Calcium is essential for optimal bone health throughout your life. Although diet is the best way to get calcium, supplements may be required if your diet falls short. Before you consider calcium supplements, be sure you understand how much calcium you need, the pros and cons of calcium supplements, and which type of supplement to choose.
With respect to calcium supplements, the four most commonly available sources are listed below. As one can see, the percentage of each that can be assimilated by the digestive system and incorporated into the bone is highly variable. Moreover, while insufficient calcium intake is a serious problem, recent research indicates an overload of calcium caused by drinking too much milk, along with taking calcium supplements or antacids, can cause a host of serious side effects. These include: hypercalcemia, (a shift in the body's acid/base balance towards alkaline), calcinosis and nephrocalcinosis, (calcium deposits in the tissues and kidneys), kidney stones, plaque in the arteries, and an increased risk of heart attack, stroke, and kidney disease.
• Calcium carbonate 40 percent elemental calcium
• Calcium citrate 21 percent elemental calcium
• Calcium gluconate 9 percent elemental calcium
• Calcium lactate 13 percent elemental calcium
The recommended daily allowance (RDA) of calcium for an adult, published by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies, is 1000–1200 mg (1200 mg for age 70 and older) and based on the latest research, it is best to get as much calcium as possible from natural food sources while minimizing supplemental calcium - especially calcium carbonate. Interestingly, the number the RDA is based on, (the number that really matters), is how much calcium you absorb, not how much you eat. The average adult needs 300-400 mg of calcium that can be readily metabolized and used to satisfy the body’s calcium requirements.
The following is the very short list of high calcium food items that have been tested for bioavailability. Note: Minor sources have been omitted from this list, as well as fortified foods (such as calcium fortified orange juice, calcium set tofu, calcium fortified soy beverage, etc.), as they include nothing more than the basic food item with supplemental calcium added.
Food Serving Size Calcium absorbed per serving
Collard greens 1 cup cooked 173 mg
Canned salmon (6 oz with bones) 6-ounce serving 114 mg
Turnip greens 1 cup cooked 102 mg
Milk, Lactaid, yogurt 1 cup 96 mg
Cheese (hard such as cheddar) 1 ½ oz 97 mg
Sardines (with bones) 1 can (3.75oz) 95 mg
Bok choi 1 cup cooked 69 mg
Broccoli 1 cup cooked 57 mg
Kale 1 cup cooked 46 mg
Mineral water 20oz bottle 41 mg
Mustard greens 1 cup cooked 42 mg
Chinese spinach ½ cup 29 mg
Almonds 1/4 cup 22 mg
Beans (white) 4 oz 25 mg
Beans (pinto) 4 oz 15 mg
Beans (red) 4 oz 10 mg
Whole wheat bread 1 slice 17 mg
A glance at this list makes it immediately apparent that without milk and/or milk products it is very difficult to meet the daily requirement for bioavailable calcium without relying heavily on supplements. This, however, is complicated by the fact that approximately 25% of Americans are lactose intolerant. Fortunately, Lactaid can be substituted for milk, lactose free yogurt is readily available, and many lactose intolerant people can eat small portions of hard cheeses without a problem. The reason being that most of the lactose in cheese is converted to lactic acid when the milk and/or cream is cultured, and more drains off with the whey during the aging process.
Another little known fact is that green leafy vegetables, which are very rich in calcium, often contain phytates and/or oxylates. These “antinutrients” bind to the calcium in the cells of the plant and block bioavailability. A good example is spinach, which contains 115mg of calcium per ½ cup, but provides only 6mg that can be metabolized and used to meet the body’s calcium requirements. Furthermore, when these foods are included with a meal, the phytates and oxylates they contain bind with the calcium in other food items you eat and block its absorption as well.
Vegetables high in oxylates include: carrots, spinach, okra, kale, chard, beet greens, rhubarb, collard greens, broccoli rabe, turnip greens, and Brussels sprouts. From the above chart, however, it is obvious that collard greens and turnip greens are so high in calcium that the negative impact of the oxylates on other food items is more than offset by their high bioavailable calcium content.
Foods high in phytates include: whole grains, nuts, seeds, beans, and legumes; with beans being the biggest concern. Fortunately, the phytates in whole wheat bread are removed during leavening, so this staple remains both a healthy food and a good source of calcium.
Lastly, it has been shown that vitamin D3, magnesium, and vitamin K2 work either synergistically with calcium, or contribute to its absorption.
Based on the aforementioned research, eating a nutritious diet, plus the following suggested supplementation should help prevent osteoporosis and maintain strong healthy bones, nerves, and muscles.
cup of milk or yogurt, (either regular or lactose free) 96 mg
2 ounces of low fat hard cheese 129 mg
1 can of sardines, 1 serving salmon, or a third portion of dairy 95 mg
400mg of calcium citrate (21% elemental calcium) 84 mg
Total 404 mg
Significantly, once the daily calcium requirement has been met, (with the above suggestion, or any variation), antinutrient containing green vegetables, which taste good, contain beneficial fiber, vitamins, minerals, and disease fighting phytochemicals can be enjoyed with meals.
Lastly, it is recommended that from 1500 - 2000 mg vitamin D3, 200 mcg vitamin K2, and 500mg Magnesium be taken daily to augment the activity and/or absorption of calcium.