Vegan Diet and Bone Health: Current Studies

Table of Contents

The vegan diet and bone health: A study on this topic has attracted a lot of media attention. Vegans were found to have lower bone density than mixed-food eaters.

Vegan critics feel confirmed, vegans themselves react with concern. Does the study prove that a vegan diet is bad for your bones?

Study Design

The study “Vegan Diet and Bone Health – Results from the Cross-Sectional RBVD Study” by Menzel and colleagues is a small cross-sectional study. For this study, 36 vegans and 36 mixed-food eaters between the ages of 30 and 60 were recruited in Berlin. They documented what they ate over 3 days using a food diary. In addition, blood and urine samples were collected to examine various biomarkers of nutritional status. Bone density parameters were determined by ultrasound.

Results

The examinations of the nutritional status showed that the vegans studied had lower blood concentrations of vitamin A, vitamin B2, lysine, zinc, selenoprotein P (marker of selenium intake), total omega-3 fatty acids and calcium, and lower iodine excretion than the subjects following an omnivorous diet. However, with the exception of iodine, the mean values were within the normal range. Although iodine excretion was higher in the omnivorous people, it also indicated an inadequate status. The vegans had higher concentrations of vitamin K1, folate and glutamine.

Over 90 % of the vegans in the study took a vitamin B12 supplement and 50 % took a vitamin D supplement, so on average they were well supplied with these nutrients, which are also important for bone health.

Bone health was measured by ultrasound using three different parameters. One of these was significantly lower in the vegans than in the mixed-food subjects. The SI (stiffness index), which is the most informative for diagnosing osteoporosis, was also lower, but not to a statistically significant degree. The study does not provide a standard value for this, so it is not clear how much the value reflects true poor bone health. A similar study used a score of 68 to diagnose osteoporosis (Wendt et al., 2012). The Berlin vegans had an average score of 97, and the mixed-food people had a score of 104. All three of the vegans studied were in a better range than those measured in another study of healthy women without osteoporosis (Hadji et al., 1998).

In addition, measurement at the calcaneus does not allow full conclusions to be drawn about bone density at other body sites, so bone density at other sites could be different in the two groups (Wendt et al., 2012).

The marker for bone loss was the CTX level in the blood. The measurement showed significantly higher values in the vegans than in the omnivorous subjects. The reference values for this study range from 0.05 to 0.83 ng/ml, and the vegans in this study had an average value of 0.45 +/- 0.19 ng/ml, which is within the normal range (Michelsen et al., 2013). The authors state that one very high value was excluded from the calculation. This raises the question of whether other values could be falsely elevated as well. This parameter is relatively sensitive and is strongly influenced, for example, by the smallest food intake as well as the time of day when the blood sample was taken.

The lower calcium and higher parathyroid hormone (PTH) and alpha-globulin concentrations reflect the lower dietary calcium intake of vegans. The levels are within the normal range, indicating healthy regulation of calcium balance rather than necessarily poor bone health.

Possible Reasons for this Observation

The researchers also wanted to know which biomarkers of nutritional status were particularly important for bone health. They used a calculation model known as reduced rank regression (RRR).

They found that the nutrients vitamin A, vitamin B6, selenoprotein P, omega-3 fatty acids, lysine, iodine excretion, TSH and leucine were particularly relevant. Since the vegans had lower intakes of vitamin A, vitamin B6, selenoprotein P, and lysine than the participants on an omnivorous diet, the researchers suggest that this may explain the lower bone density. However, they caution that the study was too small and the computer model lacked sufficient evidence to draw firm conclusions.

Putting the Study in Context

The population studied does not allow general conclusions to be drawn. This is because very few subjects were recruited in Berlin. In addition, it is unclear whether the lower bone density measured has relevant effects on bone health and fracture risk.

Other studies of bone density in vegans show mixed results. A 2019 meta-analysis (this is a summary of multiple studies) concluded that vegans had significantly lower bone density overall and were more likely to suffer fractures. However, the results of the included studies varied, with significant effects most apparent in people over 50 years of age. On the one hand, this may indicate that people in this age group have been following a vegan diet for longer, and thus the effects are more apparent. However, it is not clear whether they have actually been vegan for longer. Older people may also be less informed; in earlier years, vitamin B12 and vitamin D supplementation, knowledge, and availability of fortified foods were not as common.

The included studies were also conducted on very different populations, so it is not possible to extrapolate to vegans living in other countries or to other populations. Also, more factors (BMI, exercise, alcohol, sun exposure) were mostly not included in the analysis.

An important caveat of the meta-analysis: Only one of the studies included diet quality. The vegans in this one study had a more health-promoting diet, and there was no significant difference in bone density between them and the omnivores. The authors concluded that a well-designed vegan diet is unlikely to lead to reduced bone density (Iguacel et al., 2019).

Another meta-analysis from 2009 found lower bone density on average with a vegan diet, but the researchers classified the effects as not clinically relevant because the overall fracture risk was not significantly increased (Ho-Pham et al., 2009).

This shows that the results of existing studies are inconclusive; many factors seem to play a role.

Aspects Relevant to Bone Health

Bone health is not determined by a single factor or the intake of one relevant nutrient. It is the interaction of many nutrients. In addition, body weight is important. Vegans often have a lower BMI, and being underweight is a risk factor for low bone density. While physical activity has a positive effect on bone density, increased exercise and sports also increase the risk of falls and fractures. Thus, an increased prevalence of fractures may occur independently of low bone density. Higher alcohol consumption and smoking can also increase the risk.

Vegans who maintain a healthy body weight, eat a balanced diet, supplement with vitamin B12 and vitamin D, get enough exercise, consume little alcohol, and do not smoke show “bone-friendly” behaviors. Because a vegan diet can provide all the nutrients needed, the effect of this type of diet on bone density depends on the composition of the food choices.

For example, those who follow the Vegan Food Pyramid reduce the risk of nutrient deficiencies and therefore low bone density.

Our Tips for Good Bone Health on a Vegan Diet

Eat a balanced diet of mainly whole or minimally-processed foods.
Pay particular attention to potentially critical nutrients.
Avoid alcohol and smoking as much as possible.
Exercise.
Maintain a healthy body weight.

Conclusion

Do bones suffer from a vegan diet?

Even if some headlines or vegan skeptics say otherwise: This study does not answer that question. It does not clearly show that the vegans studied have precariously low bone density, nor can the results be extrapolated to all vegans and vegan diets as such.

A single study can never settle a question. It can contribute to the overall picture, provide clues, and show where more research is needed. In the existing studies on the subject, vegans often, but not always, have lower bone density than people following an omnivorous diet. What causes this and whether it has negative consequences is unclear.

The overall conclusion of the existing studies is that the risk of lower bone density may be increased on a vegan diet, and vegans should pay particular attention to the nutrients relevant to bone density as well as to their general lifestyle. However, it is also clear that a vegan diet is associated with many health benefits, and with a well-planned diet, the nutrients important for bone health can be consumed in sufficient quantities.

Vegans can take advantage of the findings of this study and pay more attention to a balanced diet, paying special attention to the nutrients identified here as important.

Thus, the saying “cooking without bones” refers only to what ends up in the pot, not to the person standing in front of it.

The study can be found at the following link: Vegan Diet and Bone Health – Results from the RBVD Cross-Sectional Study.

Tired of myths and half-truths and want to learn how to evaluate such studies yourself? In our “Vegan Nutritionist” course, you will learn what really is important and science-based.