Calcium in the human body is a matter of balance. 99% of our calcium is stored in the bones and teeth. The rest resides in the blood and soft tissues for immediate accessibility. Blood calcium plays important roles in body processes including;
Carrying messages amongst cells
Communication between the brain and the rest of the body
Contractions in the skeletal muscles and, more importantly, in the heart
Maintenance of blood pressure
Regulation of immune cell function
The human body maintains careful control of the amount of calcium in the bloodstream. If blood levels fall too low, calcium absorption from food increases, less calcium is excreted through the urine and, if necessary, some calcium is released from the bone into the blood. Three hormones play roles in calcium balance. These are parathyroid hormone, calcitonin and Vitamin D (1).
Recommended Daily Amounts of Calcium
If you look up the recommended daily allowance (RDA) for calcium you will likely find that it is somewhere between 1000 mg and 1300 mg for adults (2). But in actuality the daily required amount varies with the diet you are eating. Our calcium requirement is the amount needed to replace the amount of calcium lost. Diets high in animal protein tend to increase calcium excretion. However, eating a whole-food plant-based diet is associated with lower rates of calcium excretion so that calcium intake can be much lower. A 2007 study looked at the amount of calcium necessary to keep calcium balanced. In those eating nutritionally adequate diets low in sodium and protein the daily calcium requirement may be as low as 500 mg to 741 mg (3). Some countries are now informing their residents of this reduced recommendation. The official calcium requirement for British adults is now set at 700 mg daily (4) and Nordic country authorities recommend 800 mg daily (5).
Calcium is a mineral and it is one of the most abundant minerals on earth, making up over 4% of the earth’s crust. Calcium in the soil gets taken up into the roots of plants and transfers into animals when they eat the plants. But it is not necessary for humans to use cows as their “middle-man” calcium source. Eating a whole-food plant-based diet that includes a variety of plant material will supply more than enough calcium to meet dietary needs.
Interestingly, our organs can adjust if the calcium in our food is present in low quantities. The intestines become more efficient at absorbing calcium and the kidneys conserve it by sending less out of the body through the urine. On the other hand, if our diet is overflowing with calcium, the intestines will block its absorption and the kidneys will eliminate more. So our body works with our environment to make sure we absorb just the right amount of calcium (6).
Here is another factor to consider. Just because there is calcium in our diet doesn’t mean that our body will actually take it in. Different food sources of calcium have different rates of absorption. For instance, only about 30% of the calcium in milk is absorbable. Some vegetables, such as Chinese cabbage greens, are very high in calcium and about 54% of it is absorbable in our bodies. Two cups of broccoli (60% absorbable) or 1 ½ cups of kale (50% absorbable) will each supply about the same amount of calcium as 1 cup of milk due to their different absorption rates (7).
Barriers to calcium absorption
Some food components cause us to lose calcium (8).
Sodium: For each 1000 mg of sodium (2500 mg of table salt, ½ tsp.) that is eliminated by our kidneys, 40 to 60 mg of calcium is excreted along with it.
Protein: Higher protein in the diet, especially protein from animal-sourced foods, increases the urinary excretion of calcium. For example, if you double your protein intake you increase the loss of calcium in the urine by 50%. If you’re getting your calcium from dairy products, you will lose about 1/3 of the calcium coming from milk and 2/3 of the calcium from cheese in your urine because of the higher level of protein in dairy products.
Caffeine: The diuretic effect of caffeine takes calcium out of the body too.
On the other hand, plants, especially leafy green vegetables and legumes, provide lots of calcium that is highly absorbable and doesn’t cause extra calcium loss.
Calcium supplements are not the way to go. In fact studies show that, though they are being taken to reduce fracture risk, that outcome is not at all certain. Conversely, calcium supplements increase risks of cardiovascular disease, strokes, kidney stones and GI distress (9,10,11,12,13).
Results from multiple randomized controlled trials show no reduction in hip fracture risk with calcium supplementation. In fact, increased risk is possible (14).
A 2010 meta-analysis showed that calcium from supplements, but not calcium present in food, increases the risk of cardiovascular problems in the long-term (10).
A 2014 randomized, double-blind placebo-controlled study of over 36,000 postmenopausal women not only revealed a higher risk of myocardial infarction and stroke with calcium supplements but also that milk consumption may increase risk of hip fracture by 9% (15).
