The National Institutes of Health (NIH) states that five out of every 100 Americans over the age of 12 have hypothyroidism. The prevalence of this disease increases with age.(1) This makes hypothyroidism the most common disease arising from a hormonal insufficiency.(2) Gender is an influencing factor, as women are three to seven times more likely to develop hypothyroidism than men.(1) Known risk factors that increase the likelihood of developing this disease include having a family history of hypothyroidism and pregnancy.(1) Recent research by the British Medical Journal (2021) suggests that taking birth control pills, or oral contraceptives (OCs), may also increase the odds of developing hypothyroidism.(3)

Birth Control Pills Statistics

Oral contraceptives are a widely used form of birth control by women. Many individuals turn to these medications for reasons other than birth control such as relief from symptoms such as abnormal uterine bleeding, endometriosis, hormonal and menstrual irregularities, etc.(3)Approximately 6 million women in the US, aged 15-49, take oral contraceptives (OCs) each year.(4) The National Survey of Family Growth (2015-2017) reported that OCs are the second most common method of contraception used by women between the ages of 15-49.(4) The use of OCs is higher among younger populations and decreases with age. Approximately 90% of women taking birth control pills are < 40 years old and 54% are under the age of 20.(1)Therefore, an association between the use of OCs and the risk of hypothyroidism could potentially affect a significant number of individuals. These individuals, when presented with other options for contraception and/or better monitoring of thyroid function, may be able to avoid the increased risk of morbidity and mortality associated with hypothyroidism.

Birth Control Pills and Risk of Hypothyroidism

The British Medical Journey (2021) recently stated that women with a history of taking OCs for more than 10 years have greater odds of developing hypothyroidism (OR, 3.837; 95% CI 1.402-10.500; p=0.0090). Their finding was the result of a retrospective, cross-sectional study derived from information gathered in the National Health and Nutrition Examination Survey (NHANES) 2007-2012. This large epidemiological survey included a total of 30,442 participants. Of this number, 5116 females met the inclusion criteria for participation in the study. These individuals were divided into two groups: those with a history of OC usage (n=3034) and those that had never used OCs (n=2082).

Approximately 16% (830) of the combined individuals were identified as hypothyroid. Hypothyroidism was more frequently diagnosed in those with a history of taking OCs (17.7% vs 14.1%). The state of being hypothyroid was defined as either those taking levothyroxine, regardless of thyroid stimulating hormone (TSH) or those with a TSH >5.6 mIU/L.(3) Women should therefore consider the long-term health effects of OCs and the increased odds of developing hypothyroidism associated with their use.

This study had several strengths, including the large population surveyed, and the strict criteria used to control for confounders. Limitations were also inherent in this type of study. One of the main limitations is the lack of data to differentiate between the types of OCs used, including their chemical composition. Knowing the types of contraceptives used, i.e.: combined contraceptives containing estrogen and progestin versus progestin only contraceptives, may have provided different outcomes. Other limitations included possible recall bias due to the use of self-reported data from individuals, which can often be incorrect. These factors may have skewed the results obtained. It is also important to recognize a cross-sectional,