A Dose-finding Randomized Trial of Vitamin B12 Supplementation: Biomarker Responses and Implications for Dietary Recommendations.

Detailed Description:

The aim of this study is to investigate the response of recognized vitamin B12 biomarkers (serum total vitamin B12; serum holotranscobalamin; plasma methylmalonic acid; plasma homocysteine) to intervention with supplemental vitamin B12 at doses within and beyond the range of typical dietary intakes in younger and older adults.

The sample size will be estimated by using typical variances from published studies on plasma homocysteine responses to vitamin B12 supplementation in adults. The calculations are based on changes in plasma homocysteine, as it is considered a functional indicator of vitamin B12 status. The typical standard deviation of change will be set at 2µmol/L (Clarke et al. 1998; McKinley et al. 2002) with the minimal detectable difference being 1.5µmol/L at 80% power and a significance level of 5%. Calculations determined that 40 subjects would be required for each of the three treatment groups plus placebo in order to show significant differences in plasma homocysteine concentrations.

Participants will be recruited by posters, advertisement, emails and organized meetings to promote the study among staff and students at Ulster University, Coleraine, workplaces, social and sporting clubs and sheltered accommodation for older adults in the surrounding local community. Those interested in the study will receive a participant information sheet and further details about the study. A signed informed consent will be obtained from all who are willing to participate in the study. A screening questionnaire and a non-fasting blood sample will be taken to identify those eligible to take part in the study. Exclusion criteria will be: history of gastrointestinal, hepatic, renal, vascular or haematological diseases or diabetes; those taking medications that interfere with folate or vitamin B12 metabolism (e.g. methotrexate, proton pump inhibitor drugs); use of B vitamin supplements; pregnancy; plasma creatinine concentration > 130 µmol/L; those with hypochlorhydria (diagnosed serologically by pepsinogen I to Pepsinogen II ratio < 3); those individuals with the 677C→T polymorphism in the MTHFR gene and those aged 60 years and over who scored <25 on Folstein's Mini-Mental State Examination (a cognitive function screening test).

All eligible participants will undergo a pre-treatment phase with 400 µg/day folic acid (FA) for 11 weeks; the treatment with FA will continue until the end of the trial. At the end of the pre-treatment phase, participants will provide a non-fasting blood sample (baseline sample) and will be stratified within each age category (<60 years and ≥60 years) according to their homocysteine concentrations and subsequently randomized in a 1:1:1:1 allocation ratio to one of the four treatments for 16 weeks: 400 µg/day FA + placebo, 400 µg/day FA + 2 µg/day vitamin B12, 400 µg/day FA + 10 µg/day vitamin B12 or 400 µg/day FA + 50 µg/day vitamin B12. A non-fasting blood sample will be collected at the end of the intervention. Blood samples at baseline and post-intervention will be analyzed for biomarkers of folate and vitamin B12 status. In order to encourage maximal compliance, participants will be contacted regularly and provided with supplements in 7-day pillboxes every 4 weeks during the pre-treatment phase and the intervention, and will be asked to return the used pillboxes; the number of unused capsules will be recorded to monitor compliance. The intervention will be conducted on a staggered basis and both study participants and researchers will be blind to treatment allocations. Dietary intake of participants will be assessed using a four-day food diary (based on 2 weekday and 2 weekend day intakes) and a food frequency questionnaire regarding specific intake of foods fortified with vitamin B12 and FA.