Thyroid Hormones
Are Not Taken from Mad Cows

elevision images last year of cows in England staggering helplessly and toppling over gave us our first glimpse of what became two epidemics: one, a terrible disease, the other, a media hysteria. The two were merged in hellish images of enormous funeral pyres as the slaughtered cows were incinerated to destroy the virulent organism that had infected them - or that might have. Many were slaughtered needlessly as waves of panic gripped a nation, then spread beyond its shores. Worldwide, the number of slaughtered cows has reached the millions.

The disease, of course, was bovine spongiform encephalopathy (BSE), commonly called mad cow disease. It literally rots the brain, leaving it increasingly riddled with holes, spongelike, until death inevitably claims the victim. BSE is related to a sheep and goat disease called scrapie (so called because the animals scrape themselves raw in an effort to relieve persistent itching). Most terrifyingly, however, it has a human equivalent, called new variant Creutzfeldt-Jakob disease (nvCJD), which can be contracted by eating meat that is contaminated with neural tissue from an infected animal.1 Like BSE, this disease eats away at the brain, leading to severe dementia, and it is invariably fatal. Who in his right mind would not fear such a terrible end?

Why on earth are we talking about this? Because people are legitimately concerned about the possibility of ingesting any animal product that could conceivably have come from an infected source. That includes natural thyroid hormone supplements, which come from bovine thyroid glands. The question then is: where did that bovine come from? Please say "Not England."

Not England. In fact, the source of the hormones in certain supplements is, and always has been, New Zealand, an extremely isolated (and beautiful) island nation on the opposite side of the globe from England. New Zealand has never had a case of BSE, and the government there has stringent measures in place to ensure that it never does (see the sidebar). Natural hormone supplements from New Zealand livestock are as safe as they can possibly be.

Now that that's settled, let us look a little further into the story. In Europe, people's worst fears were realized when, despite efforts to prevent it, BSE crossed the English Channel and began infecting livestock on the continent. Then their worst fear became that it would spread like wildfire. It did not, however, apparently because aggressive efforts to contain it before it could get out of hand were successful.

Meanwhile, the United States, which has the advantage of being separated from England by the Atlantic Ocean, has remained unaffected by the disease. So has New Zealand, which is about as far from England as it's possible to get. Isolation alone is not sufficient to ensure safety, however, because the disease can be carried by livestock feed that was made from infected livestock. That's right - cows in some countries are forced to be cannibals, because they're given bone meal made from the ground-up carcasses of other cows (also sheep). When they eat the tainted meal, they can become infected themselves.

To prevent the disease from spreading, both the USA and New Zealand (and many other countries as well) have long had regulations in place prohibiting the importation of such feed from foreign sources. And in 1997, the FDA banned the use of domestic cattle feed made with the remains of other animals, so our cattle can no longer even eat their American cousins. That protects both them and us. We can safely eat our American burgers and steaks - and we can safely take our New Zealand thyroid supplements. We know why we like to do the former, but why should some of us do the latter?

The thyroid gland, that small lump of tissue near the windpipe at the base of your throat, is involved in some major activities in your body. For example, it plays vital roles in energy metabolism (and thus has some measure of control over weight gain, energy levels, and cold tolerance), mood disorders (such as seasonal affective disorder), and the cardiovascular system.

The thyroid exerts its influence through the secretion of four hormones, cleverly labeled T1, T2, T3, and T4. The two most important of these are T3 (triiodothyronine) and T4 (thyroxine), which contain three and four atoms of iodine, respectively. The most active of the four is T3, most of which is produced by conversion from T4 in the body. When these hormones are produced in low amounts - a condition called hypothyroidism - numerous health problems can ensue, including fatigue, mood swings, weight gain, low blood pressure, elevated cholesterol levels, and painful joints. Sadly, a deficiency in thyroid hormone production is a natural part of growing older; women over the age of 40 are the most likely to be affected, although men are also susceptible.

Usually the condition is mild enough that it manifests itself only as the kinds of symptoms just described, but not in the results of lab tests for thyroid function. This is called subclinical hypothyroidism, and it is often overlooked by physicians or written off as a "normal" part of aging. That's the bad news. The good news is that virtually all instances of age-related thyroid deficiency are easy to address. All it takes is thyroid hormones. But which ones? And are all sources of thyroid hormones alike?

