A study published in Neurology, the medical journal of the American Academy of Neurology, showed that older persons with hypothyroidism, commonly known as underactive thyroid, may be at an increased risk of acquiring dementia. People with thyroid conditions who needed to take thyroid hormone replacement therapy had a significantly higher incidence of dementia.

Insufficient thyroid hormone production by the thyroid gland results in hypothyroidism which may slow metabolism and included symptoms like fatigue, weight gain, and cold sensitivity. Hyperthyroidism might speed up metabolism and showed symptoms such as unintentional weight loss, an erratic or quick heartbeat, and jitteriness or anxiety.

The study analyzed the health records of 7,843 Taiwanese individuals with an average age of 75 years and who had been recently diagnosed with dementia. Researchers studied the history of hypothyroidism or hyperthyroidism. 133 participants were diagnosed with hyperthyroidism, while 102 individuals were affected with hypothyroidism. 

The researchers did not discover a connection between dementia and hyperthyroidism. They found that 0.9% of those with dementia had hypothyroidism, compared to 0.4% of those without dementia. Also, adults over the age of 65 with hypothyroidism were 80% more likely to develop dementia than those of the same age who did not have thyroid issues after adjusting for other factors that could impact the risk of dementia, such as sex, age, high blood pressure, and diabetes. A history of hypothyroidism was not linked to an increased incidence of dementia in those under 65.

Researchers found that those who solely took medicine for hypothyroidism had a threefold increased risk of dementia compared to those who did not. They concluded that thyroid conditions were linked to signs of dementia that may be treated to reverse them. However, further research is required to corroborate these conclusions. 

(Source: https://theprint.in/health/research-thyroid-problems-linked-to-increased-risk-of-dementia/1285645/)