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19-12-2011 | Diabetes | Article

Metformin use linked to vitamin D deficiency in older diabetes patients


Free abstract

MedWire News: Metformin treatment is associated with vitamin B12 deficiency among individuals with Type 2 diabetes aged 50 years or older, report US researchers.

The findings suggest that neither the current daily recommended intake of vitamin B12 in people aged 50 and over (2.4 µg, according to the Institute of Medicine [IOM]), nor even the amount of vitamin B12 typically found in over-the-counter daily multivitamin supplements (6 µg), is sufficient to correct vitamin B12 deficiency in these patients, say Godfrey Oakley (Emory University, Atlanta) and colleagues.

The findings come from a comparison of data available for 1621 National Health and Nutrition Examination Survey participants with diabetes and 6867 participants without the condition.

The researchers report that the mean serum B12 concentration among diabetes patients who were taking metformin was 317.5 pmol/L, compared with 386.7 pmol/L in those who were not.

The age-, race-, and gender-adjusted prevalence of vitamin B12 deficiency (serum B12: ≤149 pmol/L) was 5.8% for those with Type 2 diabetes taking metformin, 2.2% for those with diabetes not taking metformin, and 3.3% for those without diabetes.

The corresponding rates of borderline deficiency (serum B12: >148 to ≤221 pmol/L) were 16.2%, 5.5%, and 8.8%.

Analysis showed that people without diabetes who used B12 supplements had an approximate 66.7% lower prevalence of both B12 deficiency (1.6 vs 4.8%) and borderline deficiency (5.5 vs 16.6%) than those who did not use B12 supplements.

In contrast, among those with Type 2 diabetes who were taking metformin, supplement use was not associated with a significant decrease in the prevalence of either B12 deficiency (5.3 vs 5.6%) or borderline deficiency (8.8 vs 15.5%) compared with no use.

However, when the patients were divided according to vitamin B12 dosage level (0, >0-6, >6-25, and >25 µg/day), the prevalence of B12 deficiency was 14.1% among those consuming 0-6 µg vitamin B12, compared with just 1.8% among those consuming more than 6 µg vitamin B12.

The researchers say their sample size was too small to determine which amount of vitamin B12 was associated with maximum protection, but that they did find a dose-response trend.

"Our results have public health and clinical implications by suggesting that neither 2.4 µg, the current IOM recommendation for daily B12 intake, nor 6 µg, the amount found in most multivitamins, is sufficient for those with Type 2 diabetes taking metformin," they say.

"The analysis suggests a need for further research," concludes the team in the journal Diabetes Care.

MedWire ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Sally Robertson