A recently published study (November 22nd, 2020) of participants in the large EPIC-Oxford prospective cohort study, the bone fracture rate was analyzed in over 29,000 meat eaters, 8,000 fish eaters, 15,000 vegetarians and 1,900 vegans. While it is known that vegans have lower body mass (BMI) and lower bone mineral density (BMD), this study, the largest study of its kind to look at bone fractures in different dietary groups, found that vegans were more likely to get bone fractures than vegetarians and much more likely than meat eaters. How much is 'much more'? Compared with meat eaters, vegetarians had 4 times as many fractures and vegans had 19.4 times more fractures. This rate was calculated per 1000 people over a 10 year period and the average length of time these participants were followed was 17.3 years.

The authors of the study attribute the higher risk to the low intake of protein and calcium (mostly from dairy products) as well as lower body mass, but recognize that other nutritional factors like vitamins D and B12 likely play a role. Vegans are particularly at risk for B12 deficiency and even though the literature is mixed, it is generally accepted that low B12 levels can play a role  directly in reducing osteoblastic (bone formation) activity. B12 deficiency can also have an indirect effect by raising homocysteine and methylmalonic acid (MMA) levels which have been shown in in-vitro experiments to stimulate osteoclastic (bone resorption) effects - thereby contributing to lower bone density.

Regardless of the mechanism, a meta-analysis of four prospective studies including nearly 7,500 subjects showed a 4% decrease in fracture risk for every 50 pmol/L increase in serum vitamin B12 levels [if below normal] and a meta-analysis of eight studies of over 11,500 subjects demonstrated an increase in fracture risk of 4%  for every 1 umol/L rise in homocysteine levels (indicating lower B12, B6, folate or choline).