1. In a cohort of UK-based women, vegetarians/vegans, but not occasional meat-eaters or pescatarians, had a higher risk of hip fracture compared to regular meat-eaters.
2. The association between diet type and hip fracture risk was not affected by BMI.
Evidence Rating Level: 2 (Good)
Study Rundown: Hip fractures are becoming increasing prevalent as global populations age. They are most common in elderly women and greatly impact mobility, morbidity, and mortality. The number of vegetarians globally is also increasing. Vegetarian diets are characterized by lower intake of certain nutrients, such as total protein, calcium, vitamin D, vitamin B12, and omega-3 fatty acids, which are more easily obtained through animal products. Studies have also shown that pescatarian and vegetarian diets are associated with lower average body mass index (BMI) than meat-rich diets. Consequently, there are growing concerns regarding bone health and fracture risk in individuals on meat-free diets. Few studies have compared the risk of hip fracture in vegetarians and non-vegetarians. Consequently, this study used data from the United Kingdom Women’s Cohort Study (UKWCS) to investigate the risk of hip fracture in occasional meat-eaters, pescatarians, and vegetarians compared to regular meat-eaters in middle-aged UK women and to determine if associations between diet and fracture risk are modified by BMI. Over 26,000 UK-based women aged 35-69 years were assessed at recruitment using a self-administered 217-item food frequency questionnaire (FFQ). Based on responses, participants were classified as regular meat eaters, occasional meat eaters, pescatarians, or vegetarians/vegans. Participants’ diet and lifestyle characteristics were linked with their hospital episode statistics up to March 31, 2019. A total of 822 hip fracture cases were observed. It was found that vegetarians/vegans, but not occasional meat-eaters or pescatarians, had a higher risk of hip fractures than regular meat-eaters. There was no evidence of effect modification by BMI in any diet group. Further research is needed to confirm this in other populations, such as men and non-European groups.
In-Depth [Prospective Cohort Study]: This prospective cohort study used data from UKWCS, which explored diet and lifestyle in relation to chronic disease outcomes among a large cohort of British, Scottish, and Welsh women. In total, 35,372 women, aged 35-69 years, responded to a postal questionnaire that collected dietary and lifestyle data at recruitment (1995-1998). After exclusions, data from 26,318 women was included in this study. Dietary group was determined based on results from a self-administered 217-item FFQ done at baseline and subsequently validated by comparison with 4-day weighted food diaries and a repeat FFQ 3 years after baseline. Based on responses, participants were classified by regular meat-eaters (ate meat ≥ 5 times/week), occasional meat-eaters (ate meat < 5 times/week), pescatarians (ate fish but not meat), vegetarians (ate eggs or dairy but not meat or fish), or vegans (did not eat meat, fish, eggs, or dairy). Vegetarians and vegans were combined due to a small number of vegan participants (n=130). The primary outcome of hip fracture incidence was determined using hospital records up to March 2019. Cox regression models were used to estimate the associations between each diet group and hip fracture risk over a median follow-up time of 22.3 years. A total of 822 hip fracture cases were observed, corresponding to 3.1% of the cohort. Regular meat-eaters reported the highest absolute dietary intakes of protein, vitamin D, and vitamin B12, whilst vegetarians reported the lowest. Calcium intakes were similar across the diet groups. BMI was lower in vegetarians (mean (standard deviation, SD) 23.3 (3.9 kg/m2)) and pescatarians (23.3 (3.5 kg/m2)) than in regular meat-eaters (25.2 (4.4 kg/m2)). After adjustment for confounders, vegetarians (HR 1.40 (95% CI 1.11, 1.78)) but not occasional meat-eaters (1.03 (0.88, 1.21)) or pescatarians (1.04 (0.81, 1.34)) had a greater risk of hip fracture when compared with regular meat-eaters (vegetarians 1.33 (1.03, 1.71); occasional meat-eaters 1.00 (0.85, 1.18); pescatarians 0.97 (0.75, 1.26)). Whilst the risk of hip fracture was 46% higher in participants with BMI < 23.5 kg/m2 compared to BMI ≥ 23.5 kg/m2, there was no evidence of effect modification by BMI on hip fracture risk in each diet group when BMI was modelled categorically (p-interaction = 0.3) or linearly (p-interaction = 0.6). These results will help inform public health policies and interventions aiming to reduce hip fracture risk among vegetarians/vegans.
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