Osteoporosis, a metabolic bone disease characterized by reduced bone mineral density (BMD) and deterioration of bone microarchitecture, affects over 200 million individuals globally and leads to increased risk of bone pain and fragility fractures. Preventing osteoporosis has become a significant public health concern, especially considering the low percentage of patients receiving medication treatment due to concerns about side effects and the fragmented nature of healthcare systems. Plant-based dietary patterns have been recommended for their potential health and environmental benefits, but their association with bone health requires careful exploration. This article delves into the relationship between vegan diets and osteoporosis risk, considering various factors and providing evidence-based recommendations.
Understanding Osteoporosis
Osteoporosis is not simply a "dairy deficiency" or a "calcium deficiency" disease. It is a complex condition influenced by multiple factors. While calcium is essential, it is only one piece of the puzzle. Osteoporosis is characterized by low bone mass and low bone density, leading to an increased risk of fractures, particularly in people 50 years of age or older. Taking preventive measures from childhood and early adulthood is crucial for mitigating the risk of osteoporosis later in life.
The Vegan Diet: A Detailed Look
Plant-based dietary patterns, characterized by higher intake of plant foods and lower consumption of animal foods, have been widely recommended as healthy dietary options. A plant-based diet has been shown to improve the diversity and composition of the intestinal microbiota, leading to increased production of specific metabolites that exert beneficial effects on host health, including at the intestinal and systemic levels. Accumulating evidence suggests that a plant-based diet plays a positive role in preventing chronic diseases such as type 2 diabetes mellitus (T2DM), hypertension, and cardiovascular disease.
However, a plant-based diet has been found to include lower levels of calcium, vitamin D, vitamin B-12, protein, and n-3 fatty acids, which are all crucial for maintaining bone health. As a result, individuals following plant-based diets may exhibit lower BMD and higher risk of fractures. In a recent study of participants in the 2007-2010 National Health and Nutrition Examination Survey (NHANES), self-identified vegetarians had significantly lower BMD than non-vegetarians. Additionally, a meta-analysis found that individuals following a plant-based diet exhibited lower BMD and higher rates of fractures in the femoral neck and lumbar spine than those following an omnivorous diet.
In previous studies, plant-based diets were typically defined as “vegetarian” diets, with participants being divided into two groups: those who consume any animal-based products and those who do not. However, transitioning to a completely animal-free diet presents a considerable challenge for many individuals, attributable to cultural acculturation and the affordability of plant-based foods. The pressure to assimilate into American society and adapt to the fast-paced lifestyle can make it challenging to avoid consuming animal-based foods, particularly during social gatherings. Furthermore, the cost of plant-based products can be higher than that of animal products in certain regions, exerting a notable influence on people’s dietary choices.
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Recently, Satija et al. conceptualized a graded dietary pattern comprising three plant-based dietary indexes: overall plant-based diet index (PDI), healthy plant-based diet index (hPDI), and unhealthy plant-based diet index (uPDI). The PDI reflects an overall trend towards a progressive increase in the proportion of plant-based foods, accompanied by a gradual decrease in the intake of animal-based foods. The hPDI and uPDI distinguish between healthy and unhealthy plant-based foods, addressing the limitations of previous studies that treated all plant-based foods equally. These three plant-based indexes provide a more comprehensive approach to assess nutrient density and the impact of dietary changes on health, guiding individuals toward more sustainable and healthier diets.
Impact of Plant-Based Diets on Bone Health: Recent Findings
A study published in JAMA Network Open on February 29 examined the diets and bone health of 70,285 postmenopausal women enrolled in the Nurses’ Health Study from 1984 through 2014. Each participant’s diet was scored based on adherence to a healthy plant-based diet (hPBD) or unhealthy plant-based diet (uPBD). A high hPBD score indicated high intake of whole grains, fruits, vegetables, nuts, legumes, vegetable oils, and coffee or tea; a high uPBD score indicated high intake of fruit juices, sweetened beverages, refined grains, potatoes, and sweets or desserts. The study found no association between long-term adherence to a plant-based diet and risk of hip fracture. However, when the researchers focused only on participants’ recent food intake, they saw a difference in the risk of hip fracture between those whose recent diet was healthy versus unhealthy. Those with high current hPBD scores had a 21% lower risk of hip fracture than those with low current hPBD scores.
