What is calcium?

The chemical element calcium is a key component of most plants and animals. A soft, silvery-white metal, calcium is never found in its pure form in nature since it easily forms compounds by reacting with oxygen and water. This naturally occurring element is the most abundant mineral in the human body and is vital to human health.

 

Functions of calcium

While it is well known that Calcium is an essential nutrient that keeps our bones and teeth healthy, it also plays an important role in our muscles, nerve transmission, blood clotting, hormone secretion, and other functions. 99% of the calcium in our body is found in our bones and teeth, while the remaining 1% is in our bloodstream and other tissues. Since some of the calcium in our bloodstream – which is absorbed from the bones – is lost through sweat, urine, and faeces, and because the body cannot produce additional calcium, we must consume sufficient calcium through food sources. Calcium plays a central role in the vital process of rejuvenating our bones, which continues throughout our life.^[1]Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium (2011): Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press (US) Available … Continue reading

 

Daily calcium requirements

While the recommendations for calcium intake vary considerably between regions, the following daily doses are recommended for people on a Western diet:^[2]WHO & FAO (2004): Vitamin and mineral requirements in human nutrition. Bangkok; 2004. Available from: http://apps.who.int/iris/bitstream/10665/42716/1/9241546123.pdf … Continue reading

• Adults: 700 mg
• Infants: 525 mg
• Children, aged 1 to 3: 350 mg
• Children, aged 4 to 6: 450 mg
• Children, aged 7 to 10: 550 mg
• Adolescent girls: 800 mg
• Adolescent boys: 1,000 mg
• Breastfeeding mothers: 1,250 mg
• Postmenopausal women: 1,200 mg

 

Symptoms of calcium deficiency

A lack of calcium in our diet is a risk factor for osteoporosis (weakness of the bones), which leads to a higher risk of fracture. Osteoporosis occurs because when we do not get enough calcium from our diet, it is reabsorbed from our bones, which act as a reservoir of calcium in our body.^[3]Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium (2011): Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press (US) Available … Continue reading This means that getting enough calcium through food is extremely important. Low calcium levels can directly affect bone health and the variety of functions that calcium performs in the body.

 

Health effects of excessive calcium intake

While low calcium intake can lead to osteoporosis, an excessive intake of calcium (hypercalcaemia) can result in other health problems, including poor kidney function, tissue calcification, and constipation.^[4]Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium (2011): Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press (US) Available … Continue reading However, unless one consumes high amounts of dairy products or calcium supplements, developing hypercalcaemia is rare. The maximum recommended intake for adults between the ages of 19 and 50 is 2,500 mg of calcium per day, for both men and women.^[5]Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium (2011): Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press (US) Available … Continue reading

 

Foods rich in calcium

While dairy products are often considered to be the main source of calcium in the West, sufficient quantities of calcium are also found in many plant-based sources. In fact, there are numerous reasons for favouring calcium from plants: dairy products are not just a source of calcium, but are also one of the top sources of saturated fat,^[6]Westhoek H., J.P. Lesschen, T. Rood et al. (2014): Food choices, health and environment: effects of cutting Europe’s meat and dairy intake. Glob Environ Chang. Elsevier Ltd; 2014;26(1):196–205. as well as a source of dietary cholesterol, sodium, and trans fats.

Additionally, there is little evidence that dairy consumption can protect our bones^[7]Thorning T.K., A. Raben, T. Tholstrup, et al. (2016): Milk and dairy products: good or bad for human health? An assessment of the totality of scientific evidence. Food Nutr Res. 2016;60:32527. … Continue reading – in fact, a Swedish study has shown that milk consumption may actually increase the risk of hip fracture by 9%.^[8]Michaelsson K., A. Wolk, S. Langenskiold et al. (2014): Milk intake and risk of mortality and fractures in women and men: cohort studies. BMJ. 2014;349(1756–1833 (Electronic):g6015. Available at … Continue reading Hence, dairy products are far from being a healthy source of calcium.

In contrast, plant sources of calcium do not come with any health risks if consumed in moderate quantities. Chinese cabbage, kale, broccoli, collards, mustard greens, calcium-set tofu, navy beans, white beans, almonds, tahini, dried figs, and fortified products such as plant-based milk are all significant sources of calcium. (See Table 2 below for other examples.)

 

Absorption of calcium

It’s not just the amount of calcium we consume that is important but also its bioavailability – or how easily the body can absorb the calcium from a specific source. The bioavailability of calcium from plant sources depends on the extent to which oxalates or phytates are present – both inhibit the absorption of this mineral. (The exception is soya, which is rich in both of these compounds but nonetheless has a high calcium absorption rate.)^[9]Weaver, C. M., W. R. Proulx & R. Heaney (1999): Choices for achieving adequate dietary calcium with a vegetarian diet. American Journal of Clinical Nutrition. 70, p.543S–548S. Blanching, soaking, and sprouting vegetables are highly effective ways to reduce the number of oxalates and phytates in vegetables without negatively affecting the nutritional composition.^[10]Paul V., S. Verma & A. Paul (2012) Effect of cooking and processing methods on oxalate content of green leafy vegetables and pulses. Asian J Food Agro-Industry. 2012;5(4):311–4. Available at … Continue reading

 

