While not eating meat is a popular dietary choice and may offer several health benefits, researchers are still seeking to understand the potential risks of following a vegetarian diet, with a recent UK study suggesting that this might raise the risk of hip fractures for both men and women.
The researchers said this was possibly partly related to the lower body mass index among participants on a vegetarian diet – the team had examined the risk not just among vegetarians, but among meat-eaters and pescatarians as well, reports MedicalNewsToday.
The study is published in BMC Medicine.
The prospective cohort study included more than 400 000 participants, and data from the UK Biobank, which includes individuals from England, Scotland and Wales aged 40-69.
The team looked at the risk for hip fractures and followed up with participants an average of 12.5 years later. They excluded people based on specific criteria, including if they had a previous hip fracture or osteoporosis history.
Based on food frequency questionnaires, researchers divided participants into four key groups:
• Regular meat-eaters – participants who reported eating meat five or more times weekly.
• Occasional meat-eaters – who ate meat less than five times a week.
• Pescatarians – who ate fish but otherwise did not eat meat.
• Vegetarians – all ate no meat, but the group included those who ate dairy or eggs and those who did not eat eggs or dairy (vegans).
Researchers chose to combine the vegan and vegetarian groups because only a few participants were vegan.
The study accounted for many confounders, including the participants’ sex, ethnicity, regular use of nutritional supplements, activity level, smoking status, and alcohol consumption. They then looked at the associated risk for hip fractures among these different nutrition groups.
The findings indicated that people who followed a vegetarian diet were at a 50% higher risk of experiencing a hip fracture compared with meat-eater groups and pescatarians.
Why the higher fracture risk?
Researchers noted that some of this heightened risk might be explained by the lower BMI of participants who followed a vegetarian diet. The authors speculated that a lower BMI could mean poor health of muscles and bones or reduced cushioning from impact forces during a fall, from lack of fat.
But most of the reasons for the risk association were unclear. The authors speculate the increased hip fracture risk could be related to lower levels of protein and other key nutrients among vegetarians.
Dr Emily Leeming, a registered dietitian and nutrition scientist, who was not involved in the study, said: “We know that being at a slightly higher BMI is protective against risk of fractures from other studies, so this could be partially explained by differences in bone mass density. In this study, people who ate a vegetarian diet had, on average, a lower BMI than the other diet groups. However, as the study shows, there are possibly other factors at play too.
“The vegetarian participants were less likely to reach their protein intake requirements than the other groups, with adequate protein intake essential for building and maintaining bone mass. This may also be exacerbated by poor intakes of other nutrients involved in bone health.”
James Webster, first study author, told MedicalNewsToday: “We found that vegetarians were at a 50% greater risk of hip fracture than regular meat-eaters, regardless of sex. Lower BMI in vegetarians explained some of this risk difference…Importantly, the 50% greater risk in vegetarians translated to three more hip fractures per 1 000 people over 10 years.
“But the health benefits of a vegetarian diet, including a lower risk of cancer and cardiovascular disease, may outweigh any increases in hip fracture risk. Additionally, since there was no difference in risk between occasional and regular meat-eaters, reducing meat intake from the diet doesn’t seem to affect hip fracture risk.”
Research limitations
The study did have a number of limitations. First, this study cannot prove that following a vegetarian diet causes hip fractures.
Researchers could not independently assess vegans, who may not get enough protein and calcium in their diets. Within each group, there is also the potential for varied quality of diets, which could influence the risk for hip fractures.
Most participants were below the average ages of people with hip fractures, which may have affected the results. The age of participants could also have influenced why researchers didn’t observe changes in risk based on age.
Researchers did not distinguish between traumatic or fragility hip fractures because data on the cause of hip fractures were not available. Residual confounding is possible, as well as some of the data of participants to have changed from baseline.
Finally, there are limits on how much the results can be generalised because UK Biobank participants are healthier than the general British population, and most of the participants are white.
“Since this study was an observational study, our findings cannot show causality. Further studies are needed to confirm if vegetarian diets cause an increase in hip fracture risk and to identify why that might be. This information will help to inform risk mitigation strategies,” Webster further noted.
Study details
Risk of hip fracture in meat-eaters, pescatarians, and vegetarians: a prospective cohort study of 413 914 UK Biobank participants
James Webster, Darren Greenwood & Janet Cade.
Published in BMC Medicine on 27 July 2023
Abstract
Background
Meat-free diets may be associated with a higher risk of hip fracture, but prospective evidence is limited. We aimed to investigate the risk of hip fracture in occasional meat-eaters, pescatarians, and vegetarians compared to regular meat-eaters in the UK Biobank, and to explore the role of potential mediators of any observed risk differences.
Methods
Middle-aged UK adults were classified as regular meat-eaters (n = 258,765), occasional meat-eaters (n = 137,954), pescatarians (n = 9557), or vegetarians (n = 7638) based on dietary and lifestyle information at recruitment (2006–2010). Incident hip fractures were identified by record linkage to Hospital Episode Statistics up to September 2021. Multivariable Cox regression models were used to estimate associations between each diet group and hip fracture risk, with regular meat-eaters as the reference group, over a median follow-up time of 12.5 years.
Results
Among 413,914 women, 3503 hip fractures were observed. After adjustment for confounders, vegetarians (HR (95% CI): 1.50 (1.18, 1.91)) but not occasional meat-eaters (0.99 (0.93, 1.07)) or pescatarians (1.08 (0.86, 1.35)) had a greater risk of hip fracture than regular meat-eaters. This is equivalent to an adjusted absolute risk difference of 3.2 (1.2, 5.8) more hip fractures per 1000 people over 10 years in vegetarians. There was limited evidence of effect modification by BMI on hip fracture risk across diet groups (pinteraction = 0.08), and no clear evidence of effect modification by age or sex (pinteraction = 0.9 and 0.3, respectively). Mediation analyses suggest that BMI explained 28% of the observed risk difference between vegetarians and regular meat-eaters (95% CI: 1.1%, 69.8%).
Discussion
Vegetarian men and women had a higher risk of hip fracture than regular meat-eaters, and this was partly explained by their lower BMI. Ensuring adequate nutrient intake and weight management are therefore particularly important in vegetarians in the context of hip fracture prevention.
MedicalNewsToday article – Does a vegetarian diet increase the risk of bone fractures? (Open access)
See more from MedicalBrief archives:
More chance of hip fracture for vegetarian women – large-scale British study
Even obese vegetarians who smoke and drink have healthier biomarkers than meat-eaters
More tea, coffee and protein can lessen hip fracture risk for women – UK study
Human cells less able to absorb protein from ‘vegan’ meat’ – Ohio study