Attention required for strong bones with a vegan diet

What is the effect of a vegan diet on bone mineral density? Researchers Iguacel et al. (2018) have investigated the effect of different diets on bone health in a systematic review and meta-analysis.

Summary | The diet has an effect on bone mineral density, as again appears from a systematic review and meta-analysis by Iguacel et al. (1) This meta-analysis made a comparison between bone health among vegans, vegetarians and omnivores. The researchers conclude that it is particularly vegans who have a lower bone mineral density than omnivores. The researchers state that vegans probably have a lower intake of certain nutrients such as calcium, high quality proteins, vitamin B12, vitamin D and retinol that are only found in larger quantities or exclusively in animal products. This can have an effect on bone health, according to the researchers.

During life, bone tissue is constantly broken down (resorption) and again built up (formation) to repair it after minor ‘damage’ and adapt the strength of the bone depending on the load it is subjected to. Bone formation is greater than bone resorption from birth up to the age of approximately 30 years, when bone density reaches its peak bone mass (PBM). Genetic factors and various lifestyle factors have an influence on the peak bone mass and bone mineral density (BMD). As regards lifestyle factors, sufficient physical movement, in particular movement with the bones being loaded such as while running, and a varied diet with sufficient calcium, vitamin D and protein are factors of influence (1, 2).

Research

Iguacel et al. (1) carried out a systematic review and meta-analysis to establish the effect of different diets on bone mineral density and new bone fractures. The investigation specifically looked at the difference between a vegetarian diet (no meat, fish or seafood), a vegan diet (no meat, fish, seafood, dairy products or eggs) and a diet with foodstuffs from all product groups being consumed.

Method

The researchers collected scientific publications on the subject from up to November 2017, with publications selected on children and/or adolescents and/or adults as the researched population. Publications including subjects who had already previously suffered fractures were not included in this review. In total the researchers Iguacel et al. (1) select 20 studies that met the selection criteria; these are included in the meta-analysis. Bone mineral density was measured in 15 of the 20 selected studies, and in 5 of the 20 studies the number of cases with a fracture was measured. All five studies with fracture risk as efficacy endpoint are prospective studies. The 15 studies with bone mineral density as efficacy endpoint are cross-sectional, with the exception of one longitudinal study. For bone mineral density there was the examination of the whole body (WB), the lumbar spine (LS) and the femoral neck (FN). In the original publication from Iguacel et al. (1) tables 2 and 3 show a complete summary of all study properties.

Properties of the subjects in the 20 selected studies

Total subjects 37,134
Of which data known on bone mineral density 4,003
Of which data known on fracture incidence 33,131
Average age 25 to 80 years
Gender
  • Only men:  1 of the 20 studies
  • Only women: 13 of the 20 studies
  • Men and women: 6 of the 20 studies
Country
  • Asia: 9 of the 20 studies
    Taiwan: 3, Vietnam: 2, India: 2, Korea: 1, Hong Kong 1
  • North America: 7 of the 20 studies
    United States:  6, Canada 1
  • Europe: 4 of the 20 studies
    Italy: 1, Finland 1, Slovakia: 1, United Kingdom: 1

Results

This meta-analysis suggests that both vegetarians and vegans have a lower bone mineral density measured at the lumbar spine (LS), the femoral neck (FN) and the whole body (WB). The association was more distinct among vegans than vegetarians and among subjects older than 50 years. The difference in bone mineral density at the lumbar spine and the femoral neck was also greater between vegans/vegetarians versus omnivores in Western subjects compared with Asian subjects. This difference between Europeans and Asians for bone mineral density of the whole body could not be measured by the researchers, because only one Asian study was available and the researchers deemed this insufficient to determine associations.

Difference in bone mineral density, vegans and vegetarians versus omnivores*

Vegan Vegetarian
Bone mineral density – Lumbar spine -6.3% -2.3%
Bone mineral density – Femoral neck -3.3% -1.9%
Bone mineral density – Whole body -6.0% -4.0%

Source: Iguacel et al. (1)
*Calculations based on statistical data Iguacel et al. (1)

The researchers also looked at fracture incidence. In this investigation vegans had significantly more fractures than omnivores. No significant effect was found among vegetarians versus omnivores. This association was also stronger among men and Asian subjects.

Discussion

The researchers Iguacel et al. (1) reflected comprehensively on the results in the discussion of the publication. According to the researchers the lower bone mineral density found among vegans/vegetarians corresponds with an increased fracture risk found among vegans in comparison with omnivores. The researchers state that vegans probably have a lower intake of certain nutrients such as calcium, high quality proteins, vitamin B12, vitamin D and retinol that are only found in larger quantities or exclusively in animal products. This can have an effect on bone health, according to the researchers.

The subgroup analyses suggested that people older than 50 years suffer a greater effect of a vegan diet on bone mineral density. This is explained by the researchers by bone mineral density decreasing as the person becomes older, and it may be the case that this population has already had a vegan diet for a longer time that can strengthen the effect. The subgroup analysis also raised the suggestion that the effect of a vegan diet on bone mineral density is greater among the Western population than Asians. A possible explanation mentioned by the researchers: Asians generally have shorter but thicker and denser bones than Western people. As a result, it is possible that the diet has a greater effect on bone mineral density in the Western population in comparison with Asians. Asians and the Western population also have different diets, being a possible second explanation mentioned by the researchers.

Lifestyle and diet

Various lifestyle factors such as physical activity, weight, alcohol use, medicine use and diet have an influence on bone health (2). This is also mentioned by Iguacel et al. (1). According to the researchers it is possible that associations in the meta-analysis between diet and bone mineral density are influenced by lifestyle factors. They state that vegetarians and vegans usually have a healthier lifestyle such as with more physical activity, less smoking and less alcohol and caffeine use than people with a diet without restrictions.

It is also known that substances including protein, calcium, vitamin D and phosphorous make a contribution to the preservation of the bone mass. The researchers therefore also mention that the quality of a diet can be an important factor having an effect on the findings in the meta-analysis. Only one of the 20 studies takes this into consideration. In this study the vegan diet supplied sufficient nutrients in conformity with the dietary recommendations. Hence no difference was found between a diet with animal products and a vegetarian or vegan diet. The researchers therefore see it as important that either a vegetarian or vegan diet is planned in the correct way and includes sufficient nutrients.

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