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Nutraceutical Supplements in the Thyroid Setting: Health Benefits beyond Basic Nutrition
Published: 13 September 2019
Abstract:
In recent years, there has been a growing interest in nutraceuticals, which may be considered as an efficient, preventive, and therapeutic tool in facing different pathological conditions, including thyroid diseases.
Although iodine remains the major nutrient required for the functioning of the thyroid gland, other dietary components play important roles in clinical thyroidology—these include selenium, l-carnitine, myo-inositol, melatonin, and resveratrol—some of which have antioxidant properties. The main concern regarding the appropriate and effective use of nutraceuticals in prevention and treatment is due to the lack of clinical data supporting their efficacy.
Another limitation is the discrepancy between the concentration claimed by the label and the real concentration. This paper provides a detailed critical review on the health benefits, beyond basic nutrition, of some popular nutraceutical supplements, with a special focus on their effects on thyroid pathophysiology and aims to distinguish between the truths and myths surrounding the clinical use of such nutraceuticals.
Carnitine and Thyroid Function:
A German group of authors conducted pivotal clinical studies as early as 1959 in a very limited number of patients with Graves’ disease, using a mixture of the two isomers (l-and d-carnitine) [33]. The first patient was a 53-year-old bedridden woman with very severe Graves’ disease and nervousness, insomnia, weight loss, sweating, tachycardia and Graves’ orbitopathy. Basal metabolic rate (BMR) was +82%, and she was administered 1 g/d d,l-carnitine. After 10 days, BMR was unchanged but one week later it fell to +59%. Five weeks after starting d,l-carnitine, BMR was still +50% and the authors switched to the naturally occurring l-carnitine. After only 10 days BMR dropped more rapidly to +8% with associate improvement in general well-being and heart rate. Atrial fibrillation disappeared and heart rate was 80–90 beats/min. To prove that the improvement was due to l-carnitine, it was withdrawn in the 7th week from admission. BMR rose to +39%, but after rechallenge with l-carnitine it fell again to +18% [33].
In the English-language literature, the first three monotherapy carnitine-treated hyperthyroid patients were reported in the mid-1960s [34]. The authors found that patients became clinically euthyroid without any consistent changes in the thyroid function tests, thus supporting the notion that the antithyroid effect of carnitine is one of peripheral antagonism of thyroid hormone, rather than a direct inhibition of thyroid gland function [35]. This was consistent with human tissue culture experiments where l-carnitine inhibited both cell entry and, to a greater extent, nuclear entry of both T3 and T4 [36]. These data are consistent with carnitine being a peripheral antagonist of thyroid hormone action, with a site of inhibition at or before the nuclear envelope [36].
….
More recent cases of severe forms of Graves’ disease-related hyperthyroidism, including thyroid storms, were treated successfully with l-carnitine [38–40]. Recently, a pilot study indicated the beneficial effects of a combination of l-carnitine and selenium supplementation in subclinical hyperthyroidism [41]. A rationale for a beneficial effect of l-carnitine supplementation in hyperthyroid patients seems likely because increased levels of thyroid hormones deprive the tissue deposits of l-carnitine itself [42], which is further substantiated by the finding of decreased concentrations of carnitine in the skeletal muscles of hyperthyroid patients. Interestingly, trendwise decreased concentrations of carnitine were found in skeletal muscles of hypothyroid patients [43], which were restored upon regaining euthyroidism. Therefore, decreased concentrations of carnitine in skeletal muscles may contribute to myopathy associated with either hypothyroidism or hyperthyroidism.
Sixty thyroid-hormone adequately replaced hypothyroid Korean patients (age 50.0 9.2 years, 57 females) continued to complain of fatigue [44]. These patients were given l-carnitine (990 mg l-carnitine twice daily; n = 30) or placebo (n = 30) for 12 weeks. After 12 weeks, although neither the fatigue severity score nor the physical fatigue score changed significantly after 12 weeks, but the mental fatigue score was significantly improved by treatment with l-carnitine compared with placebo (p < 0.01). In subgroups, both the physical and mental fatigue scores improved significantly in patients younger than 50 years and those with free T3 4.0 pg/mL by treatment with l-carnitine compared with placebo. Other case-based studies have indicated a benefit from l-carnitine on hypothyroid symptoms, but all of them have been case-based [45], while other studies may support benefits in the corticosteroid hormone setting [46].
