Introduction
In hypothyroidism, the thyroid gland
fails to produce adequate levels of thyroid hormone. Symptoms include
sluggishness, sensitivity to cold, weight gain, depression, dry skin, loss of
hair, excessive menstruation, hoarseness, and goiter (a visible enlargement of the
neck caused by a swollen thyroid gland).
Hashimoto’s
thyroiditis is the most common natural cause of low thyroid
hormone levels. In this autoimmune condition, the body develops antibodies
that attack and gradually destroy the thyroid. A viral infection of the thyroid
can also decrease thyroid hormone production, but the effect is generally mild and
temporary. Finally, iodine deficiency can cause
hypothyroidism, but this seldom occurs in the developed world, where iodine is
routinely added to salt.
In addition to these natural causes, there is still one more common cause of
hypothyroidism: medical treatment for hyperthyroidism (excessive production
of thyroid hormone). People with certain forms of hyperthyroidism receive
treatment with radioactive iodine to inactivate the thyroid gland. This treatment
causes hypothyroidism, which requires lifelong treatment with thyroid replacement
therapy.
Until the 1990s, doctors commonly diagnosed hypothyroidism by conducting laboratory tests to measure thyroid hormone levels in the blood (the T4 level). Normal thyroid levels vary widely among people, so this method could not always correctly identify the disease. A much better lab test, which became available in the 1990s, involves measurement of a hormone called TSH, or thyroid stimulating hormone.
TSH is released by the pituitary gland to control the thyroid
gland. The pituitary gland constantly measures the level of thyroid hormone in the
blood and adjusts TSH levels as necessary to get it right. When thyroid hormone
levels are high, it turns TSH levels down. When thyroid hormone levels are too
low, the pituitary raises TSH levels to stimulate the thyroid. If the thyroid
gland does not respond by raising thyroid hormone levels, the pituitary turns up
the TSH levels even higher. When TSH levels are higher than normal limits, this
means that the thyroid gland is having trouble producing enough thyroid hormone
for the body’s needs. In other words, the person has entered a hypothyroid state
or is about to enter such a state. This method of determining thyroid status has
proved reliable.
Medical treatment for low-thyroid conditions is safe and very effective. Treatment involves the use of a hormone called levothyroxine, or T4. The body actually uses two forms of thyroid, T4 and T3, but in most cases the body easily and automatically converts T4 to T3 in the right proportions. The drug dosage is adjusted by monitoring TSH levels. When the pituitary gland is satisfied, the dose is most likely correct.
Other Proposed Treatments
So-called natural thyroid hormone is popular in alternative medicine. Sold by prescription only under the name Armour Thyroid, this extract of pig thyroid contains both T4 and T3. There is no doubt that Armour Thyroid is as effective as standard synthetic thyroid hormone, and it is a satisfactory choice for those who prefer to use natural treatments. However, there is no evidence that Armour Thyroid is any more effective than standard medications, and there are some concerns that variations in stomach absorption may produce slightly erratic results.
One double-blind study failed to find a combination of synthetic T3 and T4 more effective than synthetic T4 as a treatment for hypothyroidism in regard to well-being, quality of life, or mental function. Another double-blind study failed to find any difference between T4 alone or T3 plus T4 in people whose thyroid had been removed because of thyroid cancer. Another study also failed to find discernible differences between the two treatments regarding mood, fatigue, well-being, or mental function; however, for reasons that are unclear, persons given T3 plus T4 were significantly more likely to prefer the new treatment to their previous care than those who were continued on T4. Unless this was merely a statistical accident, people who received the combined treatment were apparently able to detect some subtle benefit that they could not quite understand.
Other than Armour Thyroid, there are no natural therapies with documented
efficacy for the treatment of hypothyroidism. Treatments that are sometimes
recommended but lack any meaningful scientific support include Bacopa
monniera (brahmi), selenium, traditional Chinese herbal
medicine, vitamin B3, and zinc.
Far too frequently, people with low thyroid levels consume seaweed or iodine supplements in hopes that these supplements will help. However, while iodine deficiency does cause low thyroid levels, taking iodine will not help if one is not deficient in it. (The vast majority of people living in the developed world have plenty of iodine.) Excessive iodine intake can occasionally cause hypothyroidism.
Theory of widespread marginal hypothyroidism. There is little doubt that many cases of marginal hypothyroidism go unidentified, and that occasional tests for thyroid adequacy should be part of routine medical care. However, some proponents of alternative medicine go further and suggest that undiagnosed hypothyroidism is a serious epidemic, causing a high percentage of all the illnesses afflicting modern humans. (One of the best-known books on this theory is Solved: The Riddle of Illness by Stephen E. Langer and James F. Scheer, which was published in 1984.) Supposedly, laboratory tests for thyroid hormone levels are not reliable, and many people have marginally low thyroid levels despite normal lab readings.
