The Best Vegan Calcium Sources

Calcium is the most important mineral in the body in terms of quantity. The human organism contains about 1–1.4 kg of calcium in the human organism, which is about 1.5 % of body weight (Leitzmann and Keller, 2013). The original source of calcium is the soil. Plants absorb it and thus are a calcium source for humans.

It is not only the calcium content of a food that counts when it comes to providing the mineral, but at least as important is its bioavailability, that means its absorption, metabolism and utilization in the body. Calcium from plant foods is often readily available due to their high mineral content. Studies have shown that high consumption of animal protein (from meat, milk and dairy products) is associated with increased urinary calcium excretion. What is behind this phenomenon and how to get enough calcium from plant-based sources is explained below.

Functions

Calcium is found in hard tissue (bones, teeth) to 99 % linked to phosphorus as a so-called hydroxyapatite salt. In this crystalline compound, it provides strength and stability to the tissues. Due to its quantitative distribution in the bones, it also represents an important calcium reservoir. The remaining 1 % of calcium is found in cells and blood plasma. There it plays a role in blood clotting, as a messenger substance for muscle contraction, and in the transmission of nerve impulses. Calcium also activates certain enzymes in metabolic processes.

Several mechanisms regulate calcium homeostasis in the blood. The two hormones parathyroid hormone and calcitonin, which act antagonistically, are particularly well known: when calcium levels fall, the parathyroid gland is stimulated to secrete parathyroid hormone, which causes calcium to be mobilized from the bones. When blood levels of the mineral rise, the antagonist calcitonin comes into play. This comes from the thyroid gland and inhibits the mobilization of calcium from the bones.

Bioavailability

Physiological factors affect the individual bioavailability of calcium. Depending on age, needs (pregnancy, lactation), and current vitamin D and calcium status, the mineral may be absorbed at different rates through the intestine.

Vitamin D is closely linked to calcium metabolism, as it ensures adequate absorption of calcium through the intestinal mucosa and influences its excretion through the kidneys as needed. The vitamin also plays a role in bone metabolism by keeping the continuous build-up and breakdown of tissue at a healthy level.

In addition, caffeine and table salt are often referred to as “calcium robbers” because an increased intake of these substances can promote calcium excretion. However, negative effects on bone metabolism are not necessarily a concern if calcium intake is adequate, because intestinal calcium absorption may increase at the same time, and the calcium in the urine is unlikely to come from bone. In individuals at increased risk for kidney stones, salt restriction may reduce stone formation (Heaney, 2002; Prezioso et al., 2015).

Comparison of Animal and Vegan Calcium Sources

Calcium also plays an important role in how your daily diet affects your body’s pH. Calcium is involved in acid-base balance and acts as a buffering agent in a state of excess acidity. It can be released from bone and buffer excess acid builders to restore acid-base balance. An acid load may be caused by a high intake of protein, especially of animal origin, and a low intake of mineral-rich foods, such as vegetables and fruits, in a very unbalanced diet. Among proteins, the two sulfur-containing amino acids methionine and cysteine play a crucial role. Increased intake of these protein building blocks promotes calcium excretion in the urine. However, in studies animal protein consumption did not lead to a negative calcium balance and an increased risk of osteoporosis because the calcium measured in the urine is unlikely to originate from bone; therefore, calcium excretion does not allow drawing conclusions about bone metabolism (Fenton et al., 2009; Fenton et al., 2011; Cao and Nielson, 2010; Nicoll and Howard, 2014).

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High fruit and vegetable consumption can counteract potential calciuria due to its potassium and magnesium content. Conscious food choices of vegan calcium sources can ensure adequate calcium bioavailability in a plant-based diet (ADA, 2009).

What to Look for in Vegan Calcium Sources

Certain inhibitors found in plant foods reduce the bioavailability of calcium. As with the absorption of other minerals, such as iron and zinc, these substances can form complexes with dissolved calcium ions, promoting their excretion and inhibiting absorption. In order to be absorbed through the intestinal mucosa, calcium and all other minerals must be present in dissolved form as charged particles (ions). Inhibitors include phytates in grains and legumes, or oxalates in green leafy vegetables (spinach, chard). Calcium absorption from vegetables low in oxalates (cabbage, pak choi, broccoli) is about 50–60 %, and can be less than 10 % from foods high in oxalates (ADA, 2009; Weaver et al., 1999). In comparison, the absorption rate from dairy products is about 30 %. The bioavailability of calcium-fortified soy milk varies depending on the calcium compound used: In studies, calcium carbonate, chloride, and sulfate were absorbed to a similar extent as calcium from cow’s milk; the availability of tricalcium phosphate is about 25 % lower, and calcium from the red algae Lithothamnium calcareum is also less well absorbed (Agnoli et al., 2017; Scholz-Ahrens et al., 2020). The chelated compound calcium bisglycinate is thought to be particularly stable and therefore readily available.

