| Number Criteria |
| 1 Memory complaints (answer “yes” to question “do you have memory complaints”, or at least twice answering “sometimes” on the Strawbridge cognition scale26) |
| 2 Objective memory impairment (10 WLT27 delayed recall ⩽5 and percentage savings ⩽100) |
| 3 Normal general cognitive function (TICS28 ⩾19 and MMSE29 ⩾24) |
| 4 Intact daily functioning (no report of disability in activities of daily living on GARS-scale,30 except on the item “taking care of feet and toe nails”) |
| 5 Absence of dementia (TICS28 ⩾19 and MMSE29 ⩾24) |
| 6 Being able to perform moderate intensity physical activity without making use of walking devices—for example, a rollator or a walking frame |
| 7 Not using vitamin supplements/vitamin injections/drinks with folic acid, vitamins B-12 and B-6, comparable to the vitamin supplement given in the intervention |
| 8 Not suffering from epilepsy, multiple sclerosis, Parkinson’s disease, kidney disorder requiring haemodialysis, psychiatric impairment |
| 9 Not suffering from depression as measured by the GDS31 (cut off ⩽5) |
| 10 Not using medication for rheumatoid arthritis or psoriasis which interfered with the vitamin supplement |
| 11 No alcohol abuse (men <21 drinks a week, women <15 drinks a week) |
| 12 Not currently living in a nursing home or on a waiting list for a nursing home |
*Operationalisation of Petersen criteria for MCI (1–5) and additional inclusion criteria for the RCT (6–12).
GARS, Groningen activity restriction scale; GDS, geriatric depression scale; MCI, mild cognitive impairment; MMSE, mini mental state examination; RCT, randomised controlled trial; TICS, telephone interview for cognitive status; 10 WLT, 10 word learning test.