Thyroid hormones can be either naturally or synthetically derived. Unfortunately, synthetic formulations, such as the widely prescribed drug Synthroid®, contain only T4 and therefore do not match the complex profile of natural thyroid derived from the glandular extracts of animals (usually cows), which provide maximum benefits.* Moreover, if the body's ability to convert T4 to T3 is impaired (which occurs in some people owing to the lack of a certain enzyme activity), then the benefit of a drug consisting of T4 alone is limited. Not surprisingly, many researchers believe that all four of the thyroid hormones play some role in our health (otherwise, why would we have them?), so supplementation with all four makes sense. The animal extracts have the same biological activity as that of human thyroid, by the way, because the molecular structures of the animal hormones are the same as those of the human hormones.

*Synthroid is currently facing possible withdrawal from the U.S. market. It is a 48-year-old drug that has not had to face the close scrutiny now placed on pharmaceutical products, and thus lacks FDA approval. Pending the application and approval process, the FDA is expected to act on Synthroid later this summer.2

To minimize the risk of mad cow disease (BSE) spreading to the United States, federal regulatory agencies acted prudently and decisively. In 1989, five years before the first case of nvCJD was diagnosed in the United Kingdom, the U.S. Department of Agriculture banned the importation of live ruminants and most ruminant products from countries with known cases of BSE. As a result, there has never been a case of BSE or nvCJD in the United States. To widen the margin of safety, neuropathological examinations have been performed on over 12,000 American cows displaying neurological symptoms (such as difficulties in walking) that are consistent with BSE. Not a single case of the disease has been found. Thus, all current information indicates that American livestock are free of BSE.

On an equally important front, the American Red Cross is taking measures to ensure that our blood supply is not contaminated with BSE, so as to minimize the risk of transmitting nvCJD through blood transfusions. As of April 17, 2001, the Red Cross no longer accepts blood donations from individuals who had spent more than six months cumulatively in Great Britain between 1980 and 1996.3 It will also defer donations from individuals who received bovine insulin since 1980. The Red Cross also reports that its blood supply is free of BSE and nvCJD.

While these protective measures are reassuring, they cannot guarantee ultimate safety, because there is no such thing. The federal government still allows the rendering of animal carcasses to bone meal, which may be fed to chickens and pigs, but not to cows. In one well-publicized case in January of 2001, however, someone at Purina Mills in Texas accidentally allowed some animal protein to get into a batch of cattle feed, sparking legitimate concern for public health. It turned out that 1222 cows had received the feed. All of them were quarantined and examined, but there were no signs of BSE. Nonetheless, Purina then paid to have the cows destroyed.4 That may have been unnecessary, but it was a good public relations gesture toward a public that had been conditioned by media hysteria to hold unfounded fears of the landing of mad cows on American soil.

Regarding the potential threat of BSE, we should be highly vigilant, but not hysterical, while remaining focused on actual life-and-death issues, as opposed to fears about an exotic disease that does not even exist within our shores. Consider, for example, that ordinary food-borne pathogens, such as Salmonella and E. coli, kill about 5000 Americans every year. And they are just the tip of that particular iceberg - those same pathogens cause about 325,000 hospitalizations and 76 million illnesses annually.5 Talk about social and economic impact! Many food-borne diseases have, of course, already been eliminated, thanks to pasteurization and other scientific methods of safe food processing, but we still have far to go in protecting ourselves from all the dangers that we know are out there.

Meanwhile, we can envy New Zealanders their splendid isolation and take comfort in knowing how healthy and contented their cows are. As long as things stay that way - and it certainly looks as though they will - you can be assured of getting only the safest natural thyroid hormones to help keep you healthy as well.


  1. Roos RP. Controlling new prion diseases. New Engl J Med 2001;344:1549-51.
  2. Reuters Health, New York, June 1, 2001.
  3. American Red Cross, news release, March 6, 2001.
  4. Enserink M. Infectious disease: is the U.S. doing enough to prevent mad cow disease? Science 2001;292:1639-41.
  5. Mead PS, Slutsker L, Dietz V, et al. Food-related illness and death in the United States. Emerging Infectious Diseases 1999;5:607-25.

New Zealand Government's Affidavit on BSE
In March 2001, the New Zealand Ministry of Agriculture and Forestry released a statement declaring that bovine spongiform encephalopathy (BSE) has never been detected in that country, and that it is also free of scrapie. The government banned the importation of live cattle from the United Kingdom in 1988, and it has not allowed the importation of meat or bone meal for incorporation into domestic livestock feed for decades. It has also banned the feeding of any ruminant tissues to other ruminants.

To further ensure that New Zealand cattle products remain free of BSE, the government has also banned the importation of bovine embryos from the United Kingdom and some other countries, live cattle from Europe in general, and other products from various sources that could pose the risk of BSE infection. It should also be reassuring to know that New Zealand ranchers rely predominantly on grazing in raising their livestock. Thus, New Zealand cows get their nutrients from the source that nature intended.

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