An earlier 2013 randomized controlled study showed increased cardiovascular risk from calcium supplements across a wide variety of patient groups (9).
In addition, calcium supplements with doses greater than 500 mg at one time can lead to calcification of the arteries with resultant increased cardiovascular mortality (11).
What if all you eat are plants?
A recent study compared the bone mineral density of long-term vegans with that of omnivores to find that even though vegans have much lower intakes of calcium and protein, there is no appreciable difference in their bone density (16).
Non-Dairy sources of calcium
Although most plant-based foods contain some calcium, the healthiest sources are green leafy vegetables and legumes. These plants contain highly absorbable calcium (with the exceptions of spinach, rhubarb, beet greens or swiss chard whose high levels of oxalates lower calcium absorption through the formation of insoluble calcium oxalate salts (8).)
There is more than 150 mg of calcium in a serving of baked beans.
Some herbs are concentrated sources of calcium. For example, 2 tablespoons of dried ground basil have almost the same amount of calcium as one cup of 1% milk (220 milligrams compared to 240 milligrams) (17).
Calcium in selected foods (18,19)
Note: 250 ml/gm is slightly larger than 1 cup; 100 ml/gm is slightly smaller than ½ cup; 30 gm is about 2 tablespoonsful
250 ml fortified soy milk 350 mg calcium
100 gm tofu 200 mg calcium
Leafy greens (100 gm of leafy greens are about 1 ½ cups of moderately packed leaves)
100 gm raw kale 250 mg calcium
100 gm cooked kale 150 mg calcium
100 gm raw arugula 162 mg calcium
100 gm raw collard greens 232 mg calcium
100 gm cooked collard greens 210 mg calcium
100 gm raw turnip greens 190 mg calcium
100 gm cooked turnip greens 152 mg calcium
100 gm raw dandelion greens 187 mg calcium
100 gm cooked dandelion greens 140 mg calcium
100 gm cooked mustard greens 158 mg calcium
250 gm cooked soybeans 360 mg calcium
250 gm cooked navy beans 185 gm calcium
250 gm cooked kidney beans 165 gm calcium
250 gm cooked edemame 158 mg calcium
250 gm home-prepared baked beans 153 mg calcium
250 gm cooked black beans 138 gm calcium
250 gm cooked chick peas 122 mg calcium
250 gm cooked lentils 120 mg calcium
100 gm hummus (chickpeas) 49 mg calcium
Nuts and Seeds
30 gm sesame seeds (tahini) 269 mg calcium
30 gm chia seeds 180 mg calcium
30 gm flaxseeds 71 mg calcium
100 gm roasted almonds 291 mg calcium
100 gm almond butter 172 mg calcium
100 gm roasted peanuts 86 mg calcium
100 gm peanut butter 72 mg calcium
1 tbsp dried oregano 90 mg calcium
1 tbsp dried thyme 80 mg calcium
2 tbsp dried marjoram 60 mg calcium
1 tbsp dried parsley 22 mg calcium
25 gm raw garlic 45 mg calcium
100 gm raw or cooked onions 72 mg calcium
250 gm broccoli raab (rapini) 300 mg calcium
250 gm snap peas 150 g calcium
250 gm broccoli 127 mg calcium
250 gm potatoes with skin 120 mg calcium
250 gm butternut squash 120 mg calcium
250 gm raw red cabbage 113 mg calcium
250 gm acorn squash 110 mg calcium
250 gm raw celery 100 mg calcium
250 gm red or green sweet peppers 103 mg calcium
250 gm sweet potato 95 mg calcium
250 gm parsnips 93 mg calcium
250 gm Brussels sprout 90 mg calcium
250 gm raw carrots 90 mg calcium
250 gm cooked carrots 75 mg calcium
250 gm canned tomatoes 85 mg calcium
250 gm kimchi cabbage 82 mg calcium
250 gm turnips cooked 82 mg calcium
250 gm cauliflower cooked 80 mg calcium
250 gm Chinese cabbage 80 mg calcium
250 gm asparagus 70 mg calcium
100 gm orange 80 gm calcium
100 gm blackberries 30 mg calcium
100 gm raspberries 24 mg calcium
100 gm blueberries 19 mg calcium
100 gm strawberries 16 mg calcium
100 gm cherries 16 mg calcium
100 gm pineapple 16 mg calcium
100 gm grapefruit 15 mg calcium
100 gm avocado 12 mg calcium
100 gm pears 11 mg calcium
100 gm grapes 10 mg calcium
100 gm plums 10 mg calcium