Requirements and Status

Nutrition societies recommend a daily intake of 1000 mg of calcium for adults aged 19 years and older (DGE et al., 2016; IOM, 2011; WHO/FAO, 2004). Due to differences in bioavailability, general dietary patterns may influence the individual amount needed to meet requirements.

During growth, there is an increased requirement due to the build-up of skeletal muscle. This increases with age and peaks at 1200 mg/day in adolescents between 13 and 19 years of age. Maximum bone density occurs between the ages of 25 and 30, after which there is a slow, steady decline of 0.5–1.5 % per year. This process increases to about 3.5 % per year, especially in menopausal women, due to hormonal status (Leitzmann and Keller, 2013).

On the one hand, you can have your calcium status determined by a blood test, in which a concentration between 2.1–2.6 mmol/l is considered the reference range. However, the serum concentration is not an optimal marker because it is kept constant within very narrow limits by regulatory mechanisms. If there is a deficiency, calcium is mobilized from the bone and the serum concentration remains in the normal range for a very long time. Measurement of bone mineral density can be used as an indicator of long-term calcium status. However, it also depends on many other factors, such as vitamin D intake and physical activity. A food diary can provide information on intake and thus an indication of whether the status may be critical.

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Deficiency

In children and adolescents, inadequate calcium intake results in poor bone mineralization, which may be associated with short stature or dental development problems. In later life, low bone density is called osteopenia or, pathologically, osteoporosis (bone loss). This increases the risk of fractures, which can be life-threatening in old age. In addition to adequate calcium intake, other factors play an important role in maintaining strong, healthy bones. These include the vitamin D status (primarily through endogenous synthesis stimulated by UV-B radiation from sunlight), other nutrients (for example vitamin K), antioxidants, sufficient exercise, and adequate protein intake.

Occurrence

There is a variety of vegan calcium sources. These include green (leafy) vegetables such as kale, arugula, pak choi, broccoli, collard greens, and spinach. Wild herbs, such as dandelion, can help provide calcium. You can use them in salads or green smoothies. Dried fruits, almonds, hazelnuts and Brazil nuts, pseudo grains (amaranth, quinoa), sesame or soy and products made from them are also good vegan calcium sources. Chickpeas, chia seeds, hemp seeds, and poppy seeds also contain significant amounts. Mineral waters with > 40 mg calcium/100 ml can be used to meet your needs (Leitzmann et al., 2018). Table 1 shows the calcium content of some vegan calcium sources per 100 g. Note that nori leaves, for example, have a high calcium content, but in the amount usually consumed, they may contribute only marginally to the intake.

Table 1: Calcium Content of Plant Foods (Elmadfa et al., 2007; BLS)

Status on a Vegan Diet

In studies, the calcium intake of vegans has been found to be lower than that of vegetarians and mixed-food eaters (Larsson and Johansson, 2002; Davey et al., 2003; Ströhle et al., 2011; ADA, 2009).

With regard to bone mineral density, there are differences within the vegan population. In one study, vegans with a very low calcium intake of less than 500 mg/day had low bone density, whereas in vegans with a calcium intake of more than 500 mg daily, bone density was comparable to that of vegetarians and mixed-food eaters (Appleby et al., 2007).

Conclusion

As a component of bone tissue, calcium is an important dietary mineral. You can achieve an adequate supply of calcium through a plant-based diet with the following measure: Some fruit and vegetables are good vegan calcium sources. Soaking legumes and nuts reduces the phytate content, thus eliminating the inhibiting effect on calcium absorption. Oxalate is only found in significant concentrations in some vegetables like spinach and chard. Cabbage, broccoli, and pak choi are low in oxalate and can therefore be good vegan sources of calcium. Calcium-rich mineral water can also provide calcium for vegans. Children, pregnant and breastfeeding women, and older people should be especially careful about their calcium intake.