Metformin and B12 deficiency

I found the following at Wikipedia:

Long-term use of metformin has been associated with increased homocysteine levels and malabsorption of vitamin B12. Higher doses and prolonged use are associated with increased incidence of B12 deficiency, and some researchers recommend screening or prevention strategies. 

Here is link with great info:

Metformin & B12 

Found another article:

Researchers at the University of Pittsburgh  in their second report describes vitamin B12 deficiency in patients with type 2 diabetes who take metformin. It is estimated that 10 to 30 percent of patients taking metformin develop vitamin B12 deficiency.

In people taking metformin who have a reasonable dietary intake of the vitamin, the deficiency can take 10 to 15 years to develop. It is not known how metformin causes the deficiency, but it may be related to changes in absorption of the vitamin.

This report urges doctors to look for signs and symptoms of B12 deficiency in their patients taking metformin. These include fatigue, weakness, nausea, constipation, flatulence, loss of appetite or weight loss. Neurolgic changes such as numbness and tingling in the hands and feet may also signal B12 deficiency.

I also read about a study done by Dr K.P.Singh and others on Osteoporosis and vitamin B12 deficiency among metformin users which was presented in IBMS 2009 at Sydney.This is quite interesting to note that vegetarians have significantly low Vitamin B12 levels in their blood. I am keen to know about mechanism of OSTEOPOROSIS AMONG METFORMIN USERS.