The plant-based dietary pattern has been recommended for its potential health and environmental benefits, but its association with bone loss needs to be further explored. One study aimed to investigate the association between three plant-based diet indexes and bone loss in 16,085 adults, using data from the National Health and Nutrition Examination Survey. Three plant-based diet indexes (PDI, hPDI, and uPDI) were calculated from two NHANES 24-h dietary recall interviews, to characterize a plant-based diet. A multinomial logistic regression model was used to estimate the odds ratios (OR) and 95% confidence intervals (95% CI). Higher hPDI and PDI were associated with increased risk of bone loss (ORQ5 vs. Q1 = 1.50; 95% CI: 1.24-1.81 for hPDI; ORQ5 vs. Q1 = 1.22; 95% CI: 1.03-1.45 for PDI), while higher uPDI was associated with increased risk of osteoporosis (ORQ5 vs. Q1 = 1.48; 95% CI: 1.04-2.11). A harmful association between plant-based diet indexes (hPDI and PDI) and osteopenia was observed at the lumbar spine rather than the femoral neck.
Key Nutrients for Bone Health: A Vegan Perspective
There’s no question that calcium is crucial for bone health. Calcium is the predominant mineral in bone and is necessary for the building and maintenance of bone. If dietary calcium isn’t available (or is too low), the body pulls calcium out of bones, thereby weakening them. Vegan diets need to be well-planned to ensure adequate calcium intake. Adults need 1,000mg of calcium per day, while women over the age of 50 and men over the age of 70 need 1,200mg.
Managing veganism and osteoporosis is more complex than adequate calcium intake. Many other important nutrients are involved and play crucial roles in building vegan bone density.
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- Vitamin D: Vitamin D is directly involved in the building of strong bones because it helps us absorb calcium. The daily requirement of Vitamin D is 600IU. You can obtain vitamin D from fortified foods (like fortified breakfast cereal or non-dairy milks, for example). If you live in Canada, you should take a 1,000-2,000 IU vitamin D supplement during the winter months (October-April) for optimal health because sunlight exposure and fortified foods will likely not be enough to meet your vitamin D needs alone.
- Vitamin K: Vitamin K stimulates bone formation. Conveniently, you can find Vitamin K in the same foods that have high calcium, like dark leafy greens, beans, and soy products. These foods can help increase bone density.
- Potassium: Potassium decreases calcium loss and increases the rate of bone building. Oranges, bananas, potatoes, and many other fruits and veggies are all rich sources of potassium. As a rule of thumb, whole foods are typically high in potassium, while processed foods are low in potassium.
Factors Affecting Calcium Absorption
Some vegetables such as spinach and Swiss chard contain compounds called oxalates that can reduce the amount of calcium your body absorbs. Phytates are another compound causing the same effect on calcium absorption, found in some grains and legumes such as beans and lentils. This might mean you absorb some nutrients less efficiently if damage has occurred, and so calcium requirements are higher.
The Role of Exercise
Lifestyle choices have a huge impact on bone health. Physical activity (specifically, weight-bearing resistance exercise) intensifies the bone-building process and helps maintain bone density as we age. Later in life, activities that target muscle strength and balance can help prevent falls and fractures. There are special nutritional considerations for athletes on a plant-based diet and osteoporosis. For example, female athletes at high risk for early osteoporosis need additional calcium (1,500mg per day) to support their bone health.
During the menopause muscle mass also reduces, which may lead to weight gain and affect bone health. A mix of resistance (e.g. weight training) and weight-bearing exercise (e.g. yoga) with impact (e.g.
Addressing Common Concerns
Previous research, namely the Plant-based diets and long-term health: findings from the EPIC-Oxford study suggested that vegans have a higher risk of fractures (broken bones) than those following a vegetarian or omnivorous diet. Some recent studies have since found that vegans with a ‘healthful, well-planned' diet containing regular consumption of whole grains, fresh fruit and vegetables, nuts and legumes, did not have lower bone density or increased risk of fractures compared to vegetarians or omnivores.
