Vegans At Greater Risk of Fracture?

About a month ago a worrying study was published by researchers working on the EPIC-Oxford Study. They looked into the differences in fracture risk between meat eaters, vegetarians and vegans. It was done by following a group of around 55,000 men and women for an average of 17 years. It should be said that most fractures are generally due to poor bone health leading to decreased bone mineral density (BMD) and eventually osteoporosis.

The authors note that previous studies have shown that vegetarians (and vegans) have lower BMD than non-vegetarians but that the associated fracture risk is unclear. The combination of vitamin D and calcium has been found to be effective in decreasing fracture risk. Studies have also linked protein intake to bone health. High protein intake increases intestinal calcium absorption and stimulates the production of insulin-like growth factor (IGF-1) which is associated with better bone health. And finally, body mass index (BMI) could also play a part in fracture risk. The lower BMD found in US vegetarians may be explained by their lower BMI.

Tong et al. summarise their findings as follows:

 “The higher observed risks of fractures in non-meat eaters were usually stronger before BMI adjustment, which suggests that the risk differences were likely partially due to differences in BMI. Vegetarians and vegans generally have lower BMI than meat eaters, and previous studies have reported an inverse association between BMI and some fractures, particularly hip fractures, possibly due to reasons including the cushioning against impact force during a fall, enhanced oestrogen production with increased adiposity, or stronger bones from increased weight-bearing.”

“Although a statistically significant higher risk of total and hip fractures was only observed in vegans in the lower BMI category (<?22.5?kg/m²), our interpretation is limited by the small numbers of cases in each stratum in these analyses, especially because of the strong correlation between diet group and BMI, which results in very few vegans in the higher BMI category, and vice versa comparatively small numbers of meat eaters with a low BMI.”

“In this study and previous studies, vegans had substantially lower intakes of calcium than other diet groups since they do not consume dairy, a major source of dietary calcium, while both vegetarians and vegans had lower protein intakes on average. In the human body, 99% of calcium is present in bones and teeth in the form of hydroxyapatite, which in cases of calcium deficiency gets resorbed to maintain the metabolic calcium balance, and thus, osteoporosis could occur if the calcium was not restored.”

“Overall, vegans in this study had higher risks of total and some site-specific fractures (hip, leg, vertebra) than meat eaters. The strongest associations were observed for hip fractures, for which fish eaters, vegetarians, and vegans all had higher risks. These risk differences might be partially explained by the lower average BMI, and lower average intakes of calcium and protein in the non-meat eaters. However, because the differences remained, especially in vegans, after accounting for these factors, other unaccounted for factors may be important.”

We have known for some time that astronauts suffer from bone loss whilst in space. This is partly due to the effect of weightlessness and reduced physical activity leading to decreased bone compressive forces. Bone compressive forces help increase BMD and create stronger bones. As vegans usually have lower BMIs, their bones are subject to smaller compressive forces than meat-eaters. This can be overcome by resistance exercise and weight lifting. And of course, it is particularly important for those eating a plant-based diet to ensure they get an adequate intake of vitamin D, calcium and protein to maintain bone health.