Your Thyroid Can Hurt Your Heart

Thyroid Hormones Have Far-Reaching Effects

Your Thyroid Can Hurt Your Heart
Analysis of studies shows that subclinical hypothyroidism
poses substantial risk for coronary artery disease
By Will Block

It is hard to predict—especially the future.
— Niels Bohr

f you’ve ever experienced a serious earthquake (as most Californians have), you know how startling it is and how frightening it can be, especially if you’re in a high-rise building that starts swaying like a tree in a gale. The quake always comes as a total surprise, with no warning whatever. In the news coverage that follows, you hear yet again how stresses in the earth’s crust had been building, slowly but surely, over the years or decades or centuries, showing no outward (or upward) symptoms of the impending, cataclysmic release of all that pent-up energy.

Of course, geophysicists who had been studying the region to determine what was going on deep beneath the surface probably knew that something bad was brewing and that an earthquake was likely to occur at some point in the future. The trick, though, is predicting the date. But that’s impossible—geophysics is too complicated a subject, with too many variables, to allow predictions of this kind.

The Worst Kind of Jolt

The same can be said of physiology, in which (as if you hadn’t seen it coming) there is an analogy with the earthquake scenario. Physicians who detect increasing levels of thyroid-stimulating hormone, which is produced deep beneath our surface (in the pituitary gland), can tell that something bad is brewing in us, even though there may be no outward symptoms of it to alert us to the impending danger.

And what might that danger be? In the worst-case scenario, a heart attack. Like earthquakes, most heart attacks strike suddenly, without warning. If you’re lucky, it’s a relatively minor jolt, and you recover— albeit with a tremendously heightened appreciation for the value of preventive measures, such as regular exercise and a healthy diet. But if your heart attack is the equivalent of an 8 or 9 on the Richter scale, your worries are probably over.

Subclinical Hypothyroidism, a Subtle Disease . . .

The function of thyroid-stimulating hormone (TSH), also known as thyrotropin, is to stimulate the thyroid gland’s production of its principal hormone, thyroxine, which plays a central role in regulating our energy metabolism, among other things. But how can elevated TSH levels predict the likelihood (though never the date) of a heart attack? How, for that matter, can they even predict the likelihood of a heart attack’s common precursor, coronary artery disease, which is a less dramatic but nonetheless serious condition?

To find the answer, we need to go down one more step on the “dramatic-and-serious” scale, to a condition that is—or can be—a precursor to coronary artery disease: subclinical hypothyroidism. This is a subtle disease in which thyroid function is lower than it should be for optimal health, but not so low as to qualify as conventional (clinical) hypothyroidism, an overt disease in which thyroid function is measurably below the normal range.

. . . With a Simple, Precise Definition

Hypothyroidism, commonly known as “low thyroid,” entails a wide range of mostly common symptoms, including sluggishness, weakness, depression, low blood pressure, low heart rate, high cholesterol, weight gain, constipation, aching joints, poor memory, sensitivity to cold, declining libido, dry skin, and brittle nails and hair. In subclinical hypothyroidism, these symptoms are either totally absent or so subdued and gradual in onset that they can easily be overlooked, attributed to something else, or dismissed as elements of “normal aging.”

Here is a more precise definition of subclinical hypothyroidism (let’s call it SCH for short) than that given above: SCH is a disease in which TSH levels are elevated, but thyroxine levels are within the normal range (albeit usually near the low end of that range, as the hypo in hypothyroidism suggests). Clearly, something is amiss with thyroid function when it takes an excessive amount of TSH to produce normal amounts of thyroxine. (For more on this, see the sidebar.)

The Thyroid Gland as a Clogged Air Filter

Consider a furnace of the kind you may very well have in your home. Natural gas is piped into the furnace, where it’s burned, producing carbon dioxide and water vapor. Some of the heat of combustion is transferred, via the heat exchanger, to air that’s drawn in through the inlet duct and expelled via the outlet duct to heat your house. Inside the furnace housing, between these ducts, is an air filter that traps dust from the inlet so that the heated outflow is clean.

With time, the air filter will gradually become clogged. This will retard the airflow and require the furnace to work longer and longer to force enough warm air into your house to maintain the desired temperature. You’ll probably still get all the heat you want (normal output), but it will take more and more gas to provide it (increased input), and you’ll see the evidence of that in your steadily mounting gas bills.

Thyroid function works similarly. Here the pituitary hormone TSH is the incoming “gas,” your thyroid gland is the “furnace,” and the thyroid hormone thyroxine is the outgoing “heat.” As long as your thyroid is functioning normally, your TSH and thyroxine levels will both fall within normal ranges, and you’ll be fine. If, however, some aspect of your thyroid’s inner functioning (the “air filter”) becomes degraded in some way, the biochemical pathway from TSH to thyroxine will become “clogged,” and it will take more and more TSH to stimulate the normal output of thyroxine.

When your TSH levels are elevated but your thyroxine output is normal, you have subclinical hypothyroidism (SCH). You may not know it, but your body knows it, because it has to pay the price (the “gas bill”) for the increasing amounts of TSH in your system.

And what is the price? It’s something far more precious than money: it’s your health, which will gradually be degraded by a poorly functioning thyroid gland. As the article shows, one consequence of SCH is a substantially increased risk for coronary artery disease (CAD), a serious, life-threatening condition.