Whilst PBDs can be considered ‘ultra-processed’, the term itself is not very helpful for classifying the health or nutritional profile of foods. The processing involved in PBDs includes fortification with additional vitamins and minerals such as calcium, iodine and vitamin D.
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Practical Tips for Vegans to Maintain Bone Health
A well-planned plant-based diet can protect against osteoporosis. Here are a few key tips:
- Eat a healthy, balanced diet: An eating pattern that contains a variety of whole grains, healthy fats, protein, and fruits and veggies will contain important nutrients for protecting bone health.
- Eat dark leafy greens daily: Dark leafy greens are packed with important nutrients like vitamins A, C, and E, as well as calcium, iron, magnesium, and potassium.
- Drink calcium-fortified beverages: Choose calcium-set tofu, and eat almonds, tahini, and blackstrap molasses.
Tofu is something that CAN member Linda, 63, has worked into her vegan diet. Beans, lentils, nuts and quinoa are also protein packed.
NHANES Study: Methodology and Results
The present study utilized publicly available data from the NHANES, affiliated with the National Center for Health Statistics (NCHS) of the Centers for Disease Control and Prevention (CDC). The NHANES was designed to evaluate nutrition status and the prevalence of disease in the US population. Due to the unavailability of BMD data for the femoral neck in 2011-2012 and 2015-2016, subject information was collected from five 2-year NHANES cycles (2005-2006, 2007-2008, 2009-2010, 2013-2014, and 2017-2018). Inclusion criteria were as follows: (i) participants aged ≥20 years; (ii) participants with complete BMD and dietary interview data; (iii) participants with reported energy intake levels within predefined limits (≥600 and ≤3500 kcal/d for women and ≥800 and ≤4200 kcal/d for men). Participants with energy intakes outside these limits were excluded from the analysis, as such extremes in energy intake may not represent the general population and could introduce bias into the results. We identified 50,463 potential participants from the five NHANES cycles (NHANES 2005-2006, 2007-2008, 2009-2010, 2013-2014, and 2017-2018). After excluding the participants who did not meet the inclusion criteria, we ultimately recruited 16,085 participants.
All subjects had BMD (g/cm2) measured at the lumbar spine (L1-L4) and the femoral neck using a dual-energy X-ray absorptiometry densitometer (Hologic QDR-4500A; Bedford, MA, USA). Participants were excluded from the DXA examination if they satisfied any of the following criteria: (i) participants who were pregnant; (ii) participants who weighed more than 450 pounds; (iii) participants who had a self-reported history of radiographic contrast material in the past 7 days; (iv) participants with bilateral hip fractures, replacements, or pinning. As recommended by the World Health Organization, the mean BMD of non-Hispanic white females aged 20-29 years from NHANES III was used as the reference group for the femoral neck, while the mean BMD of non-Hispanic white females aged 30-39 years from NHANES was used as the reference group for the lumbar spine. In addition, the 16,085 participants were classified into three categories (normal, osteopenia, and osteoporosis) based on the minimum BMD T-score of the two measuring sites. Osteopenia was diagnosed according to a BMD T-score between −1.0 and −2.5, while osteoporosis was diagnosed according to a BMD T-score ≤ −2.5.
Dietary intake data were collected from two NHANES 24-h recall interviews and extracted after conversion to the respective food equivalents in the food-pattern-equivalence database. Additionally, dietary intake was estimated using the average of two 24-h recall data. To calculate the three plant-based diet indexes, we assessed the intake of 15 food groups, which were divided into three categories: healthy plant-based foods, unhealthy plant-based foods, and animal-based foods. We assigned positive or reverse scores to each food item based on the quintile of intake. Each subject’s scores were summed to obtain a score for each index, with a theoretical range of 15 to 75. Finally, these index variables were treated as continuous (per 10-unit increment) and categorical (in quintiles), respectively.
