Vegetarian Diet May Up Risk for Hip Fracture in Women

Women who consume a vegetarian diet had a 33% greater risk of hip fracture compared to "regular meat-eaters," according to findings from a new study of more than 26 000 women in the UK. Lower body mass index (BMI) in this population may partly expalin the elevated hazard, say study authors.

Published in BMC Medicine, the study by researchers from the University of Leeds assessed the risk of hip fracture in women who ate a vegetarian diet with those who ate a pescetarian diet, those who were occasional meat-eaters and those who ate meat regularly.

“Plant-based diets have been linked with poor bone health, but there has been a lack of evidence on the links to hip fracture risk. This study is an important step in understanding the potential risk plant-based diets could present over the long-term and what can be done to mitigate those risks,” said study coauthor professor Janet Cade, leader of the Nutritional Epidemiology Group in the School of Food Science and Nutrition at Leeds.

“Plant-based diets have been linked with poor bone health, but there has been a lack of evidence on the links to hip fracture risk. This study is an important step in understanding the potential risk plant-based diets could present over the long-term and what can be done to mitigate those risks."

As context for their research, the University of Leeds researchers cite conflicting findings on the impact of vegetarianism on bone health. While quality of diet will vary among vegetarians, they write, consumption of vegetable protein is generally high in this population and there are studies linking that protein to reduced risk of hip fracture. Those diets, the authors add, however, are also characterized as low in nutrients associated with optimal bone mineral density and those are more abundant in animal protein.

In what they describe as the first prospective study to compare the risk of hip fracture among the 4 dietary patterns, the researchers were also interested in whether any potential associations between diet type and risk would be modified by body mass index (BMI).

The team, led by James Webster, a doctoral researcher from the School of Food Science and Nutrition at Leeds, tapped the UK Women's Cohort Study (UKWCS) for data. After exclusions for missing covariate information among the original 30 244 participants there were 26 318 women aged 35 to 69 years in the final cohort. The average age of the group was 52.1 years.

Investigators classified the participants as regular meat-eaters (≥5 servings/ week), occasional meat-eaters (<5 servings/week), pescatarian (ate fish but not meat), or vegetarian (ate neither meat nor fish) based on responses to a validated food frequency questionnaire upon original enrollment into the UKWCS, between 1995 and 1998.

Diet groups

• Meat eaters 13 984 (46.2%)
• Occasional meat eaters 8000 (26.5%)
• Pescetarian 3867 (12.8%)
• Vegetarian 4393 (14.5%)

Average BMI of the cohort was 24.4 3 kg/m², mean daily caloric intake, 2300 calories, and mean protein intake 88.1 g/day. Participants’ diet and lifestyle characteristics were linked with hospital episode statistics to identify incident hip fracture throught March 31, 2019.

FINDINGS

Participants were followed for a median of 22.3 years during which there were 822 hip fractures observed or approximately 3.1% of the full cohort.

In unadjusted analysis the investigators found that when they were compared with regular meat-eaters, vegetarians (hazard ratio [HR] 1.40 (95% CI 1.11 - 1.78)) but not occasional meat-eaters (HR 1.03 (0.88 - 1.21)) or pescatarians (HR 1.04 (0.81 - 1.34)) had a greater risk of hip fracture. The associations were slightly attenuated after adjusting for potential confounding variables, but the higher risk of hip fracture among vegetarians remained and was statistically significant, 1.33 (1.03 - 1.71); occasional meat-eaters, 1.00 (0.85 - 1.18); pescatarians, 0.97 (0.75 - 1.26).

The investigators report that mean BMI was lower in vegetarians (23) and pescatarians (23.3) than in regular meat-eaters (25.2). When they assessed risk of hip fracture according to BMI, Webster et al found that the risk of hip fracture was 46% higher in participants with BMI <23.5 compared to BMI ≥23.5. However, they observed no evidence of effect modification by BMI on hip fracture risk in any of the diet groups when they modelled BMI categorically (p-interaction = 0.3) or linearly (p-interaction = 0.6)

The study authors suggest that the finding of higher risk of hip fracture in vegetarians compared to regular meat-eaters may be partly explained by the differences in body anthropometrics between the diet groups. And, they add, despite the absence of clear evidence that BMI had a modifying effect on the associations between diet groups and hip fracture risk, analysis revealed that lower mean BMI in vegetarians partly explained their higher risk.

The study authors suggest that the finding of higher risk of hip fracture in vegetarians compared to regular meat-eaters may be partly explained by the differences in body anthropometrics between the diet groups.

“Our study highlights potential concerns regarding risk of hip fracture in women who have a vegetarian diet,” commented Webster in a statement. “However, it is not warning people to abandon vegetarian diets. As with any diet, it is important to understand personal circumstances and what nutrients are needed for a balanced healthy lifestyle.”

The research team recommends further research that will focus in particular on the roles of BMI and nutrients abundant in animal-sourced foods “so that public health interventions and policy guidelines aiming to reduce hip fracture risk in vegetarians through dietary change or weight management can be formed.”

Reference: Webster J, Greenwood DC, Cade JE. Risk of hip fracture in meat-eaters, pescatarians, and vegetarians: results from the UK Women’s Cohort Study. BMC Med. 2022;( 20)275. doi.org/10.1186/s12916-022-02468-0