Question 1

A severe systemic illness that causes decreased peripheral conversion of T4 to T3, an increased conversion of T3 to the inactive rT3, and decreased binding of thyroid hormones is known as

Accepted Answer

Euthyroid sick syndrome is hypothyroidism associated with protein-calorie malnutrition, surgical trauma, myocardial infarction, chronic renal failure, diabetic ketoacidosis, anorexia nervosa, cirrhosis, thermal injury, or sepsis. After the underlying cause is treated, the condition is usually resolved.

Question 2

Graves disease is an autoimmune disease in which the thyroid is diffusely enlarged (goiter) and overactive, producing an excessive amount of thyroid hormones. It is the most common cause of hyperthyroidism (overactive thyroid) in the United States. What is the primary target of circulating autoantibodies in this disease?

Accepted Answer

In Graves disease, the TRH receptor itself is the primary autoantigen and is responsible for the manifestation of hyperthyroidism. The thyroid gland is under continuous stimulation by circulating autoantibodies against the TRH receptor, and pituitary TSH secretion is suppressed because of the increased production of thyroid hormones. These thyroid-stimulating antibodies cause release of thyroid hormone and Tg and stimulate iodine uptake, protein synthesis, and thyroid gland growth.

Question 3

Botanical preparations have been found in animal studies to influence thyroid activity. Commiphora mukul (guggulsterones from guggul extract) has strong thyroid stimulatory action, demonstrated by

Accepted Answer

Administration of 1 mg of Commiphora mukul/100 g body weight increases iodine uptake by the thyroid, increases TPO activity, and decreases lipid peroxidation, suggesting that increased peripheral generation of T3 might be mediated by this plant's antioxidant effects.

Question 4

Although some T3 is produced in the thyroid, approximately 80% to 85% is generated outside the thyroid in which organs?

Accepted Answer

T3 is primarily produced by conversion of T4 in the liver and kidneys. The pituitary and nervous system are capable of converting T4 to T3, so they are not reliant on T3 produced in the liver or kidney.

Question 5

Maintaining thyroid hormone function throughout the aging process appears to be an important hallmark of healthy aging. What characteristic is an indicator of thyroid health in centenarians?

Accepted Answer

Because unhealthy aging is associated with a progressively increasing prevalence of organ-specific and nonorgan-specific autoantibodies, the absence of these antibodies may represent a significantly reduced risk for cardiovascular disease and other chronic age-related disorders.

Question 6

Dietary intervention is a key therapeutic tool in managing patients with thyroid disease. In the absence of nutritional deficiencies, what is the main goal of nutritional support?

Accepted Answer

A variety of food antigens could induce antibodies that cross-react with the thyroid gland. A food elimination diet using gluten-free grains and possible elimination of casein, the predominant milk protein, might be considered for patients with hypothyroidism of unexplained origin.

Question 7

Which of these is NOT a product of the thyroid?

Accepted Answer

Reverse T3 (rT3) is derived from T4 through the action of deiodinase. It is an isomer of T3 but is not itself produced by the thyroid.

Question 8

Iodine deficiency is often a culprit in thyroid disorders. However, in which of these thyroid conditions may supplementing with iodine exacerbate the condition?

Accepted Answer

In autoimmune Hashimoto thyroiditis, supplementing with iodine may exacerbate the condition. Because iodine stimulates production of TPO, this in turn increases the levels of TPO antibodies (TPO Abs) dramatically, indicating an autoimmune flare-up. Some people develop symptoms of an overactive thyroid, but others have no symptoms despite tests showing an elevated level of TPO Abs. Therefore, one must be cautious regarding the use of iodine. Furthermore, although iodine deficiency is the most common cause of hypothyroidism for most of the world's population, in the United States and other westernized countries, Hashimoto thyroiditis accounts for the majority of cases.

Question 9

Selenium deficiency, inadequate protein, excess carbohydrates, chronic illness, and stress (high cortisol levels) can all impact what thyroid metabolic process?

Accepted Answer

Changes in 5'-deiodination occur in a number of situations, such as stress, poor nutrition, illness, selenium deficiency, and drug therapy. Toxic metals such as cadmium, mercury, and lead have been associated with impaired hepatic 5'-deiodination in animal models. Free radicals are also involved in inhibition of 5'-deiodinase activity.

Question 10

Polycystic ovary syndrome (PCOS) is characterized by which of the following biochemical and endocrine abnormalities?

Accepted Answer

Biochemical and endocrine abnormalities in women with PCOS include elevated levels of androgens (dehydroepiandrosterone, testosterone, and androstenedione), hyperinsulinemia (which results from insulin resistance), impaired glucose tolerance, and hyperlipidemia. Hyperandrogenism is responsible for many of the symptoms of PCOS, such as reproductive and menstrual abnormalities, hirsutism, and acne.

Question 11

Some plant foods (cauliflower, broccoli, cabbage) exert antithyroid activity through what mechanism?

