Stress, besides suppressing the TSH, acts in other ways to suppress the real thyroid function. Cortisol, for example, inhibits the conversion of T4 to T3, which is responsible for the respiratory production of energy and carbon dioxide. Adrenaline, besides leading to increased production of cortisol, is lipolytic, releasing the fatty acids which, if they are polyunsaturated, inhibit the production and transport of thyroid hormone, and also interfere directly with the respiratory functions of the mitochondria. Adrenaline decreases the conversion to T4 to T3, and increases the formation of the antagonistic reverse T3 (Nauman, et al., 1980, 1984).
During the night, at the time adrenaline and free fatty acids are at their highest, TSH usually reaches its peak. TSH itself can produce lipolysis, raising the level of circulating free fatty acids. This suggests that a high level of TSH could sometimes contribute to functional hypothyroidism, because of the antimetabolic effects of the unsaturated fatty acids.
These are the basic reasons for thinking that the TSH tests should be given only moderate weight in interpreting thyroid function.
The metabolic rate is very closely related to thyroid hormone function, but defining it and measuring it have to be done with awareness of its complexity.
The basal metabolic rate that was commonly used in the 1930s for diagnosing thyroid disorders was usually a measurement of the rate of oxygen consumption, made while lying quietly early in the morning without having eaten anything for several hours. When carbon dioxide production can be measured at the same time as oxygen consumption, it's possible to estimate the proportion of energy that is being derived from glucose, rather than fat or protein, since oxidation of glucose produces more carbon dioxide than oxidation of fat does. Glucose oxidation is efficient, and suggests a state of low stress.
The very high adrenaline that sometimes occurs in hypothyroidism will increase the metabolic rate in several ways, but it tends to increase the oxidation of fat. If the production of carbon dioxide is measured, the adrenaline/stress component of metabolism will be minimized in the measurement. When polyunsaturated fats are mobilized, their spontaneous peroxidation consumes some oxygen, without producing any usable energy or carbon dioxide, so this is another reason that the production of carbon dioxide is a very good indicator of thyroid hormone activity. The measurement of oxygen consumption was usually done for two minutes, and carbon dioxide production could be accurately measured in a similarly short time. Even a measurement of the percentage of carbon dioxide at the end of a single breath can give an indication of the stress-free, thyroid hormone stimulated rate of metabolism (it should approach five or six percent of the expired air).
Increasingly in the last several years, people who have many of the standard symptoms of hypothyroidism have told me that they are hyperthyroid, and that they have to decide whether to have surgery or radiation to destroy their thyroid gland. They have told me that their symptoms of “hyperthyroidism,” according to their physicians, were fatigue, weakness, irritability, poor memory, and insomnia.
They didn't eat very much. They didn't sweat noticeably, and they drank a moderate amount of fluids. Their pulse rates and body temperature were normal, or a little low.
Simply on the basis of some laboratory tests, they were going to have their thyroid gland destroyed. But on the basis of all of the traditional ways of judging thyroid function, they were hypothyroid.
Broda Barnes, who worked mostly in Fort Collins, Colorado, argued that the body temperature, measured before getting out of bed in the morning, was the best basis for diagnosing thyroid function.
Fort Collins, at a high altitude, has a cool climate most of the year. The altitude itself helps the thyroid to function normally. For example, one study (Savourey, et al., 1998) showed an 18% increase in T3 at a high altitude, and mitochondria become more numerous and are more efficient at preventing lactic acid production, capillary leakiness, etc.
In Eugene during a hot and humid summer, I saw several obviously hypothyroid people whose temperature seemed perfectly normal, euthyroid by Barnes' standards. But I noticed that their pulse rates were, in several cases, very low. It takes very little metabolic energy to keep the body at 98.6 degrees when the air temperature is in the nineties. In cooler weather, I began asking people whether they used electric blankets, and ignored their temperature measurements if they did.
The combination of pulse rate and temperature is much better than either one alone. I happened to see two people whose resting pulse rates were chronically extremely high, despite their hypothyroid symptoms. When they took a thyroid supplement, their pulse rates came down to normal. (Healthy and intelligent groups of people have been found to have an average resting pulse rate of 85/minute, while less healthy groups average close to 70/minute.)
The speed of the pulse is partly determined by adrenaline, and many hypothyroid people compensate with very high adrenaline production. Knowing that hypothyroid people are susceptible to hypoglycemia, and that hypoglycemia increases adrenaline, I found that many people had normal (and sometimes faster than average) pulse rates when they woke up in the morning, and when they got hungry. Salt, which helps to maintain blood sugar, also tends to lower adrenalin, and hypothyroid people often lose salt too easily in their urine and sweat. Measuring the pulse rate before and after breakfast, and in the afternoon, can give a good impression of the variations in adrenalin. (The blood pressure, too, will show the effects of adrenaline in hypothyroid people. Hypothyroidism is a major cause of hypertension.)
But hypoglycemia also tends to decrease the conversion of T4 to T3, so heat production often decreases when a person is hungry. First, their fingers, toes, and nose will get cold, because adrenalin, or adrenergic sympathetic nervous activity, will increase to keep the brain and heart at a normal temperature, by reducing circulation to the skin and extremities. Despite the temperature-regulating effect of adrenalin, the reduced heat production resulting from decreased T3 will make a person susceptible to hypothermia if the environment is cool.
Since food, especially carbohydrate and protein, will increase blood sugar and T3 production, eating is “thermogenic,” and the oral (or eardrum) temperature is likely to rise after eating.
Blood sugar falls at night, and the body relies on the glucose stored in the liver as glycogen for energy, and hypothyroid people store very little sugar. As a result, adrenalin and cortisol begin to rise almost as soon as a person goes to bed, and in hypothyroid people, they rise very high, with the adrenalin usually peaking around 1 or 2 A.M., and the cortisol peaking around dawn; the high cortisol raises blood sugar as morning approaches, and allows adrenalin to decline. Some people wake up during the adrenalin peak with a pounding heart, and have trouble getting back to sleep unless they eat something.
If the night-time stress is very high, the adrenalin will still be high until breakfast, increasing both temperature and pulse rate. The cortisol stimulates the breakdown of muscle tissue and its conversion to energy, so it is thermogenic, for some of the same reasons that food is thermogenic.
After eating breakfast, the cortisol (and adrenalin, if it stayed high despite the increased cortisol) will start returning to a more normal, lower level, as the blood sugar is sustained by food, instead of by the stress hormones. In some hypothyroid people, this is a good time to measure the temperature and pulse rate. In a normal person, both temperature and pulse rate rise after breakfast, but in very hypothyroid people either, or both, might fall.
Some hypothyroid people have a very slow pulse, apparently because they aren't compensating with a large production of adrenalin. When they eat, the liver's increased production of T3 is likely to increase both their temperature and their pulse rate.
By watching the temperature and pulse rate at different times of day, especially before and after meals, it's possible to separate some of the effects of stress from the thyroid-dependent, relatively “basal” metabolic rate. When beginning to take a thyroid supplement, it's important to keep a chart of these measurements for at least two weeks, since that's roughly the half-life of thyroxine in the body. When the body has accumulated a steady level of the hormones, and begun to function more fully, the factors such as adrenaline that have been chronically distorted to compensate for hypothyroidism will have begun to normalize, and the early effects of the supplementary thyroid will in many cases seem to disappear, with heart rate and temperature declining. The daily dose of thyroid often has to be increased several times, as the state of stress and the adrenaline and cortisol production decrease.