European Journal of Nutrition

, Volume 50, Issue 2, pp 97–106 | Cite as

Is a low blood level of vitamin B12 a cardiovascular and diabetes risk factor? A systematic review of cohort studies

  • Snorri B. Rafnsson
  • Ponnusamy Saravanan
  • Raj S. Bhopal
  • Chittaranjan S. Yajnik
Original Contribution

Abstract

Purpose

To assess the prior hypothesis that low blood vitamin B12, partly through hyperhomocysteinemia and partly through direct effects, increases the risk of cardiovascular diseases and diabetes. As background, we also extracted all-cause mortality from the studies that met our criteria.

Methods

A systematic review of prospective cohort studies identified through searching six electronic databases, screening of reference lists, and citation search. Included studies reported data on the association between vitamin B12 blood levels, or other appropriate surrogate biological markers e.g. holotranscobalamin or serum/urine methylmalonic acid, and fatal or non-fatal incident diabetes and cardiovascular events.

Results

Seven studies were included. Studies differed regarding the population studied, length of follow-up, study outcomes, and data analysis—a narrative synthesis approach was performed to examine the results. Most studies met few of the quality assessment criteria which were adapted from the Scottish Intercollegiate Guidelines Network (SIGN). Only one high-quality study reported that low B12 increased the risk of incident cerebral ischaemia (RR = 1.76; 95% CI = 1.16–2.68). After controlling for homocysteine, the association persisted although weakened (RR = 1.57; 95% CI = 1.02–2.43), suggesting that the effects of low B12 were only partly mediated by homocysteine. In two studies, higher B12 levels were associated with a greater risk of total mortality (RR = 1.00; 95% CI = 1.00–1.00 and HR = 1.15; 95% CI = 1.08–1.22, respectively) and combined fatal and non-fatal coronary events (RR = 1.00; 95% CI = 1.00–1.00). No association between study outcomes and vitamin B12 levels was found in four other studies.

Conclusions

Surprisingly, there is only very limited evidence that vitamin B12 deficiency predisposes to the risk of mortality and morbidity from either cardiovascular diseases or diabetes in adults. Current data do not support vitamin B12 supplementation to reduce the risk of cardiovascular diseases or diabetes.

Keywords

Vitamin B12 Cardiovascular diseases Diabetes mellitus type 2 Cohort studies Aetiology 

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Snorri B. Rafnsson
    • 1
  • Ponnusamy Saravanan
    • 2
  • Raj S. Bhopal
    • 1
  • Chittaranjan S. Yajnik
    • 3
  1. 1.Public Health Sciences Section, School of Clinical Sciences and Community Health and Centre for Population Health SciencesUniversity of EdinburghEdinburghScotland, UK
  2. 2.Clinical Sciences Research Institute, Warwick Medical SchoolCSB, UHCW NHS TrustCoventryUK
  3. 3.Diabetes UnitKEM Hospital and Research CentrePuneIndia

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