US Thyroid Epidemic

Whilst being interviewed by Radio New Zealand's Kim Hill, Theo Colborn was quizzed about the endocrine disrupting effects of soy, Colburn made reference to the thyroid "epidemic" that had afflicted infants fed soy formulas in the late 1950's and early 1960's.

The Colorado Thyroid Disease Prevalence Study provides disturbing evidence that the general population in the US is on the brink of an epidemic of  thyroid disease and Soy Online Service believes that the increased use of soy products is to blame:

The Colorado Thyroid Disease Prevalence Study

Arch Intern Med. 2000;160:526-534

Gay J. Canaris, MD, MSPH; Neil R. Manowitz, PhD; Gilbert Mayor, MD; E. Chester Ridgway, MD

Context  The prevalence of abnormal thyroid function in the United States and the significance of thyroid dysfunction remain controversial. Systemic effects of abnormal thyroid function have not been fully delineated, particularly in cases of mild thyroid failure. Also, the relationship between traditional hypothyroid symptoms and biochemical thyroid function is unclear.

Objective  To determine the prevalence of abnormal thyroid function and the relationship between (1) abnormal thyroid function and lipid levels and (2) abnormal thyroid function and symptoms using modern and sensitive thyroid tests.

Design  Cross-sectional study.

Participants  Participants in a statewide health fair in Colorado, 1995 (N = 25,862).

Main Outcome Measures  Serum thyrotropin (thyroid-stimulating hormone [TSH]) and total thyroxine (T₄) concentrations, serum lipid levels, and responses to a hypothyroid symptoms questionnaire.

Results  The prevalence of elevated TSH levels (normal range, 0.3-5.1 mIU/L) in this population was 9.5%, and the prevalence of decreased TSH levels was 2.2%. Forty percent of patients taking thyroid medications had abnormal TSH levels. Lipid levels increased in a graded fashion as thyroid function declined. Also, the mean total cholesterol and low-density lipoprotein cholesterol levels of subjects with TSH values between 5.1 and 10 mIU/L were significantly greater than the corresponding mean lipid levels in euthyroid subjects. Symptoms were reported more often in hypothyroid vs euthyroid individuals, but individual symptom sensitivities were low.

Conclusions  The prevalence of abnormal biochemical thyroid function reported here is substantial and confirms previous reports in smaller populations. Among patients taking thyroid medication, only 60% were within the normal range of TSH. Modest elevations of TSH corresponded to changes in lipid levels that may affect cardiovascular health. Individual symptoms were not very sensitive, but patients who report multiple thyroid symptoms warrant serum thyroid testing. These results confirm that thyroid dysfunction is common, may often go undetected, and may be associated with adverse health outcomes that can be avoided by serum TSH measurement.

For more detail on the The Colorado Thyroid Disease Prevalence Study

The statistics on thyroid disease in the US also tell a disturbing tale.  Since 1990 SEER cancer statistics show that the overall thyroid cancer incidence, across all ages and races in the United States, has been subject to a statistically significant annual increase (1.4 % per annum).   That increase was highest amongst females (1.6 % per annum).  Also worth note is the fact that between 1975 and 1996 the incidence of thyroid cancer has risen 42.1% in the United States.  This increase was particularly notable in women and most recent figures (1996) show that the incidence of thyroid cancer has climbed to 8.0 per 100,000.

And what about children? The incidence of soy-formula feeding is greater in the United States than anywhere else in the world. The National Cancer Institute (NCI) publication 'Cancer Incidence and Survival among Children and Adolescents: United States SEER Program' 1975-1995 has reported that the most prevalent carcinomas in US children and adolescents younger than 20 years were thyroid carcinomas (35.5%); more prevalent than the more publicised melanomas (30.9%). Approximately 75% of the thyroid carcinomas occurred in adolescents aged 15-19 years of age, and NCI note that "the preponderance of thyroid cancer in females suggest that hormonal factors may mediate disease occurrence". Hormonal factors includes agents that affect thyroid hormone status and Soy Online Service believe that soy-formula use in infancy is an hitherto unrecognised risk factor.