Insulin resistance is a condition similar to type 2 diabetes mellitus, or T2DM. This condition also causes the increase of glucose levels in your blood and increases the risk for cardiovascular diseases. Elevated glucose levels can be modified by lifestyle changes. If that is not sufficient, you may be treated with glucose-lowering drugs, such as metformin. However, most drugs have at least some side effects. In the case of metformin, the long-term use causes vitamin B-12 deficiency that affects mainly your nerves and red blood cells.
Insulin Resistance
Glucose in your food is absorbed via the intestines into your blood. Cells of your body need glucose as a source of energy. Glucose can enter the cells in the presence of insulin. When your cells become less sensitive to insulin, the transit of glucose from blood into cells becomes less efficient. You then feel tired despite having high glucose levels in your blood. Insulin resistance can be evaluated by measuring your glucose levels after overnight fasting. The levels should then be less than 100 mg/dl of blood. When your glucose levels are between 100 and 125 mg/dl, your cells are resistant to insulin. When the levels reach 125 mg/dl or more, the condition is more severe and you are diagnosed with T2DM. The current drug of choice for lowering your blood glucose is metformin.
Metformin
Diabetes Prevention Program Research Group assessed the effects of metformin on patients with insulin resistance in a study published in February 2002 issue of "New England Journal of Medicine." The researchers compared the incidence of T2DM in patients who received no drug, were treated with metformin or who exercised at least 150 minutes per week. Results of the study indicate that exercise reduces the incidence by 58 percent and the treatment with metformin by 31 percent, as compared to the untreated group.
Vitamin B-12 Deficiency
Long-term use of metformin, however, may reduce the levels of vitamin B-12 in your body, according to Jolien de Jager and colleagues in the May 2010 issue of the "British Medical Journal." This is due to decreased absorption of vitamin B-12 from the intestine. The deficiency can manifest as tingling and numbness in your hands and feet, which is referred to as peripheral neuropathy, with "glove-stocking" distribution. Vitamin B-12 is also important for maintaining your numbers of red blood cells. When vitamin B-12 levels decrease, you may feel fatigued and have shortness of breath, particularly during exercise.
Prevention
The research data indicate that only a subgroup of metformin-treated patients develops the vitamin B-12 deficiency. When you are treated with metformin for long, your levels of vitamin B-12 should be regularly checked. To reduce the possibility of developing the deficiency, it is useful to eat food that is rich in vitamin B-12, such as sea food, meat, chicken breast, milk or eggs. For vegetarians, cereals fortified with the vitamin B-12 can be an alternative source.
References
- "Physiological Basis of Medical Practice"; John B. West, M.D., Ph.D., D.Sc.; 1990
- "Diabetes Care"; American Diabetes Association Standards of Medical Care in Diabetes 2011; January 2011
- "New England Journal of Medicine"; Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin; Knowler W.C. et al.; February 2002
- "British Medical Journal"; Long-term Treatment with Metformin in Patients with Type 2 Diabetes and Risk of Vitamin B-12 Deficiency: Randomised Placebo Controlled Trial; de Jager J. et al.; May 2010
- National Institutes of Health Office of Dietary Supplements: Vitamin B-12