100 gm melon 9 mg calcium
100 gm figs 162 mg calcium
100 gm pitted prunes 72 gm calcium
100 gm raisins 64 gm calcium
100 gm dates 64 gm calcium
100 gm dried apricots 15 mg calcium
Don’t forget your Vitamin D
Vitamin D and calcium work together to maintain calcium balance. Vitamin D helps ensure that the body absorbs and retains calcium and phosphorus, both critical minerals for our health. If we have exposure to enough sunlight, our bodies can produce all the Vitamin D we need. However, Canadians and others who live at northern latitudes must endure a long winter season when they are forced to spend much of their time indoors. Additionally, the sun’s rays in these latitudes in the winter season meet the earth at low angles, making them very weak. Under these conditions we are able to produce only very little if any natural Vitamin D. Luckily this is easy to remedy. Simply take a daily Vitamin D supplement of 800 IU to 1000 IU daily for adults (400 IU for children) from September to June. If you want to ensure you’re getting enough Vitamin D, ask your doctor to check your Vitamin D level to confirm that it is within the healthy range (20,2).
It is time to re-examine our ideas about calcium. We need not depend on cow’s milk, a food that evolved to meet the tremendous growth requirements of cattle, especially one that brings with it detrimental constituents such as animal protein, saturated fat and milk sugars as well as harmful contaminants that contribute to the ill health of our modern society. Calcium is readily available, and often more absorbable, in many whole plant-based foods. In addition, plant-based foods contain an abundance of healthy nutrients that animal-based foods simply do not have such as fiber, antioxidants and other protective phytochemicals. You can safely and healthfully help reduce your risk of developing a host of chronic diseases by limiting milk products from your diet and concentrating on whole plant foods (21).
1 Goodman, H. Maurice. Basic Medical Endocrinology; 4th Edition, 2009. Academic Press.
3 Hunt, C.D., Johnson, L.K. Calcium requirements: new estimations for men and women by cross-sectional statistical analyses of calcium balance data from metabolic studies. Am J Clin Nutr. Oct 2007; 86(4): 1054-1063.
5 Michaëlsson K. Calcium supplements do not prevent fractures. BMJ. 2015;351:h4825.
6 O’Brien, K.O., Abrams, S.A., Liang, L.K., Ellis, K.J., Gagel, R.F. Increased efficiency of calcium absorption during short periods of inadequate calcium intake in girls. Am J Clin Nutr. 1996 Apr; 63(4):579-583.
7 Weaver, C. M., Proulx, W.R., Heaney, R. Choices for achieving adequate dietary calcium with a vegetarian diet. American Journal of Clinical Nutrition 1999; 70: 543S–548S.
9 Radford, L.T., Bolland, M.J., Gamble, G.D., Grey, A., Reid, I.R. Subgroup analysis for the risk of cardiovascular disease with calcium supplements. Bonekey Rep. 2013; 2: 293.
10 Bolland, M.J., Avenell, A., Baron, J.A. et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010 Jul 29;341:c3691.
11 Reid, I.R., Bolland, M.J. Calcium supplements: bad for the heart? Heart 2012; 98:895–896.
14 Bischoff-Ferrari, H.A., Dawson-Hughes, B., Baron, J.A., et al. Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomized controlled trials. Am J Clin Nutr. 2007; 86:1780–1790.
15 Michaëlsson, K., Wolk, A., Langenskiöld, S., Basu, S., Lemming, E.W., Melhus, H., Byberg, L. Milk intake and risk of mortality and fractures in women and men: cohort studies. BMJ 2014; 349
16 Knurick, J.R., Johnston, C.S., Wherry, S.J., Aguayo, I. Comparison of Correlates of Bone Mineral Density in Individuals Adhering to Lacto-Ovo, Vegan, or Omnivore Diets: A Cross-Sectional Investigation. Nutrients. 2015 May; 7(5): 3416–3426.
21 Lanou, A.J. Should dairy be recommended as part of a healthy vegetarian diet? Counterpoint. Am J Clin Nutr. May 2009;89(5):1638S-1642S.