convert T4 into freeT3. If you have hypothyroidism, you may not have an iodine deficiency per se, but your thyroid is almost certainly struggling in some way to get ahold of the iodine available to it and do what it needs to do with it. If the root cause is left unaddressed, simply increasing iodine is not always useful and at worst can be dangerous depending on how high you’re increasing your supplementation thinking if a little is good, then more will “solve” your problem.
You may find that changing your diet will help. One suggestion is to reduce or eliminate sugar, limit fruit, dairy, and grains, and get your carbohydrates mainly from vegetables. Round out your diet with lean proteins and healthy fats. In addition, eating two to three meals a day, no snacks, and avoiding food after 8 p.m. seems to help balance hunger hormones and blood sugar—and promote fat burning.
The amount in broccoli, cabbage, and kale in a usual diet is considered of minimal risk. For example, there was no adverse effect on thyroid function from consuming five ounces of cooked Brussels sprouts every day for four weeks.5,6 One note of caution, if you have a thyroid disorder, it's important to realize that juicing concentrates the amount of thiocyanate, on the order of 2000 mcg per glass.7
The normal values for the serum T4:T3 ratio are seldom discussed in the literature because measurement of serum T3 levels is not a recommended outcome in hypothyroidism (1). In a large study of approximately 3800 healthy individuals (4), the serum free T4:free T3 ratio was around 3, as opposed to a ratio of 4 in more than 1800 patients who had undergone thyroidectomy and were receiving l-thyroxine monotherapy. The corresponding serum free T4:free T3 ratio in patients continuing to receive desiccated thyroid is not well-defined, but the serum total T4:T3 ratio is known to be low (28, 50). In one study, the serum total T4:total T3 was about 40 in patients receiving desiccated thyroid and about 100 in those taking l-thyroxine monotherapy (60). Of course, this is affected by the timing of blood collection in relation to the timing of l-triiodothyronine administration, which is not commonly reported. Other key factors are the well-known poor reproducibility of the serum total T3 assay (61) and the interferences with direct measurement of free T3 (5).
The majority of people who have an underactive thyroid such as Hashimoto’s disease, have an autoimmune disease whereby the immune system attacks thyroid tissue. So, in order to find an underactive thyroid natural treatment it is important to address the autoimmune issue. Just taking prescription medication for low thyroid function will simply just mask the symptoms.
To offer some perspective: up to 95% of the thyroid hypothyroidism in the US is caused not by an iodine deficiency, but occurs as the result of an autoimmune disease so avoiding cruciferous vegetables will do little to fix your underactive thyroid, and may deprive you of valuable healthy benefits such as dietary fiber, and anti-inflammatory, cancer-fighting antioxidants.5
Try this: Cut apples crosswise (don’t peel them—the skin is the richest source of pectin!), dredge in brown sugar, then pan-fry in coconut oil until tender; top with shredded basil and crumbled blue cheese. Spiralize a whole apple with skin, lightly steam in apple juice until tender, and serve with yogurt, hemp seeds, and blueberries as a breakfast noodle bowl. Simmer chopped apples, parsnips, shallots, and sprigs of thyme in broth until tender; remove thyme sprigs and purée until smooth; top with additional thyme and a dollop of crème fraîche.
You may have read that green, leafy veggies like kale, bok choy, broccoli, and Brussels sprouts can make hypothyroidism worse. But before you keep reading, ask yourself a question: Do you live in the United States? That’s key — because if you do, you likely don’t need to worry about these cancer-fighting veggies messing with your hypothyroidism management. (7)
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