A large population study published in Archives of Internal Medicine (2000;160:526–534) found that as many as 13 million Americans may have undiagnosed thyroid disease. Among more than 25,000 participants screened, nearly 12% had abnormal TSH levels. About 9.5% were hypothyroid and just over 2% were hyperthyroid. Overall, nearly 10% of participants had a thyroid disorder that had never been diagnosed.
Hypothyroidism was far more common in women and increased steadily with age after 34. The researchers also noted that even mild reductions in thyroid function can raise cholesterol levels. Based on these findings, the authors estimated that up to 10% of Americans with high cholesterol may have underlying, unrecognized hypothyroidism.
More recent surveys continue to suggest that thyroid disease remains underdiagnosed in the United States, particularly among women and older adults. Because symptoms can be subtle and testing may rely too heavily on TSH alone, many cases may still go undetected. These findings highlight why thyroid function should be considered when patients present with fatigue, unexplained weight gain, depression, or elevated cholesterol.
