Outcomes
We had two primary outcomes:A standardised 10-min subtest of Raven Advanced Progressive Matrices (RAPM) [The Wechsler auditory Backward Digit Span (BDS) [RAPM is a test of abstract reasoning. Each item in the test consists of a 3 × 3 matrix with pictures of geometric forms. One of the pictures is missing and the task consists of choosing the right picture to fill this gap out of eight alternatives. The full RAPM consists of 80 items and has a time limit of 40 min. We used the same standardised 10-min subtests of the RAPM as Rae et al. [The Backward Digit Span is a test of working memory. The tester reads increasingly longer series of digits to the participant whose task it is to remember and repeat them in reverse order. The task starts with two digits. Each length has two series of digits. The test ends after wrong answers to two series of the same length. The BDS score consists of the sum of correct responses.We had eight further exploratory outcomes:The D2 Test of Attention [The Trail-Making-Test A (TMT-A), a test of visual attention [The Trail-Making-Test B (TMT-B), a test of task switching [The Block-Tapping-Test, a test of visuospatial working memory [The Auditory Verbal Learning Test (AVLT, in German: VLMT), a word-learning test including immediate recall, delayed recall, and recognition [The Brief-Visuospatial-Memory Test—Revised (BVMT-R), a test of visuospatial memory [The Stroop test (in German: Farb-Wort-Interferenz Test, a test of inhibitory control [Regensburger Wortflüssigkeitstest, a test of verbal fluency [Participants reported side effects experienced during the supplementation period in a free text form on the day of testing. How side effects would be grouped for the report was determined after evaluating all entries. At baseline testing, participants performed a test of crystallised intelligence called “Mehrfachwahl-Wortschatztest (MWT-B)” [