Why Are So Many People Getting Thyroid Disease?

Estimates of the Frequency of Thyroid Disease Vary Widely

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One question thyroid patients frequently ask is "Why are so many people getting thyroid disease?"

Let's take a look at the issue.

The first issue is really whether thyroid disease on the rise, or it's an issue of how you view the numbers. There is a huge discrepancy among experts as to how many thyroid patients there are in the United States. Some organizations still cite 13 million as the total number of thyroid sufferers.

More recently, some groups estimate that 27 million Americans have thyroid disease, and about 13 million of them are undiagnosed. (Reference).

The issue is further complicated by the fact that the medical community still can not agree on what the normal reference range is for the Thyroid Stimulating Hormone (TSH) test. Since 2002, some groups have recommended narrowing the reference range from .5 - 5.0 to .3 to 3.0. If that narrower range were used, according to researchers:

"...using a TSH upper normal range of 5.0, approximately 5% of the population is hypothyroid. However, if the upper portion of the normal range was lowered to 3.0, approximately 20% of the population would be hypothyroid..." (Reference)

That would mean that as many as 60 million Americans fall outside the TSH reference range and thus could conceivably be diagnosed with thyroid disease.

Very limited epidemiology has been done on thyroid disease, and as noted, estimates tend to vary wildly, so it's difficult to say if thyroid disease in general is on the rise, or more people and practitioners are aware of it and therefore getting diagnosed.

We do know, however, that the majority of people with thyroid disease in the U.S. have an underlying autoimmune thyroid disease that is causing their condition. And autoimmune diseases are definitely on the rise. (Reference). So it makes sense that with more autoimmunity, there will be an increase in thyroid disease as a result.

One thing we do know: thyroid cancer is on the rise. According to the American Cancer Society, (Reference): around 56,460 new cases of thyroid cancer (43,210 in women, and 13,250 in men) will be diagnosed in 2012. "The chance of being diagnosed with thyroid cancer has risen in recent years and is now more than twice what it was in 1990. Some of this is the result of the increased use of thyroid ultrasound, which can detect small thyroid nodules that might not otherwise have been found in the past. Still, at least part of the increase is from finding more large tumors as well."

Risk Factors for Thyroid Disease

What can be contributing to the rise in autoimmune diseases, thyroid problems, and thyroid cancer? Experts have a number of theories, but no hard answers.

We know that chemicals and toxins in the environment are linked to increased risk of thyroid disease. Some of the culprits include perchlorate, pesticides, phthalates like bisphenol-A (BPA), and thyroid-disrupting endocrine disruptors, also known as environmental estrogens.

Radiation and nuclear exposure are also risk factors that can trigger thyroid problems in some people. The radiation exposure that resulted from the Chernobyl disaster was a major trigger of thyroid disease, and experts expect to see similar effects down the road after Japan's Fukushima meltdown.

People who have had medical treatments involving radiation to the head and neck area (e.g., treatment for Hodgkin's disease, nasal radium therapy, radiation to tonsils and neck area) are also at increased risk of thyroid problem. Even multiple dental x-rays have been linked to an increased risk of thyroid disease.

Viruses can attack tissues and organs, and trigger autoimmune diseases and inflammatory thyroid conditions, and certain bacteria --the foodborne bacteria Yersinia enterocolitica for example -- are linked to thyroid risks.

Other controllable risk factors that may be responsible in part for increasing rates of thyroid disease include the following:

Thyroid disease seems on be on the rise, with more people diagnosed with autoimmune thyroid problems, and increasing rates of thyroid cancer. What risk factors, behaviors, or environmental issues do you believe are contributing to or causing the increases in thyroid problems in the U.S. and around the world?

Blackwell J. "Evaluation and treatment of hyperthyroidism and hypothyroidism." J Am Acad Nurse Pract. 2004 Oct;16(10):422-5.

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