A review of nine studies including 869 women and 1,880 men found that vegetarians had a four per cent lower bone mineral density (BMD) than omnivores, while the BMD of vegans was 6 per cent lower.
“The results suggest that vegetarian diets, particularly vegan diets, are associated with lower BMD, but the magnitude of the association is clinically insignificant,” wrote researchers based in Vietnam and Australia in the American Journal of Clinical Nutrition.
A growing market
A survey by the UK’s Food Standards Agency (FSA) found that 3 per cent of respondents described themselves as ‘completely vegetarian’, with an additional 5 per cent ‘partly vegetarian’.
These increases have resulted in growing sales of meat-free foods. According to a report by Mintel last year the total meat-free foods market in the UK was estimated to be worth £739 million (€787 million), with meat substitutes reportedly accounting for ₤170 million (€181 million).
Previous studies have reported inconsistent results for meat-free diets and bone health however, and with the World Health Organisation calling osteoporosis its biggest global healthcare problem, understanding how the dietary pattern may affect bone health is of utmost concern.
An estimated 75 million people suffer from osteoporosis in Europe, the USA and Japan.
Important review
In an accompanying editorial, Susan Lanham-New from the Faculty of Health and Medical Sciences at the University of Surrey, UK described the new meta-analysis as “a most timely and important piece of work”.
“That said, this study does not provide the ‘conclusive’ evidence that pubic health specialists require,” she added, before noting: “The numbers of subjects are relatively small given the number of vegetarians worldwide; the study design of all but one of the studies is cross-sectional rather than longitudinal/prospective; and although the quality of the studies selected is in one way a strength, this meta-analysis is not fully representative of the many studies published in this area.”
Despite such caveats, Lanham-New stated that it could be “concluded that vegetarianism is not a serious risk factor for osteoporotic fracture”.
In addition to reductions of BMD in vegetarians and vegans, the Vietnam- and Australia-based researchers noted that the probability of vegetarians having reduced bone strength at the hip bone or in spine was 42 and 32 per cent, respectively.
Mechanism
Commenting on observations, Lanham-New said that the vegetarian diet is hugely complex, and that vegetarianism is often not only about differences in the nutrient components of the diet, but also in lifestyle factors.
“Historically, the fundamental theories linking vegetarianism to the skeleton were focused on there being a link between acid-base homeostasis and the skeleton and on the assumption that the long-term ingestion of a vegetable-based diet would provide an alkali (ash) and hence be beneficial to bone health,” she explained.
“Future research should focus attention on whether there are any particular components of a vegetarian/vegan diet (eg, higher intake of fruit and vegetables) that would yield specific benefits to the skeleton, including the determination of the specific concentrations that would be required for optimum bone health, and what are the underlying mechanisms that affect overall bone health,” she concluded.
Source: American Journal of Clinical Nutrition
October 2009, Volume 90, Number 4
“Effect of vegetarian diets on bone mineral density: a Bayesian meta-analysis” (pages 943-950)
Authors: L.T. Ho-Pham, N.D. Nguyen, T.V. Nguyen
“Is ‘vegetarianism’ a serious risk factor for osteoporotic fracture?” (pages 910-911)
Author: S.A. Lanham-New