Thyroid disorders are among the most common endocrine diseases, with a particularly high prevalence in many provinces of the country, especially Yazd City, Iran. In a recent population-based study conducted on the adult population of Yazd City, it was found that approximately 19% of the people in Yazd City have hypothyroidism and 4.5% have hyperthyroidism. The findings showed that 60% of all cases were observed in women, with the highest prevalence in the 40 to 60-year age group. This pattern is consistent with global evidence indicating a higher incidence of thyroid disorders among middle-aged and elderly women.
One of the noteworthy findings of this study was the role of consuming tea with rock candy (chay-e nabat) and other sweetened beverages in increasing the risk of hypothyroidism. According to the analyses, regular consumption of these drinks raises the likelihood of developing hypothyroidism by approximately 3.5 times. This result aligns with several international studies that have linked high sugar intake to systemic inflammation and hormonal alterations. Increased glycemic load and overstimulation of the pancreas and the hypothalamic–pituitary axis may negatively affect thyroid function.
On the other hand, not using iodized salt was identified as one of the most important preventable risk factors. In recent years, the use of rock salt, mountain salt, and sea salt has increased due to non-scientific advertising, even though many of these salts lack adequate iodine. The findings of the present study show that not consuming iodized salt doubles the risk of hypothyroidism. This observation is fully consistent with the World Health Organization’s report stating that iodine deficiency is the most common preventable cause of hypothyroidism worldwide.
In addition, insufficient sleep and poor sleep quality were associated with a 13% increase in the likelihood of hypothyroidism in this study. Research has shown that sleep disturbances can affect the hypothalamic–pituitary–thyroid axis, disrupt hormonal regulation, and potentially lead to hypothyroidism.
Hypothyroidism may be accompanied by symptoms such as depression, reduced energy and vitality, sleep disturbances, weight gain, dry skin, and cognitive changes. Given the high prevalence of this condition in Yazd City, public awareness of risk factors and preventive behaviors is highly important.
Simple lifestyle modifications—such as consistent use of iodized salt, reducing the consumption of sweetened beverages, and improving sleep quality—can play a meaningful role in lowering the incidence of hypothyroidism. It is hoped that enhancing education and increasing public awareness, especially among women and middle‑aged individuals, will facilitate better prevention and management of this disorder.
The samples consisted of 10,000 residents of Yazd City aged 20 to 70 years, who were selected randomly based on postal codes. These individuals have been monitored and screened annually over a 12‑year period. Biological samples—including hair and nails, urine, saliva, and blood—from approximately 7,000 of these participants are stored in the university’s bio-bank. The name of this bio-bank is Yazd Biobank (ZIBA).