Metformin use associated with Vitamin B12 deficiency in elderly

Vitamin B12 deficiency is common among institutionalized elderly using metformin, finds a new retrospective study in the Archives of Gerontology and Geriatrics.

Elderly people living in long-term care institutions are particularly at risk of vitamin B₁₂ deficiency. The prevalence of vitamin B₁₂ deficiency was 34.9% among the 1996 institutionalized elderly residents in a previous study. Wong Chit Wai, Department of Medicine and Geriatrics, Caritas Medical Centre, Hong Kong, China, and colleagues conducted the study to evaluate the association of metformin use with vitamin B₁₂ deficiency in the same group of patients.

The study holds importance as metformin can cause vitamin B12 malabsorption, which can be reversed with calcium supplementation. And also, uncorrected vitamin B12 deficiency is associated with cognitive impairment, depression, and permanent nerve damage.

For the study, the research team analyzed 1996 long-term care center residents aged ≥65 years not receiving B12/folate supplements at the time of serum vitamin B12 measurement, including 25.4% with diabetes and 188 receiving metformin.

• Mean serum vitamin B12 level:
  
  
  
  • 184 pmol/L among those with diabetes taking metformin
  
  
  • 243 pmol/L among those with diabetes not taking metformin
  
  
  • 229 pmol/L among those without diabetes
  
  
  
  


• The prevalence of vitamin B₁₂ deficiency in diabetic patients taking metformin was 53.2% compared with 31% of diabetic patients not taking metformin and 33.3% of those without diabetes.


• Among the vitamin B₁₂ deficient patients, diabetic patients taking metformin had lower serum vitamin B₁₂ concentration (97 pmol/L) than the diabetic patients not taking metformin (113 pmol/L) and those without diabetes (111 pmol/L).


• Subanalysis of 174 metformin users found that the dose and duration of metformin use were significantly associated with vitamin B₁₂ deficiency.


• Adjusted odds ratio for those taking metformin ≥1500 mg /day was 2.72 (95% CI 1.11–6.7, P = 0.029) compared with those using metformin <1000mg/day.


• The adjusted odds ratio for those taking metformin>4 years was 3.00 (95% CI 1.35–6.68, P = 0.007) compared with those taking metformin <2 years.


• Prevalence of vitamin B₁₂ deficiency among those taking metformin ≥1500 mg/day for >2 years was 75.9% and was more than 2 times that of patients taking metformin <1500 mg/day for ≤2 years (35.3%).

"Metformin use is associated with increased risk and severity of vitamin B₁₂deficiency in the institutionalized elderly residents. Patients taking metformin ≥1500 mg/day for >2 years are, particularly at risk. Testing for vitamin B₁₂ status before and regularly after the start of metformin may be considered," concluded the authors.