Screening for subclinical thyroid dysfunction does not appear to be useful in the prevention of cognitive decline or dementia, Australian research shows.
Findings from a study published in JAMA Internal Medicine suggest existing clinical guidelines that recommend screening of subclinical thyroid dysfunction for prevention of cognitive decline or dementia should be revisited.
The study comprised an analysis of individual participant data from more than 74,000 adults across 23 cohorts investigating thyroid function and cognitive function and/or dementia.
At baseline, 80% of participants were euthyroid, 0.8% overtly hyperthyroid, 3.4% subclinically hyperthyroid, 5.6% subclinically hypothyroid, and 0.9% overtly hypothyroid.
Median follow-up ranged from 3.8 to 15.3 years, accumulating 525,222 person-years.
The study found thyroid dysfunction was not associated with global cognitive function or annual change in global cognitive function during follow-up.
“Participants with overt hypothyroidism had 0.11 standardised mean difference (95% CI, −0.01 to 0.23; P = .09) higher decline per year in global cognitive function than participants who were euthyroid, which translates to approximately 0.1 point on the MMSE scale faster decline per year based on the SD in the largest cohort for this analysis,” the study authors said.
The study found no association between continuous FT4 levels and global cognitive function.
It also found participants with overt hyperthyroidism had 0.20 standardised mean difference (95% CI, 0.07 to 0.33; P = .002) higher executive function score compared with participants who were euthyroid, but the association disappeared when participants using thyroid medication were removed.