There is bad news for Type 2 diabetics. Their treatment with metformin can lead to deficiency of vitamin B12, which is also likely to get worse over time. Vitamin B12 is important for forming red blood cells and maintaining healthy neurological function.

Vitamin B12 is found in meat, dairy products, eggs, fish, shellfish and fortified breakfast cereals and symptoms of its deficiency can be fatigue, mental changes, and anemia and nerve damage known as neuropathy.

An estimated 246 million people around the world are diabetic and rates are expected to rise along with the number of people who are overweight or obese. Most sufferers have Type 2 diabetes, which happens mainly because of poor diet and lack of exercise.

Dutch scientists who carried out the study said the findings suggest that regular checking of vitamin B-12 levels during long-term metformin treatment should be "strongly considered" to try to prevent deficiency and its effects.

A research was conducted by Stehouwer’s team. A total of 390 people were followed, half the group took 850mg of metformin three times a day for 4.3 years on average, and the results were compared with the other half taking a dummy (placebo) drug showed that people who had taken metformin had a 19 percent reduction in their vitamin B12 levels compared with people who had taken a placebo or a dummy pill, who had almost no B12 change.

The results showed that it is reasonable to assume harm that will eventually occur in some patients with metformin-induced low vitamin B12 levels."