Long-term adherence to a plant-based diet was not tied to a greater risk of hip fracture and some plant-based regimens may actually reduce the risk, a large cohort study of postmenopausal women in the United States suggested.
Not all plant-centered regimens are healthful, however, and this study factored dietary quality into risk.
Writing in JAMA Network Open, the study authors compared the lowest to highest quintiles of Plant-Based Diet Index scores. They found the most recent intake of a healthy plant-based diet (hPDI) to be associated with a somewhat lower (21%) risk of fracture while the most recent intake of its unhealthy counterpart (uPDI) was linked to a somewhat higher (28%) risk.
“In addition, higher baseline scores in the uPDI were associated with higher risk of hip fracture,” wrote the researchers, led by Mercedes Sotos Prieto, PhD, a nutritional epidemiologist in the Department of Preventive Medicine and Public Health at the Autonomous University of Madrid.
Plant-based diets, characterized by higher consumption of plant foods and lower or no intake of animal foods, have raised concerns about their potential harm to bone health. In a recent meta-analysis, vegetarians, but particularly vegans with no consumption of any animal food, had a higher fracture risk and lower bone mineral density compared with omnivores.
Another study found that compared with meat eaters, fish eaters and vegetarians had a higher risk of hip fractures. These analyses, however, did not assess the quality of the plant-based diets.
Courtesy Dr. Sotos Prieto
Dr. Mercedes Sotos Prieto sits at a table with an arrangement of nutritious foods.
“We hypothesized that the differences in the quality of the plant-based diets — whole grains, fruits, and vegetables vs refined carbohydrates or snacks, which are both plant-based but very different, would be important in the association for the risk of hip fracture,” Dr. Sotos Prieto said in an interview.
Study details
Her study drew on data from 70,285 postmenopausal White women who were in the US Nurses’ Health Study from 1984 through 2014; data were analyzed from Jan. 1 to July 31, 2023.
The mean age of the nurses was 54.92 years, and 2038 cases of hip fracture were reported during the study over as long as 30 years of follow-up.
Healthy plant foods included whole grains, fruits, vegetables, nuts, legumes, vegetable oils, and tea or coffee and received positive scores, whereas less healthy plant foods such as fruit juices, sweetened beverages, refined grains, potatoes, sweets, or desserts and animal foods received reversed scores. Dietary and lifestyle information was collected by self-reported questionnaires.
Individuals with higher hPDI scores were leaner, more physically active, less likely to be smokers, and more likely to use vitamin and calcium supplements. Not surprisingly, they also had higher intakes of dietary calcium and healthy plant foods and had lower intake of less healthy plant foods. “It’s plausible that reverse causation may account for the risk associations, as individuals with underlying health conditions that predisposed them to higher fracture risk may have changed their diet,” Dr. Sotos Prieto said. “In addition, baseline diet may reflect diet early on, which could be an important predictor of bone mineral density when there was more active bone turnover.”
Lack of information precluded adjustment for the use of anti-osteoporotic medication.
Neither the hPDI, with a hazard ratio (HR) for highest vs lowest quintile of 0.97 (95% confidence interval, 0.83-1.14) nor the uPDI, with an HR for highest vs lowest quintile of 1.02 (95% CI, 0.87-1.20) for diet adherence over the long term was associated with hip fracture risk.
For recent dietary intake in the highest vs lowest quintiles, however, the hPDI was associated with a 21% lower risk of hip fracture: HR, 0.79 (95% CI, 0.68-0.92; P = .02 for trend). In contrast, the uPDI was associated with a 28% higher risk: HR, 1.28 (95% CI, 1.09-1.51; P = .008 for trend).
Future studies in other populations are needed to confirm the results and enhance their generalizability, Dr. Sotos Prieto said. “Investigating the temporal dynamics of dietary patterns and their effects by examining how recent dietary changes may impact health outcomes over different timeframes is important.” In the meantime, people wishing to follow a plant-based diet should make sure it features high-quality foods.
This work was supported by Instituto de Salud Carlos III, State Secretary of Research, Development and Innovation of Spain, and the European Research Funds and European Social Fund, the Agencia Estatal de Investigación, the National Institutes of Health, and a Ramón y Cajal contract from the Ministry of Science, Innovation, and Universities. A coauthor reported a patent pending. No other disclosures were reported.