- The study behind the headlines
- What to keep in mind when reading the study’s conclusions?
- What do authorities say?
Recent news stories reported that women who follow a vegetarian diet are more likely to suffer hip fractures than those who eat meat, suggesting nutritional deficiencies and lower body mass index (BMI) as possible causes. Meatless diets are becoming increasingly popular in Western countries, possibly due to increasing evidence of reduced risks of several chronic diseases and a lower environmental footprint of vegetarian diets compared to omnivorous diets. So, should you really abandon a vegetarian diet according to these new findings? Here are a few things to keep in mind when reading the headlines.
The study behind the headlines
The study behind the news was carried out by researchers from the University of Leeds in the UK with the aim to investigate the risk of hip fracture in occasional meat-eaters, pescatarians and vegetarians compared to regular meat-eaters in middle-aged UK women, as well as to determine if potential associations between each diet group and hip fracture risk differ across levels of BMI.1
The current study used health and lifestyle data from the UK Women’s Cohort Study, which is a large long-term study involving 500,000 women (aged 35-69 years) from England, Scotland and Wales aimed at exploring the links between diet and chronic disease. The study started during the 1990s with participants filling in a so-called food frequency questionnaire (FFQ) about their usual eating habits over the past year. Based on their responses, women were classed as regular meat eaters (≥5 times per week), occasional meat eaters (<5 times per week), pescatarian (ate fish but no meat) and vegetarian or vegan (ate neither meat nor fish). The researchers then followed these participants up over a period of, on average, 22 years, and combined data from hospital records to identify cases of hip fracture.
After the follow-up period had passes, the researchers analysed the data from 26,318 women who had complete data. They found that vegetarians and vegans, but not occasional meat eaters or pescatarians, had a 33% higher risk of hip fracture compared with the regular meat eater group. Within this association, the study has considered multiple factors such as ethnicity, smoking status, level of physical activity, menopausal status, reproductive history and other diseases that could potentially influence the hip fracture outcome. Further analysis considering BMI, specific vitamins and minerals (e.g., calcium and vitamin D) or dietary fatty acids found that none of these factors made a meaningful difference to the results.
The researchers suggest that future exploration of other factors (e.g., supplemental sources of specific nutrients and circulating vitamin D concentrations) beyond BMI and nutrient intakes could shed light on the observed associations. Besides, further research is needed to look at the link in other population groups, such as men and non-European populations.
What to keep in mind when reading the study’s conclusions?
- The study does not prove that vegetarian diets are the cause of hip fracture.
Despite careful attempts to account for multiple health and lifestyle factors such as ethnicity, smoking status, level of physical activity etc., that could potentially influence the hip fracture outcome, observational studies such as this, cannot prove direct cause and effect. Furthermore, other unmeasured dietary or lifestyle factors may be involved in the intricate link with hip fractures. Besides, self-administered questionnaire responses from the FFQ may introduce inaccuracies and it is difficult to ensure that they fully reflect a person’s health, lifestyle and long-term dietary patterns.
- There was no clear evidence that low BMI or nutrient deficiencies provide the answer.
Media reports and the accompanying press release discuss lower BMI or nutritional deficiencies as potential explanations for the observed results. However, it is important to highlight that the study thoroughly explored the individual effect of such factors, with none having a significant impact on the results (i.e., the higher risk of hip fracture in vegetarians was not explained by any dietary nutrient intake nor entirely by BMI). Despite previous research showing an established association between osteoporosis (a condition which predisposes to fracture) and lower BMI or low calcium intake, for example, this specific study does not provide such evidence.
- The results might not be applicable to current populations.
The popularity of vegetarian and vegan diets and food availability has increased considerably over the past 20 years. Therefore, food and nutrient intakes in vegetarians in recent years could differ from the periods in which data were collected. As a result, the outcomes cannot be completely generalised to modern-day vegetarians. Also, as the authors acknowledge, neither can the findings be applied to non-white, non-European populations or to men. Moreover, vegetarians and vegans could not be analysed separately due to few study participants, including only 130 vegans (0.5% of women), 5 of whom developed hip fractures.
- The wider benefits of a high fruit and vegetable intake were not explored.
Despite some media outlets reporting that ‘being vegetarian might be bad for your health later in life’ the study has only looked at the link between being a vegetarian and hip fracture. It does not explore the various health benefits associated with a diet high in fruit and vegetables, nor conversely, the adverse effects that have been associated with a diet high in red and processed meat. As such, any small increased risk of hip fracture – if a true link – may be outweighed by the positive effects of adopting a vegetarian diet.
What do authorities say?
- The European osteoporosis guidelines (2019) list risk factors for fracture probability. These include, for example, gender, low BMI, prior fragility fracture, parental history of hip fracture, steroid treatment, current smoking and alcohol intake. For lifestyle prevention they advise regular weight-bearing exercise and ensuring adequate daily calcium intake (800-1200 mg), dietary protein and vitamin D (800 IU or 20 mcg for postmenopausal women), using supplements if necessary. The guidance makes no mention of specific dietary patterns, such as vegetarian or vegan diets.2
- In 2021 the WHO published a report on the health impact of plant-based diets (including vegetarian and vegan diets). Overall, they recommend a predominantly plant-based diet low in salt, saturated fats and added sugars as part of a healthy lifestyle. They state that such diets lower the risk of early mortality and protect against chronic diseases, supporting the evidence that high red and processed meat is associated with risk of chronic disease. However, WHO highlights that strict vegan diets raise concerns about nutrient deficiencies, including vitamins D and B12 and calcium.3
- EUFIC also provides a summary (2021) on plant-based diets, their health and environmental benefits, emphasising that transitioning to a plant-based diet should focus on increasing healthy plant foods and be less concerned with reducing animal products. It also highlights that plant-based diets can still be unhealthy if high in fat, sugar and salt, and that particular care is needed if following a vegan diet to ensure adequate nutrition.
- Webster, J., Greenwood, D. C., & Cade, J. E. (2022). Risk of hip fracture in meat-eaters, pescatarians, and vegetarians: results from the UK Women’s Cohort Study. BMC medicine, 20(1), 1-10.
- Kanis, J. A., Cooper, C., Rizzoli, R., & Reginster, J. Y. (2019). European guidance for the diagnosis and management of osteoporosis in postmenopausal women. Osteoporosis International, 30(1), 3-44.
- World Health Organization. (2021). Plant-based diets and their impact on health, sustainability and the environment: a review of the evidence: WHO European Office for the Prevention and Control of Noncommunicable Diseases. Copenhagen: WHO Regional Office for Europe.