There are many good reasons to go vegetarian or vegan: some do it for ethical reasons; others for health benefits; and some as a way to help curb the climate crisis. However, even the most die-hard plant eaters will rarely point to the diet’s effect on bone and muscle density as their motivation. According to a new study, published today in the journal BMC Medicine, vegetarian women have a 33 percent higher hip fracture risk than meat-eaters – but are the results as clear-cut as they sound?
“Our study highlights potential concerns regarding risk of hip fracture in women who have a vegetarian diet. However, it is not warning people to abandon vegetarian diets,” explained James Webster, a doctoral researcher from the School of Food Science and Nutrition at the University of Leeds and lead author of the study, in a statement.
“As with any diet, it is important to understand personal circumstances and what nutrients are needed for a balanced healthy lifestyle,” he said. “Vegetarian diets can vary widely from person to person and can be healthy or unhealthy, just like diets that include animal products.”
The study followed 26,318 women over a period of around 20 years. All had completed a food frequency questionnaire originally sent out by the World Cancer Research Fund back in the mid-90s, so the researchers could sort them into three groups: meat-eaters, pescatarians, and vegetarians.
Over the whole period, 822 hip fractures were recorded in the study cohort – about three percent of the overall group. After accounting for variables like age, physical activity levels, socio-economic status, lifestyle factors like smoking, and so on, one group stood out above the rest as uniquely likely to suffer hip fractures: the vegetarians.
“Hip fracture is a global health issue with high economic costs that causes loss of independence, reduces quality of life, and increases risk of other health issues,” said study co-author Janet Cade, professor of Nutritional Epidemiology Group at the University of 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.”
So the correlation was certainly present – but what about the causation? Well, here’s where things get a little tricky. Although it’s true that vegetarian diets often have lower levels of nutrients like protein, calcium, and other micronutrients linked with bone and muscle health, the study notes that the differences in risk between meat-eaters and vegetarians “were not explained by differences in key nutrient intakes related to bone health between vegetarians and regular meat-eaters, implying the potential importance of other unaccounted factors.”
One of those factors may be the difference in BMI between the two groups: vegetarians, on average, have a lower BMI than meat-eaters, and that’s been shown to increase a person’s risk of hip fracture risk.
Then there are the factors that were beyond the scope of the study: “supplemental sources of specific nutrients and circulating vitamin D concentrations could differ between vegetarians and non-vegetarians and may impact the risk of hip fracture,” the study notes, “but could not be accounted for in this analysis due to a lack of data.”
The same is true for certain hormones associated with hip fracture risk – they may have been a factor between the groups, but the researchers simply didn’t have the information to consider them.
“This study is just part of the wider picture of diet and healthy bones and muscles in older age,” biostatistician and study co-author Darren Greenwood pointed out.
“Further research is needed to confirm whether there could be similar results in men, to explore the role of body weight, and to identify the reasons for different outcomes in vegetarians and meat-eaters.”