Government regulation of dietary supplements
Dietary supplements are increasingly available to patients as a result of a law that was passed in 1994, the Dietary Supplement Health and Education Act (DSHEA). The act specifies that manufacturers of these products are not required to register their products with the Food and Drug Administration (FDA), not required to provide proof of efficacy or safety, nor obtain FDA approval before before producing or selling dietary supplements. Manufacturers must assure that product labelling is not "not false and misleading." The DSHEA was created to allow customers access to safe dietary supplements, improve the health of Americans, empower customers to make choices about preventative health, and stimulate growth of the industry. It did stimulate growth of the industry. In fact, in 1994 there were approximately 4000 dietary supplements on the market, and today there are approximately 75,000. The industry has grown from a $4 billion per year business to a $25 billion per year business. There are numerous dangers with use of thyroid supplements.
There has been some criticism of the DSHEA since it was enacted in 1994. In 2006, the Dietary Supplement and Non-prescription Drug Consumer Protection Act required reporting of adverse effects associated with the use of dietary supplements. In 2007, the Current Good Manufacturing Practices for the supplement industry required that by June of 2010 manufacturers must have proper controls in place so that supplements are processed in a consistent manner and meet standards for purity, strength, and composition.
There is currently NO role for iodine or dietary supplements for the treatment of hypothyroidism
Desiccated Thyroid Hormone
Armour Thyroid, which is dried pig thyroid glandular tissue, is considered by many to be an alternative treatment to synthetic levothyroxine. Many patients consider this product to be natural, and therefore, better. In truth, however, there are very few studies to support the use of desiccated thyroid hormone in preference to levothyroxine for hypothyroidism. A study from Poland in 1989 compared desiccated thyroid hormone to levothyroxine and found that dried thyroid hormone is ineffective in treating hypothyroidism. In clinical practice, the consistency of this medication is poorly reproducible. This includes Armour thyroid, Naturethroid, etc.
This is an essential element required for thyroid hormone production. Severe iodine deficiency during pregnancy and early infancy can lead to mental retardation. Although iodine deficiency is uncommon in the United States, overall iodine intake is decreasing and actually may not be adequate for pregnant and lactating women. Excess iodine supplementation can cause thyroid dysfunction as well. The American Thyroid Association recommends supplementing 150mcg per day and encourages manufacturers of prenatal vitamins to include iodine. Many patients try taking extra kelp which is known to be rich in iodine. A study by Clark, et al. in 2003 randomized 36 normal thyroid patients to either a placebo, low-, or high-dose kelp. They found a dose-related increase in serum TSH in patients taking the kelp supplements, thus kelp supplements are not recommended since they seem to worsen hypothyroidism. Another study by Amster, et al. in 2007 showed there is potential arsenic toxicity when using herbal over-the-counter kelp supplementation.
Thyroid hormone is composed of iodinated tyrosine residues. Therefore, some have suggested that taking tyrosine may increase thyroid hormone levels. Some internet sources claim these L-tyrosine supplements can boost thyroid hormone levels. There is one study in a small journal Palinkas LA et. Al from 2007 that indirectly evaluated this supplement. They found tyrosine leads to a significant reduction in serum TSH and improvement in mood in winter compared with placebo, while the combined T4-T3 supplement leads to a worsening of mood in summer and no improvement in winter.
The thyroid gland has a large concentration of the element selenium. Selenium deficiency is associated with cancer, impaired immune function, neurodegenerative and age-related disorders and disturbances of the thyroid hormone axis. This medication is considered beneficial for some patients with thyroid disease based on a small study by Gartner et al in 2002 that showed a reduction in thyroid antibodies. This was later followed by a study by Negro et al in 2007 screened 2000 pregnant women to show that women randomized to selenium had lower antibody levels and there was a reduction in postpartum thyroiditis. In 2008 a well designed study by Karanikas et al did not show any benefit of selenium in autoimmune thyroid disease. In a study in 2010 by MacFarquhar et al, the FDA found supplements labeled as 200 mcg/ounce actually contained 200 times the labeled concentration. Two hundred of these patients developed selenium poisoning within two weeks; diarrhea (78%), fatigue (75%), hair loss (72%), joint pain (70%), nail discoloration or brittleness (61%), and nausea (58%)
Bucci el al in 1999 showed that zinc sulfate imporved TSH levels in Down Syndrome patients who had nonautoimmune hypothyroidism and low zinc levels. This is the only study that has studied zinc in terms of thyroid disease.
Deficiency in vitamin A causes thyroid gland hypertrophy and reduces thyroid hormone production. There are small studies in children that show thyroid function improves in patients who receive vitamin A supplementation. There is a narrow therapeutic index for vitamin A levels and excess ingestion can lead to vitamin A toxicity; bleeding, fractures, hair loss, and liver disease.
In animals, iron deficiency reduces thyroid hormone metabolism. In areas of the world with endemic iron deficiency, iron supplementation can improve TSH values.
Soy does cause malabsorption of levothyroxine hormone when it is taken as an oral treatment for hypothyroidism. Soy should be separated from thyroid hormone by at least 4 hours. There is a long list of foods that also prevent proper absorption of thyroid hormone from the gut. Most clinical trials show that soy does not cause any thyroid problems in patients with normal thyroid function.
There are no clinical data to prove that herbs are useful in the treatment of hypothyroidism. There is a long list of herbs found over the counter for the possible treatment of hypothyroidism. Coleus foreskohlii, fucus vesiculosus, guggol, hawthorne, ginseng, astragalus, bitter melon, bupleurum, scullcap, corydalis, dong quai, eluthero, fo-ti, hypericium, green teal, licorice, ligustrum, maitake, reishi, schisandra, shitake, sweet annie, garlic, ginko biloba, horseradish, equisetum arvense, avena sativa, centella asiatica.
AACE/American Thyroid Association guidelines
Iodine supplementation, including kelp, should not be used in the management of hypothyroidism
Kelp should not be used in the treatment of iodine deficiency in pregnant women
Although selenium supplementation may affect the course of autoimmune thyroiditis, it should not be used to prevent or treat hypothyroidism until proven safe.
Patients taking dietary supplements for hypothyroidism should realize that commercially available thyroid-enhancing products are not meant to treat the disease and may have significant side effects.