We have previously published an OE Original examining an updated guideline recommendation regarding the consumption of red meat (Red Meat - To eat or not to eat) which found that there was a very small or even trivial risk increase for the consumption of red meat on cardiovascular mortality, type 2 diabetes, and overall cancer mortality, although this was based on low- to very-low-certainty evidence.

However, new evidence has pointed to a potential benefit of the consumption of meat: its potential to reduce the risk of fracture. A recent prospective cohort study conducted by Oxford University (EPIC-Oxford) evaluating lifestyle characteristics of four diet groups in 65,000 men and women performed a sub-study regarding the impact of diet on fracture occurrence (Tong, 2020). In this OE original, we look at this study and other evidence which examines the impact of meat consumption on fracture risk.

Why was this study needed now?

The analysis performed by the EPIC-Oxford study is one of the first large, prospective studies to examine the role of meat consumption on fracture risk, with previous studies having smaller sample sizes of 210 and 8,570 patients each, respectively (Ho-Pham 2012; Dash 2012). There have been additional studies that are cross-sectional in nature, with two systematic reviews performed examining fracture risk in these cross-sectional trials (Iguacel 2018; Fabiani 2019). These systematic reviews found that vegans had an increased risk of fracture compared to meat eaters. However, these studies did not examine site-specific fracture rates.

The EPIC-Oxford study

The EPIC-Oxford study is a prospective cohort study of 65,000 men and women in the United Kingdom (UK), recruited between 1993 and 2001. The goal of the study was to determine the lifestyle characteristics of individuals who fall under 4 diet groups: meat eaters (any type of meat), fish eaters (fish is the only type of meat in the diet), vegetarians (do not eat meat or fish, but eat one or both of dairy or eggs), and vegans. The sub-study evaluating fracture risk examined health records of approximately 55,000 participants in 2016, for a follow-up range of 15-23 years since enrollment. Analysis was performed for all fractures, as well as site-specific fractures at the following locations: arm, wrist, hip, leg, ankle, and other main site fractures. Reasons/causes and severity of fractures were not reported. Individual socio-demographic, lifestyle and health characteristics were taken into the multivariable analysis.

What is the impact of meat consumption on fracture risk?

The results of the EPIC-Oxford study found that vegans have an increased risk of total, hip, and other main site fractures when compared to meat eaters (Table 1). Additionally, fish eaters and vegetarians had an increased risk of hip fractures when compared to meat eaters (Table 1).

Table 1: EPIC-Oxford significant results (only comparisons that showed a significant difference between groups).

What could be the reasons for increased fracture risk?

Two recent meta-analyses examining fracture risk have also evaluated bone mineral density in different diet groups (Iguacel 2018; Fabiani 2019). Fabiani 2019 found that patients with a healthy diet (characterized by high loading of vegetables and fruits with poultry, fish and grains) as well as diets high in milk and dairy resulted in a reduced risk of low-bone mineral density. Additionally, Iguacel, 2018 found that compared with omnivores, vegetarians and vegans showed a lower bone mineral density, specifically at the femoral neck and lumbar spine. This decreased bone mineral density, especially at the femoral neck, would leave persons practicing vegetarian or vegan diets susceptible to the elevated risk of fracture seen in the EPIC-Oxford study. It should be noted, however, that in Fabiani 2019, an analysis of a “Western/Meat” diet (consisting of high amounts of red meat, high fat, and high processed foods) resulted in a lower bone mineral density than the healthy diet, consisting mostly of fish and poultry. This could also be attributed to increased alcohol consumption and smoking in this group compared to the healthy and milk and dairy groups, which has been shown to be associated with low bone mineral density and osteoporosis (WHO 2007).

While diet demonstrates an impact on fracture risk and bone mineral density, the mechanisms for why this occurs are not well understood. It has been hypothesized that vegan diets result in a decreased intake of calcium, which may lead to increased fracture risk. However, a recent meta-analysis found that increases in dietary calcium, including from supplements, did not result in significant increases in bone mineral density (Bolland, 2015).  In line with this, the EPIC-Oxford study adjusted fracture risk for dietary calcium and still found the same significant risks, indicating that factors other than dietary calcium may be responsible for the increase in fracture risk.

Previous studies have also examined the role of dietary protein, with differing conclusions. Some studies have concluded that excessive protein intake leads to higher metabolic acid load, which can cause poor bone health due to increased bone resorption (Allen, 1979; Barzel, 1998). Other studies have indicated that high protein consumption can also relate to increased calcium absorption, which would indicate improved bone health (Kerstetter, 2003). As with calcium, when protein was used to adjust fracture risk in the EPIC-Oxford study, the same significant differences were seen.

While adjusting for these two factors did not change the results with respect to fracture risk, the EPIC-Oxford study indicated that calcium and protein were collected using self-reported questionnaires, which may have been subject to misreporting of information. There are additional factors which have been hypothesized to account for the increased fracture risk in vegan and vegetarian diets, but our understanding of these factors thus far remains inconclusive. These include a lower Body Mass Index (BMI) in vegan and vegetarians, lower levels of vitamin D and vitamin B₁₂.

The bottom line:

It is apparent in previous systematic reviews of observational studies as well as this large, prospective study that vegans are at an increased risk of fracture when compared to meat eaters, including increased risk of hip and lumbar spine fracture. Additionally, vegetarians and fish eaters also demonstrate an increased risk of hip fracture when compared to meat eaters. Previous research has found lower bone mineral density in non-meat eaters, although there have not been any causal reasons established for why this may be the case. Future research to determine the underlying mechanisms for why non-meat eaters are at increased risk of fracture is needed in order to help find ways to mitigate the potential fracture risk.

References

1. Tong TY, Appleby PN, Armstrong MEG, et al. Vegetarian and vegan diets and risks of total and site-specific fractures: results from the prospective EPIC-Oxford study. BMC Medicine. 2020;18(353):1-15.
2. Ho-Pham LT, Vu BQ, Lai TQ, et al. Vegetarianism, bone loss, fracture and vitamin D: a longitudinal study in Asian vegans and non-vegans. Eur J Clin Nutr. 2011;66(1):75-82.
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6. WHO Scientific Group on the Assessment of Osteoporosis at Primary Health Care Level. Summary Meeting Report. Geneva: World Health Organization. 2007. www.who.int/chp/topics/Osteoporosis.pdf
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9. Barzel US, Massey LK. Excess dietary protein can adversely affect bone. J Nutr. 1988;128(6):1051-3.
10. Kerstetter JE, O’Brien KO, Insogna KL. Dietary protein, calcium metabolism, and skeletal homeostasis revisited. Am J Clin Nutr. 2003;78(3 Suppl):584S-592S.