Calcium Provision in the Plant-Based Diet – Practical Advice and Tips

Calcium is an indispensable macronutrient required for the correct functioning of the body. It is primarily a building material (99% of calcium is found in bones, teeth, and nails), but a certain amount also plays a crucial role in other processes. These include: transmission of nerve signals, enabling a person to maintain balance, contraction of muscles, including the heart, activation and deactivation of enzymes such as lipases and rennin responsible for digesting fats and proteins, regulation of hormone function, particularly the parathyroid hormone produced by the parathyroid glands, and the blood clotting process and regulation of its pressure.

The requirement for calcium provision undergoes changes with age and increases during childhood and adolescence due to intense bone development and growth. In adulthood, it is intended to maintain appropriate bone mass. As age advances, the process of bone degradation accelerates, while the rebuilding of this tissue is less efficient. This is a natural process, leading to an increase in the need for calcium in older individuals. An adequate amount of this element supports the bone formation process and aids in maintaining bone mass at a constant level. In women, the onset of menopause also impacts bone metabolism, accelerating the process of bone degradation, hence their requirement for calcium increases faster than in men. Current recommendations for calcium intake are based on RDA values, i.e., recommended daily allowance (M. Jarosz et al. 2020).

The primary sources of calcium in the diet are mainly animal products such as milk and dairy products, but also fish consumed with bones (e.g. herrings, sardines) and eggs. Among the calcium-rich vegetable products, in particular, certain green vegetables (garlic, broccoli, parsley leaves, cabbage, yogurt) are listed (beans, soybeans, edamame beans), as well as seeds and nuts (sesame, almonds, poppy seeds, Brazil nuts, sunflower seeds). Mineral water is also a source of calcium, especially the highly mineralized one. However, the main problem is the difference in the bioavailability of calcium – this means that only a part of the element contained in each consumed product is absorbed. The percentage that is absorbed depends on many factors. The absorption of calcium is positively influenced by the presence of lactose, some amino acids (components of proteins), vitamin D, potassium, magnesium, and vitamins C and K. However, a negative influence can come from an excessive intake of phosphorus (these nutrients should be present in a ratio of 1:1 and if one predominates, this occurs at the expense of the other), sodium, fat, and fiber, as well as some anti-nutrients (phytates and oxalates) contained primarily in plant products. Furthermore, the absorption of calcium is reduced by the intake of caffeine and alcohol. The bioavailability of calcium from plant products varies, with the highest value (about 40–50%) for green vegetables with low oxalate content (those listed above), while lower bioavailability (15–20%) is characteristic for legumes, seeds, and nuts, as well as some fruits (oranges and figs). However, there is still another group of products that have not been mentioned before, namely milk substitutes. These are characterized by a calcium availability of 25–30%, which is a value similar to the availability of calcium from milk. However, plant-based drinks and other processed products are not naturally a good source of calcium, so it is important that they are fortified with this nutrient. In this way, the amount of calcium actually entering the body can be similar to the amount from milk.

Available data indicates that a deficiency in calcium intake is more prevalent among vegans than vegetarians. In the EPIC study published in 2007, one of the largest evaluations of the nutritional quality of diets used by individuals with different dietary patterns, it was found that nearly half of vegans consumed less than 525 mg of calcium per day, which increased the risk of bone fractures due to insufficient mineralization, while in the group of vegetarians, they represented less than 6% (P.S.B. et al. 2007). In a study conducted in 2016, the situation improved slightly. Vegans still consumed less calcium than individuals on a traditional diet (by about 25%), but the intake of this nutrient in the group of vegetarians was only 4% lower in comparison to individuals consuming meat. The average calcium content in the diet of the participants increased to 848 mg per day. In this case, particular attention is drawn to the consumption of calcium-fortified products, which constituted a source of 1/3 of the daily calcium requirement for vegans (J. G. Sobiecki et al. 2016). Similar results were obtained in a large study AHS-2 conducted among Seventh-Day Adventists, whose religion encourages them to abstain from meat and animal products. In these studies, vegans consumed about 20% less calcium than vegetarians, i.e., 933 and 1145 mg per day (G. Segovia-Siapco, J. Sabaté 2019).

Excessive calcium consumption can have negative consequences, such as the formation of kidney stones, disruptions to heart and muscle functioning, and difficulty in absorbing other components. However, in a plant-based diet, calcium deficiency is often observed, with no clinical symptoms. The consequences of calcium deficiency usually only become apparent after many years. In children, calcium deficiency can lead to rickets, a disease characterized by insufficient bone mineralization, leading to bone weakening and increased susceptibility to fractures. In adults, chronic calcium deficiency can lead to reduced bone mineral density, leading to osteopenia and its more advanced form, osteoporosis. Calcium deficiency can also lead to osteomalacia, a disease characterized by insufficient deposition of calcium in the bones, leading to their deformation. Calcium deficiency can also lead to disruptions in the nervous and muscular systems, including tetany.

As confirmed by the data presented above, calcium can be a problematic component in the plant diet, especially for vegans who do not consume dairy products. However, this does not mean that adequate calcium intake is not possible. The richest plant source of calcium is leafy vegetables, however, their consumption in sufficient quantities to meet the body's needs for this micronutrient would be problematic due to their low weight. However, it is essential to take them into account when planning meals, adding them to vegetable salads, vegetable pastes, fruit-based coconuts, and other vegetable-based dishes. Another way to increase calcium intake is to include legumes in the diet, which can be consumed not only once a day but also in several meals. In addition to calcium, they also provide many other valuable nutrients. A particularly important source of calcium are plant-based drinks, which should be enriched with this element. When purchasing plant-based products, it is essential to check whether they are enriched with calcium, as not all products are enriched. Currently, there are products on the market that are enriched with calcium, but not all products are enriched. In addition, highly mineralized water can also be a good source of calcium, which can contain up to 299 mg of calcium per liter. To increase the absorption of calcium in the body, it is advisable not to take iron supplements together with meals rich in this element. It is also recommended to avoid drinking caffeinated beverages (coffee, tea) during meals and to ensure an adequate level of vitamin D3, especially through the use of appropriate supplementation.