April 24, 2008

7 Min Read
Nutrition Q&A with Dan Lukaczer

Q: Can the amino acid carnitine help with my overactive thyroid gland?

A: Yes. Carnitine, also known as L-carnitine (abbreviated for levocarnitine), might help as part of a program to control an overactive thyroid. Carnitine is an amino acid that is synthesized in the liver and kidneys from two other amino acids, lysine and methionine. It can also be consumed preformed, and is found in foods such as meat and dairy. The major function of carnitine in cells is to facilitate the transport and metabolism of long-chain fatty acids for energy generation.

Carnitine appears to have a role in thyroid function, as seen in studies where patients with thyroid dysfunction had low levels of carnitine in their serum and urine.1 It seems to act as a peripheral antagonist of thyroid hormone action. That is, it inhibits the activity of both triiodothyronine (T3) and thyroxine (T4) by preventing their entry into cell nuclei. Thus, it was thought carnitine might help with an overactive thyroid gland that produces too much thyroid hormone—and it does.

A randomized, double-blind, placebo-controlled, six-month trial using 2 g or 4 g/day of oral L-carnitine prevented, minimized or reversed hyperthyroidism-related symptoms such as palpitations and nervousness.2,3 There was no difference between the 2 g vs. 4 g dose. It has also been noted that hyperthyroidism seems to deplete the body's stores of carnitine, so carnitine supplementation might be useful as part of a comprehensive program. One caveat to keep in mind, however: Someone with normal thyroid function who uses carnitine for other reasons might decrease his or her thyroid-hormone activity. I've not seen this reported in the literature, but hypothetically this could become a problem.

Q: I've heard that I should add macadamia nuts to my diet because they lower cholesterol. Would you agree?

A: Tree nuts, in general, seem to have a lipid-lowering effect, and macadamia nuts are no exception. However, I wouldn't say they top the list. In the past few years, numerous studies have found many positive inverse associations between nut consumption and cholesterol. A recent review of studies—three almond (using 50 g to 100 g/day), two peanut (35 g to 68 g/day), one pecan (72 g/day), and four walnut (40 g to 84 g/day)—showed decreases in total cholesterol between 2 percent and 16 percent and decreases in low-density lipoprotein (the "bad" cholesterol) between 2 percent and 19 percent compared with subjects consuming control diets.4

Studies with macadamia nuts are a bit more equivocal. In one study, 17 hypercholesterolemic men were given macadamia nuts (40 g to 90 g/day), equivalent to 15 percent of total daily energy intake, for four weeks. Total cholesterol and LDL cholesterol concentrations decreased by 3 percent and 5.3 percent, respectively, and high-density lipoprotein (the "good" cholesterol) levels increased by a surprising 7.9 percent.5 However, in another study where volunteers were put on three successive different diets for 30 days each—a high-fat diet, the American Heart Association Step 1 diet or a diet high in macadamia nuts—total cholesterol, HDL and LDL were essentially the same on the three diets.6

Macadamia nuts are 75 percent fat by weight, 80 percent of which is monounsaturated, which gives them the highest amount of monounsaturated fatty acids of any food. Macadamia nuts also contain plant sterols, and both monounsaturated fats and plant sterols can lower cholesterol. But while it seems like eating macadamia nuts should have a positive effect, the trials with other nuts seem more promising. So you might want to maintain those, rather than macadamia nuts, in your diet.

Q: Will selenium supplementation help with autoimmune thyroiditis?

A: Research suggests yes, and I have noted this in clinical practice. In autoimmune thyroiditis, the body develops antibodies to the thyroid gland, essentially attacking it. These antibodies can cause numerous symptoms that often have to be controlled with prescription medications.

Various studies have shown that selenium is critically important for thyroid hormone activity—it is involved in the enzyme that helps convert the thyroid hormone T4 to its more active form T3. In areas of the world with severe selenium deficiency, there is a higher incidence of thyroiditis. Even mild selenium deficiency may contribute to the development and continuance of autoimmune thyroid diseases.

In addition, studies have shown that selenium supplementation may improve inflammatory activity in patients with autoimmune thyroiditis, especially in those with high autoimmune activity. Selenium is an essential component of the family of detoxifying enzymes glutathione peroxidase. While the exact mechanism is not well-determined, it might be that selenium's enhancement of detoxifying enzyme activity enforces the defense against oxidative stress and, hence, inflammation. Demonstrating effectiveness, a recent nine-month evaluation showed that at 200 mcg/day, L-selenomethionine, a form of selenium, suppressed serum concentrations of a specific thyroid antibody called TPO in patients with autoimmune thyroiditis. As it turns out, this dose of selenium is the one sufficient to maximize glutathione peroxidase activities.7

Earlier studies showed that 200 mcg/day of selenium given for three or six months also had a salutary effect in thyroiditis.8,9 Whether this effect is specific for autoimmune thyroiditis or may also be effective in other endocrine autoimmune diseases has yet to be investigated.

