The study is designed as a double-blind randomised placebo-controlled trial. The procedures are illustrated schematically in Figure , and detailed in the text. The aim of this trial is to assess whether dietary supplementation with crystalline vitamin B12 will benefit electrophysiological indices of neurological function and cognitive function in older people with biochemical evidence of vitamin B12 deficiency in the absence of anaemia.
Flow chart of OPEN study protocol.
Approximately 10 National Health Service general practices, members of the Medical Research Council General Practice Research Framework (GPRF) or the Primary Care Research Network will be recruited. The practices will be situated in the South East of England to facilitate attendance at King's College Hospital. Community-dwelling individuals aged over 75 years of age will be identified from practice registers of participating general practices. The medical records of identified potential participants will be searched and those with pre-existing medically diagnosed diabetes and dementia will be excluded. Individuals with either Type 1 or Type II diabetes will be excluded because of their increased susceptibility for neuropathy that is unrelated to vitamin B12 deficiency. Individuals with pernicious anaemia will be excluded where vitamin B12 treatment is indicated. Individuals known to have alcohol addiction will be excluded, as will individuals with a history of epilepsy or who have implanted metallic devices such as pacemakers (for whom neurophysiological testing is contraindicated). In addition the list of potential participants will be checked by the named General Practitioner in the clinic who will use discretion to exclude individuals considered unsuitable to participate in the study (e.g. recent bereavement, terminal illness).
Potentially eligible individuals identified by this process will each receive a letter and information sheet from their general practice outlining the nature and relevance of the study. The invitation letter will also act as a screen for potential participants who are currently consuming vitamin B12 supplements (either singly or in combination with other vitamins and minerals) or have received a vitamin B12 injection in the last 6 months. Participants reporting the current daily use of vitamin B12 supplements or a vitamin B12 injection within the previous 6 months will be excluded from the trial. Potential participants will be invited to make an appointment with the research nurse at their local general practice. The invitation letter will explicitly state that if they do not wish to participate in the study it will not alter their health care in any way. Non-responders will be sent one reminder three weeks after the initial mailing.
On attending at their general practice, potential participants will be fully informed by the research nurse about the nature and relevance of the study and what will be involved if they agree to take part. The nurse will check with the patient that they do not have a pacemaker, are not epileptic, are not currently taking vitamin B12 supplements on a daily basis and have not had a vitamin B12 injection within the previous 6 months. Potentially eligible participants will be asked if they have been diagnosed with diabetes (confirmed by medical record check), and asked to have an assessment of cognitive function using the Mini Mental State Examination (MMSE) [14
]. Participants with an MMSE score of less than 24 (out of a maximum of 30) will be excluded. The cut-off of less than 24 has traditionally been used as a marker for possible dementia in adults. Those with an MMSE score of less than 24 will not be included further, will be thanked for their time and co-operation and will be asked if they wish to make an appointment with their General Practitioner to discuss their MMSE result.
Potential participants without a diagnosis of diabetes and with an MMSE score of 24 or greater will be asked to give full informed consent and to provide a blood sample and, if eligible, have their results and contact information passed to the OPEN study team. Participants providing informed consent will be asked to provide a 4.5 ml blood sample to assess serum vitamin B12 and haemoglobin concentrations.
Research nurses in the participating general practices will provide the results of the blood tests to all potential participants. Eligible individuals are defined as those with a low but not deficient vitamin B12 status who are not anaemic (serum vitamin B12 levels ≥ 107 pmol/l and <210 pmol/l - Beckman Coulter assay [15
] and haemoglobin levels ≥ 11 g/l for women and ≥ 12 g/l for men). Individuals found to have above average serum vitamin B12 status (≥ 210 pmol/l - Beckman Coulter assay) will be excluded from the study. Individuals found to have very low vitamin B12 levels (< 107 pmol/l - Beckman Coulter assay) or/and found to be anaemic (haemoglobin concentration <11 g/l for women and <12 g/l for men) will be referred to their General Practitioner for normal practice treatment and excluded from the study.
The contact details of eligible individuals will be passed to the OPEN study manager, who will make telephone contact with participants to restate the nature and relevance of the study and what will be involved if they agree to take part and to invite them to attend a baseline appointment at King's College Hospital. In addition, participants will be asked to complete a questionnaire on diet and psychological health at home and bring it with them to their baseline appointment. Transportation will be provided locally for the participant from their home to the hospital.
At the baseline visit, potential participants will be given the opportunity to discuss the study and ask any questions before being invited to give full informed consent to participate in the study. Individuals giving informed consent will be enrolled in the trial and shown how to contact the OPEN study manager and obtain more information from the study web-site [16
The OPEN study manger will telephone the central randomisation service to randomise the participant, giving identifying details and the participant's age. Randomisation will allow secure blind allocation of eligible participants to one or other arm of the study. Following random allocation a trial number will be given to each study participant. This will also be used to identify the supply of dietary supplements to be prescribed for each participant (see Dietary Intervention below). The study number will be entered on the participant's entry form. Pre-labelled identical-looking packs of dietary supplements will be stored at King's College Hospital. Minimisation criteria will be used to ensure a balance of key prognostic factors using the following two criteria: age group (75-79 and 80+ years) and gender. These two criteria have been selected as there are clear age and gender gradients in vitamin B12 status.
Participants will be asked to complete a questionnaire including a sequence of cognitive function tests, provide a blood sample, and undertake a series of neurophysiological function tests (see Baseline Data Collection below) which will in total take approximately 75 minutes to complete. Any couples recruited to the study will undertake their assessments separately.
The OPEN study has received ethics committee approvals from the National Research Ethics Service (08/H0305/18) and the London School of Hygiene & Tropical Medicine ethics committee (no. 5298). The OPEN study is registered on ISRCTN (54195799).