Thyroid problems in older people may be linked to an increased risk of dementia, new research suggests.

According to the study, older people with hypothyroidism – also called underactive thyroid – could have higher chances of developing the condition.

Hypothyroidism occurs when the thyroid gland does not make enough thyroid hormones.

This can slow metabolism, and symptoms include feeling tired, weight gain and sensitivity to cold.

Study author Chien-Hsiang Weng, of Brown University in America, said: “In some cases, thyroid disorders have been associated with dementia symptoms that can be reversible with treatment.

“While more studies are needed to confirm these findings, people should be aware of thyroid problems as a possible risk factor for dementia and therapies that could prevent or slow irreversible cognitive decline.”

Researchers analysed the health records of 7,843 people newly diagnosed with dementia in Taiwan and compared them to the same number of people who did not have dementia.

The scientists looked to see who had a history of either hypothyroidism or hyperthyroidism – overactive thyroid, when the thyroid produces too much hormone, potentially leading to increased metabolism and symptoms including unintended weight loss, rapid or irregular heartbeat.

A total of 102 people had hypothyroidism and 133 had hyperthyroidism, and no link was found between hyperthyroidism and dementia.

Of the people with dementia, 68, or 0.9%, had hypothyroidism, compared to 34 of the people without dementia, or 0.4%.

After adjusting for other factors which could affect the risk of dementia – such as sex, age, high blood pressure and diabetes – researchers found that people over age 65 with hypothyroidism were 80% more likely to develop dementia than people the same age who did not have thyroid problems.

For those younger than 65, having a history of hypothyroidism was not associated with an increased risk of the condition.

People who took medication for hypothyroidism were three times more likely to develop dementia than those who did not take medication, the study found.

Dr Weng said: “One explanation for this could be that these people are more likely to experience greater symptoms from hypothyroidism where treatment was needed.”

The findings are published in the Neurology journal.

Dr Sara Imarisio, head of research at Alzheimer’s Research UK, said: “The study did not look at the reasons for this high correlation and future studies should investigate this further.

“If you are worried about your thyroid, it is best to arrange an appointment with your doctor who can do some simple tests to check that it is working properly.

“You can also see information and support on the British Thyroid Foundation website for people affected by thyroid problems.

“This study highlights an important area of future research as in the UK two in 100 people have an underactive thyroid, so this increased risk needs to be better understood.”