Calcium is one of the 118 chemical elements which make up all known matter. It is incredibly common, being the 5th most abundant element in earth. It is also the 5th mots abundant element in the human body and the most abundant mineral found in the human body.
Calcium is highly reactive, which is why it is used in so many processes ranging from cement production to making alloys. As an essential nutrient in the human body, calcium mostly serves for structural support with about 99% of the body’s calcium found in our bones and teeth. However, the reactive properties of calcium are crucial for numerous bodily processes. The remaining 1% of our body’s calcium is used for functions such as:
- Helping to dilate and constrict blood vessels
- Constricting and relaxing muscle cells, thus allowing muscle movement
- Transmitting nerve impulses
- Stabilizing proteins and enzymes so they may function
- Releasing hormones
Recommended Calcium Intake
Calcium is needed for all living organisms to function. The Institute of Medicine puts recommends that humans get the following amounts of calcium daily:
Do Vegetarians Require Less Calcium?
Some sources have claimed that vegetarians require less calcium daily than meat eaters. These claims are based on the idea that vegetarians consume less protein. Calcium is used to neutralize protein oxidation in the body, thus high amounts of protein can deplete calcium storages.
While it is true that most vegetarians are eating less protein than meat eaters, there is no evidence which shows vegetarians require less calcium than meat eaters. Vegetarians putting faith in these claims could be subjecting themselves to a calcium deficiency. Even if the claims do prove to be true, vegetarians should still play it safe and follow the recommended guidelines for calcium.
Dairy vs. Vegan Sources of Calcium
Calcium is most notoriously found in milk and other dairy products such as yogurt and cheese. These animal sources of calcium have a high bioavailability, meaning that the calcium is easily absorbed by the human body.
Calcium is also abundantly found in many vegan foods, such as dark leafy greens and beans. However, many vegan sources of calcium have a much lower bioavailability than dairy. This is because many vegetables contain high amounts of chemicals which inhibit calcium absorption. For example, spinach contains oxalic acid which is very powerful in blocking calcium absorption. Phytic acid, which is found in bran, seeds, and legumes, also blocks calcium absorption. Do note, however, that certain other chemicals may neutralize these anti-calcium chemicals. For example, the enzyme phytase which is found in yeast (and thus in many breads) breaks down phytic acid.
It is important for vegans and vegetarians to realize that the actual amount of calcium listed in foods may not represent the amount which their body will absorb.
For example: A ½ cup serving of pinto beans contains 45 mg of calcium compared to 300mg in a 8oz serving of milk. However, because this calcium has a lower bioavailability than milk, it would take 8.1 servings of pinto beans (not 6 2/3) to get the same amount of calcium as the milk provides.
The Oregon State University Micronutrient Information Center has a table (taken from the American Journal of Clinical Nutrition) which shows the amount of servings of plant sources of calcium that one would need to consume to get the same amount of calcium available in a glass of milk.
Servings needed to equal the absorbable calcium in 8 oz of milk
|Milk or Yogurt||8 ounces||
|Red beans||1/2 cup, cooked||
|White beans||1/2 cup, cooked||
|Tofu, w/ calcium||1/2 cup||
|Bok choy||1/2 cup, cooked||
|Kale||1/2 cup, cooked||
|Broccoli||1/2 cup, cooked||
|Spinach||1/2 cup, cooked||
|Rhubarb||1/2 cup, cooked||
|Fruit punch with calcium citrate malate||8 ounces||
From this table, you can see that some vegan foods with high amounts of calcium, like spinach and rhubarb, are poor sources of calcium because of their low bioavailability. However, some vegan foods, like kale and bok choy, have even higher bioavailability of calcium than milk and thus are good vegan sources of calcium.
Absorption of Calcium
In general, humans can absorb about 30% of calcium from foods. However, there are numerous factors which can affect the absorption of calcium, including:
- Oxalic acid and phytic acid: Typically found in many plant-based foods like legumes
- Amount of Calcium Consumed: If high amounts of calcium are consumed at once, then less will be absorbed.
- Age: Infants and children are better able to absorb calcium than adults (approximately 3-4 times better).
- Menopause: Low levels of estrogen, which is common in post-menopausal women, is associated with decreased level of calcium absorption.
