Nutrients to Support Thyroid Function
Iodine. The body needs iodine to make thyroid hormone. As of the late 1990s, thirty-two European countries were still affected by iodine deficiency.104 In 2007 the WHO estimated that over 30% of the world’s population (2 billion people) has insufficient iodine intake as measured by urinary iodine excretion below 100 µg/L.105 Iodized salt has proven to be effective at preventing iodine deficiency. The Morton Salt Company began selling iodized salt in the United States in 1924.106
Hypothyroidism in the unborn child, congenital hypothyroidism or cretinism, is frequently caused by iodine deficiency. In industrialized countries the incidence is about 1 case in 4500 live births. Yet, the incidence of cretinism can increase to as much as 1 case in 20 live births in areas that have iodine deficiency.107 Because of this, iodine deficiency remains one of the leading causes of mental retardation.108
During pregnancy T4 production doubles, causing increases in daily iodine requirements.109 Iodine deficient pregnant women cannot produce the thyroid hormones that are needed for proper neurological development of their growing babies, and are at high risk of giving birth to infants with cognitive impairment and learning delay. Even moderate iodine deficiency in a pregnant woman can lower her infant’s IQ from 8 to 16 points.110, 111
People who avoid iodized salt or adhere to a salt-restricted diet may become iodine deficient.112 Vegetarians are also at risk of developing iodine deficiency, especially if they eat food grown in low iodine soil.113 Vegans that avoid sea vegetables, are also at higher risk.114
Diets both low and high in iodine are associated with hypothyroidism. This is supported by studies that have shown that both low and high urinary iodine excretion are associated with hypothyroidism.115 High intake of iodine also increases the risk of Hashimoto’s thyroiditis.116
Iodine or foods high in iodine, such as seaweed, are thought useful in treating hypothyroidism but this is probably only true for people who are iodine deficient.113, 114 The upper intake level (UL) of iodine for adults is 1.1mg per day. However, iodine ingestion above this amount is generally well tolerated.117
The amount of supplemental iodine needed for an individual varies widely based on the factors previously listed. It is important to test thyroid function when supplementing with iodine since both low and excessively high intake can contribute to thyroid dysfunction.
Selenium. After iodine, selenium is probably the next most important mineral affecting thyroid function. The thyroid contains more selenium by weight than any other organ.118 Selenium is a necessary component of the enzymes that remove iodine molecules from T4 converting it into T3; without selenium there would be no activation of thyroid hormone. When patients suffering from various forms of thyroid disease were tested for selenium levels, all were found to be lower than normal healthy people.119 Some researchers suggest that selenium supplementation will improve conversion of T4 to T3.120 Selenium also plays a role in protecting the thyroid gland itself. The cells of the thyroid generate hydrogen peroxide and use it to make thyroid hormone. Selenium protects the thyroid gland from the oxidative damage caused by these reactions. Without adequate selenium, high iodine levels lead to destruction of the thyroid gland cells.121,122
People living in areas with low soil selenium content are more likely to develop Hashimoto's disease.123 This may be because a selenium deficiency makes the enzyme glutathione peroxidase less effective.124 Thus selenium supplementation has been suggested for treating Hashimoto’s disease.125
In a placebo controlled study published in 2002, researchers in Germany reported on an experiment in which they gave 200 mcg of sodium selenite daily to patients with Hashimoto's disease and high levels of thyroid peroxidase antibodies. After three months, the thyroid peroxidase antibody levels of the patients taking selenium were decreased by 66.4% compared to their pre-treatment values, and antibody levels returned to normal in nine of the selenium treated patients.126 Austrian researchers reported in 2008 that they were unable to duplicate the results of the earlier study when they did not limit the study population to those with high levels of thyroid peroxidase antibodies. They suggest that selenium supplementation might be of greater benefit to patients with higher disease activity.127
Selenium deficiency is also common in celiac disease, and this may be the tie-in to increased frequency of thyroid problems with celiac disease.128
During severe or prolonged infection, blood levels of selenium, T4, T3 and TSH decrease and the conversion of T4 to T3 slows, inducing a hypothyroid state.129 Because the enzymes that moderate this conversion require selenium, it has been hypothesized that supplementing extra selenium might prevent this decrease in T3 during illness. Supplying extra selenium may decrease mortality from infection, but it does not normalize thyroid hormone levels.130 It seems that the suppression of T3 during sickness is mediated by cytokines, in particular interleukin-6 (IL-6).131 It may be that IL-6 and other cytokines, generated by the infection, limit production of the selenium-enzymes and interfere with hormone production.