Food	Portion (g)	Calcium content	Percentage of calcium absorption (%)	Amount of calcium absorbed per 100 g (mg)
Broccoli	100	49	61.3	30
Chinese cabbage	100	92	53.8	49
Kale	100	72	49.3	36
Cheese	100	721	32.1	231
Cow’s milk	100	125	32.1	40
Yoghurt	100	125	32.1	40
Calcium-set tofu	100	204	31.0	63
Beans	100	52	26.7	13
Sweet potatoes	100	27	22.2	6
Chinese spinach	100	408	8.36	35
Spinach	100	135	5.1	7

Table 2 – Amount of calcium in certain foods and the percentage absorption^[11]Weaver, C. M., W. R. Proulx & R. Heaney (1999): Choices for achieving adequate dietary calcium with a vegetarian diet. American Journal of Clinical Nutritionr. 70, p.543S–548S. Available at … Continue reading

 

While dairy products are often considered to be the optimal source of dietary calcium, the calcium absorption rate from these foods (with the exception of cheese) is not as high as from dark green vegetables, as shown in the table above. Compared to dairy products, you can consume more calcium in the form of dark green vegetables without overshooting your calorie goals. Additionally, the bioavailability of calcium in calcium-fortified soy milk is similar to that of cow’s milk.^[12]Zhao, Y., B. R. Martin & C. M. Weaver (2005): Calcium bioavailability of calcium carbonate fortified soymilk is equivalent to cow’s milk in young women. J. Nutr. 135, p.2379–2382. Available … Continue reading While the oxalate and phytate content of plant-based foods can reduce calcium absorption rates, plant foods are nonetheless a good source of this nutrient because they also provide other essential nutrients, and, unlike dairy products, they do not have negative side-effects if consumed in sensible amounts.

 

Calcium and vitamin D

In order for dietary calcium to be absorbed by the intestines, the presence of vitamin D is necessary. Although most people should receive an adequate supply of vitamin D from sunlight for most of the year, in winter, when the days are short and the sun is low, vitamin D deficiency can be a problem. This is of particular importance for people living in Europe, where the prevalence of vitamin D deficiency has reached concerning levels.^[13]Kevin D Cashman, K. Dowling, Z. Škrabáková, et. al. (2016): Vitamin D deficiency in Europe: pandemic?. Am J Clin Nutr. 103 (4), 1033–1044. Luckily, vitamin D can also be found in mushrooms and fortified foods such as plant milks and tofu, but consuming these foods may not suffice and vitamin D supplements may be required to boost calcium absorption during the winter months.

 

Calcium supplements

While calcium supplements can be useful in cases of extremely low calcium intake or nutritional deficiency,^[14]Gibson, P. S., M. J. Sadler & S. A. Lanham-New (2018): 3 – Authorised EU health claims for calcium and calcium with vitamin D (for low bone mineral density and risk of fractures). In: … Continue reading there are associated gastrointestinal, renal, and cardiovascular risks.^[15]Reid, I. R., S. M. Bristow & M. J. Bolland (2015): Calcium supplements: benefits and risks. J. Intern. Med. 278, p.354–368. Available at. http://www.ncbi.nlm.nih.gov/pubmed/26174589 [22.03.2018] Caution should be exercised when supplementing with doses of calcium greater than 500 mg in a single serving as it can lead to the calcification of arteries^[16]Reid, I. R. & M. J. Bolland (2012): Calcium supplements: bad for the heart? Heart. 98, p.895–896. Available at http://heart.bmj.com/content/98/12/895.long [22.03.2018] and also increases the risk of cardiovascular problems in the long-term, although this does not apply to calcium present in food.^[17]Bolland M.J., A. Avenell, J. A. Baron et al (2010): Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010 Jul 29;341:c3691. Available at … Continue reading For this reason, the intake of calcium-fortified foods containing 200-300 mg of calcium per portion (for example, commercial plant-based milk) is safe, but doses above this value should be approached with caution. When consuming plant-based milk that is calcium-fortified, the container should be well-shaken as the calcium usually sinks to the bottom.

 

Calcium supply for vegans and vegetarians

A well-balanced diet, free from animal products and rich in vegetables, fruits, and whole grains, can provide sufficient calcium to the human body with none of the health risks associated with the consumption of dairy products., Additionally, the bioavailability of plant-based calcium is often higher than that of dairy products.^[18]PCRM: Calcium and Strong Bones. Available at. http://www.pcrm.org/health/health-topics/calcium-and-strong-bones [29.03.2018] ^[19]https://nutritionfacts.org/topics/calcium/

However, it is important to ensure that the body gets a sufficient amount of vitamin D in order to optimise calcium absorption. Supplements should be taken into consideration as they offer a more controlled and more substantial quantity of vitamin D than fortified foods. To ensure healthy levels of calcium and vitamin D, and to find the right dosage for supplementation, blood tests and medical advice should be sought.

 

ProVeg tips for optimal plant-based calcium supply

• A vegan diet can provide a sufficient supply of calcium if enough plant-based calcium sources are consumed.
• Cruciferous vegetables, leafy greens, beans, and potatoes are valuable sources of calcium.
• Blanching or sprouting vegetables can decrease the presence of oxalates and phytates and thus increase the absorption of calcium.
• Plant-based sources of calcium are healthier than calcium from dairy products.
• Spend enough time in the sun and consider taking vitamin D supplements during times when sunlight is scarce in order to boost calcium absorption.