You can spend a few bucks to replace the air filter in your furnace, but you can’t replace your thyroid gland, nor can you buy your health back. You can, however, maintain it in a better state by supplementing with whole natural thyroid, which might help reduce your risk for CAD.

SCH Should Be Treated

SCH is an age-related disease. Its incidence in the adult population of the United States is estimated to be 4.3%; its prevalence is about 10% in women over 60 years of age, and somewhat less than that in men.1 During the century or so since SCH became recognized as a disease, most physicians believed that it did not require treatment, especially since its symptoms—if any—are so mild. Their lack of concern is giving way, however, to a newfound appreciation for the fact that SCH is a “stealth” disease whose long-term consequences, especially on cardiovascular function, can be severe.


© iStockphoto.com/Karen Grotzinger
Thus, more and more physicians are embracing the idea that SCH should be treated. (See “The Benefits of Whole Natural Thyroid” in the January 2004 issue.) Treatment is exceptionally easy and effective: it usually consists of synthetic thyroxine, which is chemically identical to natural thyroxine. (Both are also called levothyroxine, the form in which thyroxine is found in our bodies.) Most physicians who practice alternative and complementary medicine, however, recommend using extracts of whole natural thyroid from livestock, which contains not just thyroxine but also the other hormones produced by the thyroid gland, in their biologically normal proportions. (As with synthetic thyroxine, the animal hormones are chemically identical to their human counterparts.)

A vexing problem for all physicians is that studies on the association between SCH and cardiovascular disease have been confusing and contradictory. Some studies have shown no association, whereas others have shown strong associations. Among the latter, there has been no universal agreement on which manifestations of cardiovascular disease are associated with SCH, but many of them have pointed to high total cholesterol and LDL-cholesterol (the “bad cholesterol”). Others have pointed to factors such as elevated levels of C-reactive protein (a marker of inflammation that’s implicated in cardiovascular disease) and a state of abnormally increased blood coagulability (a tendency to form clots).

Researchers Separate Wheat from Chaff

Recently a team of researchers from the United States and Switzerland tried to resolve some of the confusion by performing a meta-analysis—a systematic, rigorous analysis of the pooled data from a number of previously published studies; this allows a more nearly definitive conclusion to be reached than is possible from any individual study.1 Their objective was to determine the extent to which SCH is a risk factor for coronary artery disease (CAD), a category of cardiovascular disease that results from obstruction of the coronary arteries.* This life-threatening condition leads to myocardial ischemia, or insufficient blood flow to the heart muscle.


*The authors used the common but imprecise term coronary heart disease (CHD). There is no such thing as a “coronary heart,” and there are many kinds of heart disease that do not involve the coronary arteries.


A search of the literature in English, French, and German between January 1966 and April 2005 turned up 753 reports of potential relevance. Of these, 719 were eliminated for any number of more or less obvious reasons, leaving 34 to be evaluated more closely. In that process, 20 more were eliminated owing to serious flaws in design or execution. That left 14 studies that met the eligibility criteria for inclusion in the meta-analysis. They encompassed a total of 13,011 men and women with SCH, the great majority of whom were 55 or older.

The total number of CAD outcomes recorded was 1362. These outcomes were: heart attack; angina pectoris (chest pain); acute coronary syndrome (an umbrella term used to cover any group of clinical symptoms compatible with acute myocardial ischemia); revascularization (surgical restoration of blood supply to the heart, as a result of CAD); significant coronary stenosis (a narrowing of the cross-sectional area of a coronary artery by 50% or more); and death caused by CAD in particular or cardiovascular disease in general.

SCH Leads to Increased Risk for CAD

Of the 14 studies included in the meta-analysis, most had shown a trend toward an increased risk for CAD in patients with SCH, but these findings reached statistical significance in only four studies. In the meta-analysis, however, the result of pooling all the data (with much number crunching to make them comparable with each other) was that the overall risk for CAD was increased by a substantial 65%.


Physicians’ prior lack of concern
is giving way to a newfound
appreciation for the fact that SCH is
a “stealth” disease whose long-term
consequences can be severe—
and it should be treated.


This appears to provide striking confirmation of what had long been suspected by some, and believed by others, despite the contradictory evidence. That SCH should be linked with CAD in this way is not surprising, considering that thyroid hormones interact strongly with the catecholamine hormones adrenaline and noradrenaline, which play profoundly important roles in cardiovascular function. (See “Stay Heart-Healthy with Thyroid” in the March 2006 issue.)

How to Avoid the Big One

Living in earthquake country, we get used to the fact that the Big One could strike tomorrow or a hundred years from now, and either way, there will be no warning. So we accept the inevitability of it and try to live our lives to the fullest for as long as we are able. For those who have subclinical hypothyroidism, or who think they might have it, it’s a different story: they can do something about their condition and, in so doing, improve their prospects for living healthier, happier, and longer lives.

Reference

  1. Rodondi N, Aujesky D, Vittinghoff E, Cornuz J, Bauer DC. Subclinical hypothyroidism and the risk of coronary heart disease: a meta-analysis. Am J Med 2006;119:541-51.


Will Block is the publisher and editorial director of Life Enhancement magazine.

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