The uncertainty surrounding high intakes of
folic acid and associations with
cognitive decline in older adults with low
vitamin B12 status has been an obstacle to mandatory
folic acid fortification for many years. We estimated the prevalence of combinations of low/normal/high
vitamin B12 and
folate status and compared associations with global cognitive function using two approaches, of individuals in a population-based study of those aged ≥50 years in the Republic of Ireland. Cross-sectional data from 3781 men and women from Wave 1 of The Irish Longitudinal Study on Ageing were analysed. Global cognitive function was assessed by the Mini Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA). Prevalence estimates for combinations of
vitamin B12 (plasma
vitamin B12 < or ≥258 pmol/l) and
folate (plasma
folate ≤ or >45·3 nmol/l) concentrations were generated. Negative binomial regression models were used to investigate the associations of
vitamin B12 and
folate status with global cognitive function. Of the participants, 1·5 % (n 51) had low
vitamin B12 (<258 pmol/l) and high
folate (>45·3 nmol/l) status. Global cognitive performance was not significantly reduced in these individuals when compared with those with normal status for both
B-vitamins (n 2433). Those with normal
vitamin B12/high
folate status (7·6 %) had better cognitive performance (MMSE: incidence rate ratio (
IRR) 0·82, 95 % CI 0·68, 0·99; P = 0·043, MoCA:
IRR 0·89, 95 % CI 0·80, 0·99; P = 0·025). We demonstrated that high
folate status was not associated with lower cognitive scores in older adults with low
vitamin B12 status. These findings provide important safety information that could guide fortification policy recommendations in Europe.