Serum vitamin B12 concentration is associated with improved memory in older individuals with higher adherence to the Mediterranean diet

Background & aims: Vitamin B12 plays a crucial role in cognition, but its effect might be regulated by the presence of other micronutrients, such as folate. The aim was to evaluate the effects of vitamin B12 on cognitive performance according to adherence to the Mediterranean diet, and whether the Mediterra-nean diet also results in increased folate or vitamin B12 levels. Methods: This is a cohort study nested in a randomized controlled clinical trial performed in Hospital Clinic in Barcelona, Spain. A total of 170 participants of the PREDIMED trial (Barcelona -Hospital Clinic site) aged 55-80 years at high cardiovascular risk were included. Adherence to the Mediterranean diet was assessed using a validated 14-item questionnaire, memory function was evaluated with a battery of neuropsychological tests and serum vitamin B12 and folate were determined using an automated elec-trochemiluminiscence immunoassay system. Results: In the multivariable adjusted linear regression model, serum vitamin B12 concentration pre-sented a significant correlation with memory function (r2 = 0.57; P = 0.028) in participants with high adherence to the Mediterranean diet whereas the correlation was weak and inverse for those who presented a low adherence to the Mediterranean diet (r2 = 0.37, P = 0.731). Mediterranean diet adherence showed a positive association with serum folate, but not with serum vitamin B12. Conclusions: In an older Mediterranean population at high cardiovascular risk, changes in serum vitamin B12 correlate with better memory function only in the context of a high adherence to the Mediterranean pattern, suggesting that the effects of vitamin B12 goes further than a mere nutritional requirement. Institutional review board statement: The study was conducted according to the guidelines of the Declaration of Helsinki and was approved by the Institutional Review Board of the 11 participating centres. The study was registered with the International Standard Randomized Controlled Trial Number (ISRCTN) 35739639 (https://www.isrctn.com/ISRCTN35739639).(c) 2023 Published by Elsevier Ltd.