Accepted Answer

Cyanogenic plant foods (cauliflower, broccoli, cabbage, Brussels sprouts, mustard seed, turnip, radish, bamboo shoot, and cassava) exert antithyroid activity through inhibition of TPO. The hydrolysis of some glucosinolates found in cruciferous vegetables (e.g., progoitrin) may yield goitrin, a compound known to interfere with thyroid hormone synthesis.

Question 12

A rare primary adrenal insufficiency in which insufficient levels of steroid hormones are produced despite adequate levels of the hormone ACTH is known as

Accepted Answer

Addison disease is primary adrenal insufficiency and insufficient levels of steroid hormones are produced despite adequate levels of ACTH. In Cushing syndrome, too much cortisol remains in the bloodstream over a long period of time. Adrenal fatigue is a syndrome caused by the decreased ability of the adrenal glands to respond to stress and is almost always secondary to something else. Euthyroid sick syndrome is hypothyroidism associated with a severe systemic illness.

Question 13

Before 1960, reports surfaced that soy formula-fed infants were developing hypothyroidism. The addition of what supplement to these formulas ameliorated this problem?

Accepted Answer

Soybean, an important source of protein in many developing countries, has goitrogenic properties when iodine intake is limited. The isoflavones, genistein and daidzein, inhibit the activity of TPO and can lower thyroid hormone synthesis. Furthermore, soybean interrupts the enterohepatic cycle of thyroid hormone metabolism. Since the addition of iodine to soy-based formulas in the 1960s, there have been no further reports of hypothyroidism developing in soy formula-fed infants.

Question 14

Thyroid health has been shown to be impacted by the elimination of which foods?

Accepted Answer

A variety of food antigens could induce antibodies that cross-react with the thyroid gland. Eliminating gluten-containing grains has been suggested for treatment of hypothyroidism of unknown origin. Selenium has been shown to enhance thyroid function; mushrooms, barley, and seafood are good sources of selenium.

Question 15

Which of these is NOT required for the production of thyroxine (T4) and triiodothyronine (T3)?

Accepted Answer

The synthesis of T3 and T4 requires tyrosine, a key amino acid involved in the production of thyroid hormone, and the trace mineral iodine. Two additional molecules of iodine bind to the tyrosyl ring in a reaction that involves thyroid peroxidase (TPO), an enzyme. When T4 is released from the thyroid, it is primarily in a bound form with thyroid-binding globulin (TBG), a protein that transports thyroid hormones through the bloodstream but is not required for production.

Question 16

Thyroid health in some adults can be improved by increasing the conversion of T4 to T3. This can be accomplished by

Accepted Answer

Nutritional agents that help support proper deiodination by the type 1 5'-deiodinase enzyme include selenomethionine (as L-selenomethionine) and zinc (as zinc glycinate or zinc citrate). Human studies have repeatedly demonstrated consequent reduced concentrations of thyroid hormones when a zinc deficiency is present. Supplementation with tyrosine does not appear to have a beneficial effect on elevating thyroid hormones. Synthetic flavonoid derivatives can decrease serum T4 concentrations and inhibit both the conversion of T4 to T3 and the metabolic clearance of rT3 by the selenium-dependent 5'-deiodinase. Naturally occurring flavonoids appear to have a similar inhibitory effect. Lipoic acid reduces the conversion of T4 to T3.

Question 17

Low energy, cold hands and feet, fatigue, hypercholesterolemia, muscle pain, depression, and a positive test result for thyroid peroxidase antibodies could all be indicative of what condition?

Accepted Answer

Hashimoto thyroiditis is an autoimmune disorder in which the immune system attacks and destroys the thyroid gland. It is the most common form of hypothyroidism. The TPO Abs test is the most important because TPO is the enzyme responsible for the production of thyroid hormones and the most frequent target of attack in Hashimoto thyroiditis.

Question 18

Characteristics of chronic adrenal stress do NOT include

Accepted Answer

Chronic adrenal stress results in decreased sensitivity to thyroid hormones.

Question 19

More than 90% of people with autoimmune thyroid disease have a genetic defect affecting their ability to metabolize what?

Accepted Answer

Vitamin D is considered a prohormone with antiproliferative, differentiating, and immunosuppressive activities. Vitamin D also appears to work with other nutritional factors to help regulate immune sensitivity and may protect against development of autoantibodies.

Question 20

Cushing syndrome is characterized by weight gain, easy bruising, depression, muscle loss, and weakness. It is caused by

Accepted Answer

In Cushing syndrome, too much cortisol remains in the bloodstream over a long period. The exogenous form occurs when individuals take steroids or other similar medications and ceases when the medication is stopped. Endogenous Cushing syndrome is rare and occurs as the result of a tumor on the adrenal or pituitary gland.

Quiz 31: Medical Nutrition Therapy for Thyroid, Adrenal, and Other Endocrine Disorders