These thyroid enthusiasts recommend that people use measurements of basal body temperature and not blood tests to determine whether thyroid levels are adequate. Basal body temperature is measured by placing a thermometer under the armpit before arising in the morning. According to proponents of the marginal hypothyroidism theory, a measurement of lower than about 97.5° Fahrenheit indicates a problem. People with basal body temperature readings below this level and symptoms consistent with hypothyroidism are advised to use Armour Thyroid (or various other animal-source thyroid gland supplements that can be obtained with a bit of work). The net result is supposed to be a great improvement in overall health and the resolution of many illnesses.
However, there are a number of problems with this theory. One is that the majority of women have basal body temperature readings below 97.5° Fahrenheit in the time before ovulation, a fact used in the sympto-thermal method of natural family planning. Many healthy men have normal basal body temperatures below 97.5° Fahrenheit too. Because symptoms consistent with hypothyroidism (such as fatigue, depression, and weight gain) occur in many people, this approach is guaranteed to recommend that enormous numbers of people take thyroid supplements.
Furthermore, the basal body temperature method was developed in the days before TSH levels could be measured, a time in which doctors could measure T4 levels only; there is too great a variation in the normal level of T4 for such tests to have been reliable. However, now that the TSH test has become available, the situation has changed. TSH measurements indicate the body’s own determination of its thyroid hormone level. It is difficult to justify ignoring the body’s own “opinion” in favor of an arbitrary reading on a thermometer. Indeed, when people with normal TSH levels are given thyroid medication, the body responds by lowering its own production of thyroid hormone, essentially fighting this supposedly natural therapy.
Nonetheless, the enthusiasm for thyroid medication continues unabated, and some
alternative medicine physicians continue to maintain that thyroid hormone
supplementation is useful even in the presence of a normal
TSH test. In 2001, a double-blind, placebo-controlled, crossover trial attempted
to evaluate the validity of this theory. Researchers enrolled twenty-two people
with symptoms consistent with hypothyroidism but with normal TSH measurements, and
nineteen healthy people. About one-half of each group was given standard synthetic
thyroid hormone (thyroxine 100 micrograms [this is T4]) for twelve weeks and
placebo for another twelve weeks; the other half received placebo for the first
period and thyroid hormone for the second. Improvement was measured through
questionnaires evaluating general health, emotional well-being, and mental
function.
The results showed that participants with symptoms of low thyroid hormone improved significantly. However, those taking placebo improved just as much. In other words, thyroid hormone proved no more effective than placebo. (The healthy participants showed little response to either placebo or thyroid hormone.)
This study indicates that synthetic human thyroid hormone supplementation (T4) is not helpful for people who have normal TSH but have symptoms that are reminiscent of low thyroid hormone. It did not evaluate the effectiveness of the animal-source thyroid recommended by proponents of the hypothyroid theory and, therefore, does not entirely settle the controversy.
Herbs and Supplements to Use with Caution
Supplementation with iodine will not help the thyroid gland except in people who are iodine-deficient. In Japan, the excessive use of seaweed (such as kelp or bladderwrack) is a fairly common cause of hypothyroidism. For this reason, people with low thyroid hormone levels should not consume excessive amounts of these iodine-rich foods.
Soy and its isoflavones (such as genistein) appear to have numerous
potential effects involving the thyroid gland. When given to people with impaired
thyroid function, soy products have been observed to reduce absorption of thyroid
medication. In addition, some evidence hints that soy isoflavones may directly
inhibit the function of the thyroid gland, although this inhibition may be
significant only in people who are deficient in iodine. However, to make matters
more confusing, studies of healthy humans and animals given soy isoflavones or
other soy products have generally found that soy either had no effect on thyroid
hormone levels or actually increased levels. In view of soy’s complex effects
regarding the thyroid, people with impaired thyroid function should not take large
amounts of soy products except under the supervision of a physician. Iron
supplements may also interfere with thyroid hormone absorption.
Bibliography
Bell, D. S., and F. Ovalle. “Use of Soy Protein Supplement and Resultant Need for Increased Dose of Levothyroxine.” Endocrine Practice 7 (2001): 193-194.
Persky, V. W., et al. “Effect of Soy Protein on Endogenous Hormones in Postmenopausal Women.” American Journal of Clinical Nutrition 75 (2002): 145-153.
Pollock, M. A., et al. “Thyroxine Treatment in Patients with Symptoms of Hypothyroidism but Thyroid Function Tests Within the Reference Range.” British Medical Journal 323 (2001): 891-895.
Regalbuto, C., et al. “Effects of Either LT4 Monotherapy or LT4/LT3 Combined Therapy in Patients Totally Thyroidectomized for Thyroid Cancer.” Thyroid 17 (2007): 323-331.
Walsh, J. P., et al. “Combined Thyroxine/Liothyronine Treatment Does Not Improve Well-Being, Quality of Life, or Cognitive Function Compared to Thyroxine Alone.” Journal of Clinical Endocrinology and Metabolism 88 (2003): 4543-4550.
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