Vegan and vegetarian diets are increasingly popular these days. However, there are some concerns about their long-term impact on bone health. The effect could be due to the low intake of animal proteins, particularly dairy products—vitamin D and calcium.
The terms vegan and vegetarians are increasingly popular in western society. It is estimated that almost 3 to 5% of the US population are either vegans or vegetarians and the numbers increase (Ho-Pham et al. 2012).
Plant Proteins: Benefits and Concerns
The vegan or vegetarian practice is based on abstaining from the consumption of animal-based products, the main source of animal proteins. However, a wide array of health benefits, including the protection against several chronic diseases, such as hypertension, heart disease, type 2 diabetes, overweight, and some forms of cancers such as colorectal and prostate cancer, also attract an increasing number of western people to consuming more plant-based food and avoiding animal products.
There exist concerns as well. As the number of elderly populations has increased worldwide, reports show an increased prevalence of osteoporosis and bone fracture cases. Researchers have linked consumption of only plant-based products and avoiding animal proteins to increased association with deteriorated bone health (Tucker 2014).
However, evidence shows that bone-health concerns are primarily due to the low intakes of some nutrients such as vitamin B12, vitamin D, calcium, and n-3 fatty acids in poorly selected vegetarian or vegan diets (Appleby et al. 2016).
An EPIC (European Prospective Investigation into Cancer and Nutrition) Oxford study found higher fracture risk among vegans appeared to be a consequence of their considerably lower mean calcium intake. The prospective cohort study included a total of 7947 men and 26749 women aged 20–89 years, including 19249 meat eaters, 4901 fish eaters, 9420 vegetarians, and 1126 vegans (Appleby et al. 2007).
Consuming Plant Proteins only Detrimental to Bone Health
Researchers at the University of Helsinki investigated the mechanisms, how consuming proteins only from the plant source is detrimental to bone health. They found that partial replacement of animal protein with plant protein in the diet altered bone metabolism and decreased calcium and vitamin D intakes. The results are published in The Journal of Nutrition, January 2021 (Itkonen et al. 2020).
The investigators randomly assigned 136 adults (107 women and 29 men) to three groups in the study. One group was given a Finnish diet, containing roughly 70% animal-derived protein of total protein, while most of the plant-based protein originated from cereal products.
The second group of participants consumed a diet containing ’50/50′ animal vs. plant protein, and the third group had a diet of 30% of animal protein and 70% of plant-based protein. The intervention period was for 12 weeks.
According to the study protocol, meat and dairy products were the sources of animal proteins, which were replaced by the plant proteins of legumes, nuts, seeds, and cereal. All diets contained the same amount of fish and eggs.
After examining differences in bone formation, bone resorption and mineral metabolism markers, and nutrient intakes, the researchers found that both bone formation and resorption increased when a part of the animal protein in the diet was replaced with plant protein.
The researchers suggest that bone metabolism changes and changes in calcium and vitamin D intakes are probably caused by the low amount of dairy products and, consequently, the low amount of calcium and vitamin D consumption. Low intake of dairy products may cause a detrimental effect on bone health in the long term.
“When consuming plant-based drinks and yogurt-like products, it is essential to choose the option fortified with calcium and vitamin D. If the daily diet contains no margarine, dairy products or plant-based drinks fortified with vitamin D, and if fish is consumed less than 2-3 times per week, it’s important to ensure adequate vitamin D intake, especially in the dark season, by taking a daily vitamin D supplement.”—reads the University of Helsinki press release (Itkonen 2021).