Participants’ demographical characteristics (age, sex, ethnicity, educational level, poverty income ratio (PIR), body mass index (BMI), and marital status), lifestyle (smoking status and physical exercise), and history of disease (T2DM, hypertension, chronic kidney disease (CKD), cancer, and history of fracture) were considered as covariates in the present study. PIR was calculated as the ratio of the midpoint of the household’s self-reported income to the corresponding poverty threshold for the household. Based on serum cotinine levels, we defined three categories of (i) non-smoker (<1.0 ng/mL); (ii) environmental tobacco smoke (ETS) exposure (1.0-9.9 ng/mL); (iii) current smoker (≥10 ng/mL). Following the WHO guidelines, we defined four physical activity categories as: (i) inactive (participants with no regular physical activity); (ii) insufficient (<8.33 MET-hours/week); (iii) moderate (8.33-16.67 MET-hours/week); (iv) high (>16.67 MET-hours/week). Participants were diagnosed with T2DM if they satisfied any of the following criteria: (i) self-reported doctor diagnosis of diabetes or treatment with hypoglycemic drugs; (ii) fasting plasma glucose (FPG) of ≥7.0 mmol/L; (iii) 2-h blood glucose after oral glucose tolerance test (OGTT) of ≥11.1 mmol/L; (iv) hemoglobin A1c (HbA1c) of ≥6.5%; (v) any one of three random blood glucose test results ≥11.1 mmol/L. CKD was diagnosed if participants met any of the following criteria: (i) estimated glomerular filtration rate (eGFR) of <60 mL/min/1.73m2; (ii) albumin-to-creatinine ratio (ACR) of >30 mg/g. Hypertension was considered present if participants met either of the following criteria: (i) self-reported physician-diagnosed hypertension or treatment with anti-hypertensive medication; (ii) average of three systolic blood pressures (SBP) of ≥140 mmHg or average of three diastolic blood pressures (DBP) of ≥90 mmHg. Covariate data for cancer and history of fracture were obtained from the respective questionnaires administered to the study participants.
All analyses used sampling weights recommended by the NCHS to account for the complex NHANES survey design. Initially, categorical variables were described by the frequency (percentage) of participants, and the differences between groups were compared using the chi-square test. Secondly, we measured the associations between the three plant-based diet indexes and the BMD T score, using Spearman’s correlation coefficients, and induced the corresponding 95% confidence intervals. Correlation coefficients were classified into five categories: very strong (0.90-1.00), strong (0.70-0.89), moderate (0.40-0.69), weak (0.10-0.39), and negligible (0-0.10). A significance test was necessary to control for the possibility that an observed difference between two correlations may be due to chance alone. Overlapping correlations in dependent groups were compared using Hittner, May, and Silver’s modification of Dunn and Clark’s z test and Zou’s confidence interval test. In addition, multinomial logistic regression analysis was applied to examine the relationship between the three plant-based diet indexes and different BMD statuses. We developed two separate models for the association between each plant-based diet index and different BMD status: (1) Model 1: adjusted for age, sex, and ethnicity; (2) Model 2: Model 1 plus education, marital status, PIR, BMI, smoking status, physical exercise, hypertension, T2DM, CKD, cancer, and history of fracture. We further conducted sensitivity analyses to evaluate the robustness of our findings. First, subgroup analyses were performed for variables associated with different BMD statuses, with stratification factors including age (20-50, 50-65, ≥65), sex (male, female), ethnicity (non-Hispanic black, non-Hispanic white, Mexican American, other), T2DM (yes, no), CKD (yes, no), history of fracture (yes, no), and smoking status (non-smoker, current smoker). Second, we excluded participants who had previously taken anti-osteoporotic and estrogenic drugs, as the use of these medications may affect the accuracy of the results. Then, we additionally adjusted the models for more potential confounders, including menopausal status, corticosteroid usage, and dietary supplements (vitamin D and calcium). Next, by calculating E values we evaluated the possibility of unmeasured confounding between the three plant-based dietary indexes and bone loss. All statistical tests were two-tailed, and a statistically significant difference was defined as p < 0.05. All analyses were performed using R software (4.1.0, R core team).
A total of 16,085 participants were included in this study, among whom 8238 (51.22%) were female, and 4631 (28.79%) were over 65 years of age, regardless of gender.
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