Published: 13 September 2019
Abstract:
In recent years, there has been a growing interest in nutraceuticals, which may be considered as an efficient, preventive, and therapeutic tool in facing different pathological conditions, including thyroid diseases.
Although iodine remains the major nutrient required for the functioning of the thyroid gland, other dietary components play important roles in clinical thyroidology—these include selenium, l-carnitine, myo-inositol, melatonin, and resveratrol—some of which have antioxidant properties. The main concern regarding the appropriate and effective use of nutraceuticals in prevention and treatment is due to the lack of clinical data supporting their efficacy.
Another limitation is the discrepancy between the concentration claimed by the label and the real concentration. This paper provides a detailed critical review on the health benefits, beyond basic nutrition, of some popular nutraceutical supplements, with a special focus on their effects on thyroid pathophysiology and aims to distinguish between the truths and myths surrounding the clinical use of such nutraceuticals.
Carnitine and Thyroid Function:
A German group of authors conducted pivotal clinical studies as early as 1959 in a very limited number of patients with Graves’ disease, using a mixture of the two isomers (l-and d-carnitine) [33]. The first patient was a 53-year-old bedridden woman with very severe Graves’ disease and nervousness, insomnia, weight loss, sweating, tachycardia and Graves’ orbitopathy. Basal metabolic rate (BMR) was +82%, and she was administered 1 g/d d,l-carnitine. After 10 days, BMR was unchanged but one week later it fell to +59%. Five weeks after starting d,l-carnitine, BMR was still +50% and the authors switched to the naturally occurring l-carnitine. After only 10 days BMR dropped more rapidly to +8% with associate improvement in general well-being and heart rate. Atrial fibrillation disappeared and heart rate was 80–90 beats/min. To prove that the improvement was due to l-carnitine, it was withdrawn in the 7th week from admission. BMR rose to +39%, but after rechallenge with l-carnitine it fell again to +18% [33].
In the English-language literature, the first three monotherapy carnitine-treated hyperthyroid patients were reported in the mid-1960s [34]. The authors found that patients became clinically euthyroid without any consistent changes in the thyroid function tests, thus supporting the notion that the antithyroid effect of carnitine is one of peripheral antagonism of thyroid hormone, rather than a direct inhibition of thyroid gland function [35]. This was consistent with human tissue culture experiments where l-carnitine inhibited both cell entry and, to a greater extent, nuclear entry of both T3 and T4 [36]. These data are consistent with carnitine being a peripheral antagonist of thyroid hormone action, with a site of inhibition at or before the nuclear envelope [36].
….
More recent cases of severe forms of Graves’ disease-related hyperthyroidism, including thyroid storms, were treated successfully with l-carnitine [38–40]. Recently, a pilot study indicated the beneficial effects of a combination of l-carnitine and selenium supplementation in subclinical hyperthyroidism [41]. A rationale for a beneficial effect of l-carnitine supplementation in hyperthyroid patients seems likely because increased levels of thyroid hormones deprive the tissue deposits of l-carnitine itself [42], which is further substantiated by the finding of decreased concentrations of carnitine in the skeletal muscles of hyperthyroid patients. Interestingly, trendwise decreased concentrations of carnitine were found in skeletal muscles of hypothyroid patients [43], which were restored upon regaining euthyroidism. Therefore, decreased concentrations of carnitine in skeletal muscles may contribute to myopathy associated with either hypothyroidism or hyperthyroidism.
Sixty thyroid-hormone adequately replaced hypothyroid Korean patients (age 50.0 9.2 years, 57 females) continued to complain of fatigue [44]. These patients were given l-carnitine (990 mg l-carnitine twice daily; n = 30) or placebo (n = 30) for 12 weeks. After 12 weeks, although neither the fatigue severity score nor the physical fatigue score changed significantly after 12 weeks, but the mental fatigue score was significantly improved by treatment with l-carnitine compared with placebo (p < 0.01). In subgroups, both the physical and mental fatigue scores improved significantly in patients younger than 50 years and those with free T3 4.0 pg/mL by treatment with l-carnitine compared with placebo. Other case-based studies have indicated a benefit from l-carnitine on hypothyroid symptoms, but all of them have been case-based [45], while other studies may support benefits in the corticosteroid hormone setting [46].