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Vitamin D and Calcium Supplementation Protect against Fractures in Vegan Women

Woman drinking soymilk

While there is evidence indicating vegetarian diets reduce the risk of chronic diseases such as diabetes,1 cardiovascular diseases,2 and certain cancers,3 there are also concerns that a vegetarian, and especially a vegan, diet increases fracture risk.4 However, new research shows that vitamin D and calcium supplementation eliminates the association between vegan diet and fracture risk.5 Fortified soymilks and calcium-set tofu, can be excellent sources of well-absorbed calcium. Fortified soymilks are also a good source of vitamin D.

In a previous blog post, I highlighted a meta-analysis of 9 studies which found that bone mineral density (BMD) was approximately 4% lower in vegetarians than in omnivores at both the femoral neck and the lumbar spine.6 Vegan BMD was lower than that of lacto-ovo-vegetarians. Nevertheless, the authors of this analysis concluded that the lower BMD was clinically insignificant. A decade later, a systematic review and meta-analysis that included 20 studies and 37,134 participants aligned with the BMD findings, however, this study found vegans also had higher fracture rates.7

More importantly, the results of the EPIC-Oxford study found that vegans had a 43% higher risk of fractures overall compared to nonvegetarians.8 The biggest difference was for hip fractures; vegans were more than twice as likely as people who ate meat to break their hip. However, sub-analysis of the results of this British study revealed that risk for all fractures combined was increased among vegan women but not among vegan men and only among individuals with a body mass index (BMI) below 22.5. For perspective, the average BMI among nonvegetarians and vegans in the Adventist Health Study-2 was 28.3 and 24.1, respectively.9 Therefore, relatively few vegans are likely to be at increased fracture risk.

In a 2014 commentary, Tucker noted that vegetarian diets have been shown to contain lower amounts of calcium, vitamin D, vitamin B-12, protein, and omega-3 fatty acids, all of which have important roles in maintaining bone health.10 While this may be true, researchers at Loma Linda University have identified calcium and vitamin D as the two nutrients responsible for the increased vegan hip fracture risk.5

Their conclusion was based on the results of the Adventist Health Study 2, a prospective cohort study which enrolled participants between 2002 and 2007. The study identified 679 incident hip fractures during 249,186 person-years of follow-up. In multivariable models, including adjustment for calcium and vitamin D supplementation, female vegans had a statistically significant 55% higher risk of hip fracture than nonvegetarians, whereas there was no association between diet pattern and hip fracture risk in men. These results align well with the above cited results from the EPIC-Oxford study.8 Importantly however, vegans taking both vitamin D and calcium supplements were at no greater risk of hip fracture than were subjects with other dietary patterns including non-vegetarians. The mean dosage of each supplement differed little by pattern: ∼660mg Ca/day (adult RDA, 1,000mg) and ∼13.5μg vitamin D/day (adult RDA, 15μg).

The protective effects of vitamin D and calcium supplementation is especially notable considering the debate about the benefits of these nutrients for fracture prevention.11 It does seem prudent to recommend that vegan women be sure to meet their requirements for vitamin D and calcium and, if having difficulty consistently doing so, to consider the routine use of fortified foods and/or supplements.

References

  1. Qian F, Liu G, Hu FB, et al. Association Between Plant-Based Dietary Patterns and Risk of Type 2 Diabetes: A Systematic Review and Meta-analysis. JAMA internal medicine. 2019;179:1335-44.
  2. Benatar JR, Stewart RAH. Cardiometabolic risk factors in vegans; A meta-analysis of observational studies. PloS one. 2018;13:e0209086.
  3. Dinu M, Abbate R, Gensini GF, et al. Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies. Crit Rev Food Sci Nutr. 2017;57:3640-9.
  4. New SA. Do vegetarians have a normal bone mass? Osteoporos Int. 2004;15:679-88.
  5. Thorpe DL, Beeson WL, Knutsen R, et al. Dietary patterns and hip fracture in the Adventist Health Study 2: combined vitamin D and calcium supplementation mitigate increased hip fracture risk among vegans. Am J Clin Nutr. 2021.
  6. Ho-Pham LT, Nguyen ND, Nguyen TV. Effect of vegetarian diets on bone mineral density: a Bayesian meta-analysis. Am J Clin Nutr. 2009;90:943-50.
  7. Iguacel I, Miguel-Berges ML, Gomez-Bruton A, et al. Veganism, vegetarianism, bone mineral density, and fracture risk: a systematic review and meta-analysis. Nutr Rev. 2019;77:1-18.
  8. Tong TYN, Appleby PN, Armstrong MEG, et al. Vegetarian and vegan diets and risks of total and site-specific fractures: results from the prospective EPIC-Oxford study. BMC Med. 2020;18:353.
  9. Orlich MJ, Singh PN, Sabate J, et al. Vegetarian dietary patterns and mortality in Adventist Health Study 2. JAMA internal medicine. 2013;173:1230-8.
  10. Tucker KL. Vegetarian diets and bone status. Am J Clin Nutr. 2014;100 Suppl 1:329S-35S.
  11. Kahwati LC, Weber RP, Pan H, et al. Vitamin D, Calcium, or Combined Supplementation for the Primary Prevention of Fractures in Community-Dwelling Adults: Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA. 2018;319:1600-12.
Dr. Mark Messina

Author Dr. Mark Messina

PhD in Nutrition, Executive Director, Soy Nutrition Institute. Expert in soyfoods and isoflavones.

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