Abstract
BackgroundThe association between long-term metformin use and low vitamin B12 levels has been proven. However, the prevalence estimates of metformin-induced vitamin B12 deficiency showed considerable variation among the studies. The potential of the deficiency to cause or worsen peripheral neuropathy in type-2 diabetes mellitus (T2DM) patients has been investigated with conflicting results. The aim of the study was to investigate: 1) the prevalence of vitamin B12 deficiency in T2DM patients on metformin; 2) the association between vitamin B12 and peripheral neuropathy; 3) and the risk factors for vitamin B12 deficiency in these patients.MethodsIn this cross-sectional study, consecutive metformin-treated T2DM patients attending diabetes clinics of two public hospitals in South Africa were approached for participation. Participation included measuring vitamin B12 levels and assessing peripheral neuropathy using Neuropathy Total Symptom Score-6 (NTSS-6) questionnaire. The prevalence of vitamin B12 deficiency (defined by concentrations <150 pmol/L) was determined. Those with NTSS-6 scores >6 were considered to have peripheral neuropathy. The relationship between vitamin B12 and peripheral neuropathy was investigated when the two variables were in the binary and continuous forms. Multiple logistic regression was used to determine risk factors for vitamin B12 deficiency.ResultsAmong 121 participants, the prevalence of vitamin B12 deficiency was 28.1 %. There was no difference in presence of neuropathy between those with normal and deficient vitamin levels (36.8 % vs. 32.3 %, P = 0.209). Vitamin B12 levels and NTSS-6 scores were not correlated (Spearman’s rho =0.056, P = 0.54). HbA1c (mmol/mol) (OR = 0.97, 95 % CI: 0.95 to 0.99, P = 0.003) and black race (OR = 0.34, 95 % CI: 0.13 to 0.92, P = 0.033) were risk factors significantly associated with vitamin B12 deficiency. Metformin daily dose (gram) showed borderline significance (OR = 1.96, 95 % CI: 0.99 to 3.88, P = 0.053).ConclusionsClose to third of metformin-treated T2DM patients had vitamin B12 deficiency. The deficiency was not associated with peripheral neuropathy. Black race was a protective factor for vitamin B12 deficiency.
Highlights
The association between long-term metformin use and low vitamin B12 levels has been proven
As the first study to explore the topic in African populations, the aims of our study were to determine the prevalence of vitamin B12 deficiency in metformintreated type 2 diabetes mellitus (T2DM) patients, to investigate the relationship between vitamin B12 and peripheral neuropathy and to identify the risk factors for the vitamin deficiency in these patients
The questionnaire has been validated and was found suitable for evaluating peripheral neuropathy in clinical trials [19]. This is the first study to address the topic of metforminassociated vitamin B12 deficiency in African settings
Summary
The association between long-term metformin use and low vitamin B12 levels has been proven. Metformin is the cornerstone medication in the management of type 2 diabetes mellitus (T2DM) with estimates that it is routinely prescribed to 120 million patients with diabetes around the world [1]. Accumulating evidence from both observational and interventional studies has revealed the association between long-term use of metformin and vitamin B12 deficiency. Previous studies have shown that the prevalence of metformin-induced vitamin B12 deficiency varied greatly and ranged between 5.8 % and 52 % [3,4,5,6,7,8,9,10,11]. Such a wide range may be attributed to differences in cut-points chosen to define the deficiency, participants mean age, study settings, and metformin dose and duration of use
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