Zinc. Zinc may be helpful in patients with low T3 and may contribute to conversion of T4 to T3. In animal studies, zinc deficiency lowered T3 and free T4 concentrations by approximately 30%. Levels of total T4 were not affected by zinc deficiency.132 In a group of patients with low levels of free T3 and normal T4, but elevated rT3 and mild to moderate Zn deficiency, taking oral zinc supplements for 12 months, normalized the serum free T3 and total T3 levels, decreased the rT3 and normalized TSH levels.133
On the other hand, like iodine, too much zinc may suppress thyroid function.134 Very high doses of zinc interfere with copper absorption and can lead to serious and potentially fatal copper deficiency.135,136,137 Thus it is advised to take copper when supplementing with zinc.
Iron. Iron deficiency hinders manufacture of thyroid hormone by reducing activity of the enzyme thyroid peroxidase. In one study 15.7% of women with subclinical hypothyroidism were iron deficient, compared to only 9.8 % of the control group.138 Iron-deficiency anemia decreases, and iron supplementation improves, the beneficial effects of iodine supplementation.139 Treating iron deficient hypothyroid patients with levothyroxine (T4) along with iron improves their iron deficiency anemia more than treatment with iron alone.140
Copper. An August 2010 study revealed that copper is important for normal brain development and its deficiency leaves the hypothalamus unable to regulate thyroid hormone effectively. Copper deficient pregnant rats give birth to infant rats that produce 48% less T3 than those born from healthy mothers.141
Vitamin E. Vitamin E may reduce the oxidative stress caused by hypothyroidism. In one animal study, vitamin E was shown to protect animals from increased oxidation and thyroid cell damage.142 In another study, vitamin E reduced the amount of thyroid cell replication in animals with induced hypothyroidism.143
Vitamin D. Deficiency of vitamin D may increase risk of autoimmune thyroid disease. When adjusted for age, presence of thyroid antibodies was inversely correlated with vitamin D levels in a group of 642 participants (244 males and 398 females) in New Delhi, India.144 Moreover, other evidence suggests that vitamin D deficiency is more common among individuals with thyroid cancer or thyroid nodules, compared to the general population.145 Given the many benefits of adequate vitamin D, it makes sense to supplement if needed.
Vitamin B12. Hypothyroid patients are often vitamin B12 deficient. In a 2008 paper, Pakistani doctors reported that of 116 hypothyroid patients tested for vitamin B12, approximately 40% were deficient.146 It is not clear what the link between B12 deficiency and low thyroid function is, nor if thyroid function will improve with B12 supplementation.147 But, since low B12 causes serious neurologic damage, all hypothyroid patients should be tested.
DHEA and Pregnenolone. Japanese researchers reported that concentrations of DHEA, DHEA-sulfate, and pregnenolone-sulfate are significantly lower in hypothyroid patients compared to age and sex matched healthy controls.148
Turmeric (Curcuma longa) Extract. A 2002 study, using rats, found that treatment with turmeric extract reduced the impact of chemically induced hypothyroidism in terms of thyroid weight, T4, T3 and cholesterol levels.149 Results of a similar trial on rats treated with vitamin E and curcumin, a component found in turmeric, showed that treatment prevented a decline in basal body temperature and protected the liver.150
Rhodiola rosea. Given the fact that stress can influence thyroid status, it may be beneficial for some individuals with hypothyroidism to consider adaptogenic herbs such as Rhodiola.151,152 Adaptogenic herbs support the adrenal glands and can improve the body’s response to stress.153