Q: I've just read that milk thistle may help with diabetes. Is that true?

A: There is some intriguing new research that suggests it might be. The newer study you heard about was probably a randomized, double-blind clinical trial involving 51 people who had had type 2 diabetes for at least two years. One group of 25 patients received 200 mg of milk thistle (Silybum marianum) seed extract three times a day for four months, while the remaining 26 received the same regimen, but were given a placebo tablet instead of the herbal extract. All of the patients also continued to use conventional, oral hypoglycemic treatment during the trial. When compared with the beginning of the trial, the milk thistle treatment group had a significant reduction in fasting blood-glucose levels and a reduction in glycosylated hemoglobin.10

The study seems to support previous work. Animal studies show that Silybum marianum produced a significant decrease of blood-glucose levels in both normal and type 1 diabetic rats without raising insulin levels, suggesting that the herb is somehow improving the action of insulin.11 Milk thistle also has been shown to have a protective effect on pancreatic damage in animal experimental diabetes.12 Other human trials showed administration of milk thistle in patients with type 2 diabetes and compensated chronic alcoholic-liver disease caused a significant decrease in both glucose and triglyceride plasma levels.13 Another trial in cirrhotic diabetic patients showed that treatment with Silybum marianum reduced the lipoperoxidation of cell membranes and insulin resistance, significantly decreasing insulin overproduction and the need for exogenous insulin administration.14 This information seems to be enough to suggest that it would be wise to use milk thistle with diabetics who have compromised liver function.

1.Sinclair C, et al. Muscle carnitine in hypo- and hyperthyroidism. Muscle Nerve 2005;32(3):357-9.
2.Benvenga S, et al. Effects of carnitine on thyroid hormone action. Ann N Y Acad Sci 2004;1033:158-67.
3.Benvenga S, et al. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab 2001;86(8):3579-94.
4.Mukuddem-Petersen J, et al. A systematic review of the effects of nuts on blood-lipid profiles in humans. J Nutr 2005;135(9):2082-9.
5.Garg ML, et al. Macadamia-nut consumption lowers plasma total and LDL cholesterol levels in hypercholesterolemic men. J Nutr 2003;133(4):1060-3.
6.Curb JD, et al. Serumlipid effects of a high-monounsaturated-fat diet based on macadamia nuts. Arch Intern Med 2000;160(8):1154-8.
7.Turker O, et al. Selenium treatment in autoimmune thyroiditis: nine-month follow-up with variable doses. J Endocrinol 2006;190(1):151-6.
8.Gartner R, et al. Selenium supplementation in patients with autoimmune thyroiditis decreases thyroid peroxidase antibodies concentrations. J Clin Endocrinol Metab 2002;87(4):1687-91.
9.Duntas LH, et al. Effects of a six-month treatment with selenomethionine in patients with autoimmune thyroiditis. Eur J Endocrinol 2003;148(4):389-93.
10.Huseini HF,et al. The efficacy of Silybum marianum (L.) Gaertn. (silymarin) in the treatment of type II diabetes: a randomized, double-blind, placebo-controlled clinical trial. Phytother Res 2006;20(12):1036-9.
11.Maghrani M, et al. Study of the hypoglycaemic activity of Fraxinus excelsior and Silybum marianum in an animal model of type 1 diabetes mellitus. J Ethnopharmacol 2004;91(2-3):309-16.
12.Soto CP, et al. Prevention of alloxan-induced diabetes mellitus in the rat by silymarin. Comp Biochem Physiol C Pharmacol Toxicol Endocrinol 1998;119(2):125-9.
13.Lirussi F, et al. Silybin-beta-cyclodextrin in the treatment of patients with diabetes mellitus and alcoholic-liver disease. Efficacy study of a new preparation of an anti-oxidant agent. Diabetes Nutr Metab 2002;15(4):222-31.
14.Velussi M, et al. Long-term (12 months) treatment with an anti-oxidant drug (silymarin) is effective on hyperinsulinemia, exogenous-insulin need and malondialdehyde levels in cirrhotic diabetic patients. J Hepatol 1997;26(4):871-9.

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