- Vitamin D: Vitamin D significantly improves calcium absorption.
- Stomach Acid: Stomach acid is needed to help the body absorb calcium. People with low levels of stomach acid, such as the elderly, will not absorb calcium as efficiently.
- Caffeine: High levels of caffeine, such as found in coffee or tea, can decrease calcium absorption.
- Alcohol: Alcohol can decrease calcium absorption and also decreases vitamin D absorption.
***One positive thing to note is that cooking foods does not significantly impact its calcium content.
Symptoms of Calcium Deficiency
People with a calcium deficiency typically do not have any symptoms. However, as the deficiency continues, calcium will get leached out of the bones to serve bodily functions. Over time, it can lead to soft, weak bones. In children, it causes the disease rickets and, in adults, osteoporosis.
Children diagnosed with rickets generally have a good prognosis so long as the disease is caught and treated early. Osteoporosis, however, is not curable. Instead, treatments are meant to slow the progression of the disease.
Who is At Risk of Calcium Deficiency?
According to the National Health and Nutrition Examination Survey, many people in the United States are not getting enough calcium in their diets to meet the recommended daily intakes. In particular:
- Boys and girls 9-13 years old
- Girls 14-18 years old
- Women 50-70 years old
- Men and women 70+ years old
Additionally, vegans are also at a high risk of calcium deficiency. In one study, it was found that vegans had a higher risk of bone fractures than meat eaters and vegetarians. Of course, this study does not mean that all vegans are deficient in calcium, but vegans (particularly those who fall into the above groups) should be cautious that they are getting enough calcium.
People who consume excess amounts of caffeine or alcohol (which adversely affects both calcium absorption and calcium release from the bones) may need to consume extra calcium. Also, people who consume very high amounts of protein may need to consume extra calcium because protein can deplete calcium from the bones.
It is very difficult to get the RDA of calcium on the vegan diet (it would take about 4 cups of darky leafy greens, 1 cup of fortified tofu, and a cup of fortified soy milk). Because of this, vegans should probably consider taking a calcium supplement with vitamin D. Vegetarians may also want to consider a calcium supplement because many vegetarian foods can inhibit calcium absorption.
There are two main types of calcium supplements:
- Calcium carbonate
- Calcium citrate
Calcium carbonate is more common because it is cheaper. However, it is not as easily absorbed as the more-costly calcium citrate supplements. Calcium carbonate should be taken with food whereas calcium citrate can be taken on an empty stomach.
Because the amount of calcium absorbed decreases with the size of dosage, people should space their calcium dosages throughout the day (such as in the morning and evening). For maximum efficiency, no more than 500mg of calcium should be taken at once.
You can find our recommendations for vegan calcium supplements here.
Can You Get Too Much Calcium?
When consumed through food, getting too much calcium does not seem to be a problem. However, there could be serious repercussions for taking too much calcium as a supplement. Studies have now shown that calcium supplements are linked to heart disease, including increased risk of heart attack. The theory as to why this is so is because there is too much calcium circulating through the blood at once. Without Vitamin K2 to carry the calcium where it needs to go (more on Vitamin K2 here), the calcium hardens in the arteries causing atherosclerosis. If you are going to take a calcium supplement, it seems advisable to take one which also contains Vitamin K2, or to eat natural sources of K2 such as fermented foods.
Taking excessive amounts of calcium through supplements can cause constipation, bloating and gas. There is also evidence that high dosages of calcium from supplements could cause kidney stones. There is some conflicting evidence that excessive calcium levels could lead to prostate cancer. Some evidence also shows that calcium could interfere with absorption of icon and zinc.
While problems from taking too much calcium are unlikely, people should try to stay within the upper intake level as recommended by the Institute of Medicine.
|Age/Group||Upper Level Intake (mg/day)|
Best Vegan Sources of Calcium
These vegan foods are high in calcium and also have a high bioavailability of calcium:
- Seaweeds (kelp, wakame, hijiki)
- Blackstrap molasses
- Fortified soy milk
- Fortified tofu
- Fortified orange juice
- Kale, Swiss chard
- Cabbage family (boy choy, Brussel spouts)
- Dandelion greens
See our recommendations for vegan calcium and bone supplements here.