Serum transthyretin level and its relationship with cognitive function in community-dwelling older people: Cross sectional and longitudinal study

•Serum TTR was associated with cognitive scores in normal cognitive function group.•Those with higher blood TTR levels had higher risk of mild cognitive impairment.•Serum TTR levels might be a useful marker for cognitive function in preclinical AD. Serum transthyretin (TTR) level has suggested association with mild cognitive impairment (MCI) and dementia. To clarify its usefulness as a biomarker of change in cognitive function in older individuals with normal cognitive function (NC) as a phenotype, we investigated the relationship between cognitive scores and TTR levels. We also investigated the involvement of TTR in the transition from NC to MCI. Cognitive function was evaluated using Addenbrooke's Cognitive Examination-Revised (ACE-R). A cross-sectional study was conducted in community-dwelling older people (n = 211) with NC, MCI, or dementia according to ACE-R scores. A 32-month longitudinal study was then conducted (n = 29). Mean TTR levels did not differ between the NC, MCI and dementia groups. Linear regression analysis showed a significant relationship in people with NC between TTR and ACE-R (β = -0.192; p < 0.001). Multiple regression analysis adjusted for stepwise procedure-selected covariates showed that TTR was significantly associated with ACE-R in people with NC (β = -0.130; p = 0.014). Furthermore, multiple regression analysis showed significant association between TTR level and memory (β = -0.584; p = 0.002) and with language (β = -0.743; p = 0.031) in people with NC. In the longitudinal study, mean TTR level at baseline in women with MCI was significantly higher than that in women with NC (p = 0.044). Serum TTR level is suggested to be associated with cognitive scores in people with NC and to be an indicator of progression from NC to MCI.