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Nutrition and Metabolism


What is calcium?

Calcium is the most abundant mineral in human body. It is needed to support the structure and hardness of bones and teeth. It is also important for the proper function of the heart, muscles, and nerves. Human body cannot make calcium. So we have to get it from foods constantly.  Calcium deficiency often leads to osteoporosis in adults and rickets in children.

How is calcium used in human body?

About 99% of the calcium in human body is used to strengthen bones. Bones are formed by special cells in the body. These cells make a scaffold with proteins and then calcium and phosphorus form a crystal on top of this scaffold, making it stronger. The reminder (1%) of calcium found in circulating blood functions as cofactors for many important enzymes that are required for muscle function, nerve transmission and hormonal secretion.

What is the normal calcium level in human body?

Normal serum calcium levels of adult are between 8.5 and 10.5 mg/dL. Since serum levels are tightly regulated in a relatively narrow range, it provides little value about your calcium nutrition status. You need to seek help from your health providers to evaluate the calcium status of your body.

How much calcium do I need in my diet?

The RDA (Recommended Dietary Allowance) and UL (Tolerable Upper Intake Levels) for calcium by the Institute of Medicine of the National Academies are age and gender dependent (Table 1).  For an adult between 19-50 years old, the RDA is equivalent to the calcium in 3 cups of milk. Too little calcium intake risks deficiency while too much can result in soft tissue calcification, constipation and kidney stones.

Table 1. RDA and UL for dietary calcium by the Institute of Medicine of the National Academies.

Age RDA (mg/day) UL (mg/day)
1–3 years 500 2,500
4–8 years 800 2,500
9–13 years 1,300 3,000
14–18 years 1,300 3,000
19-50 years 1,000 2,500
51-70 years (men) 1,000 2,000
51-70 years (women) 1,200 2,000
71 and older 1,200 2,500

Should I take calcium supplement?

You should consider calcium supplement if you cannot get enough from foods. About 43% of people in the United States use calcium supplements. For several high risk populations, calcium supplements are the only solutions to meet the recommended calcium intake levels. These high risk populations include people following a vegan diet; people with lactose intolerance thus may limit dairy products; and people consuming large amounts of protein or sodium that causes excess calcium excretion. If you have certain medical conditions such as osteoporosis, inflammatory bowel disease, or celiac disease, your health providers will most likely recommend calcium supplements. You should always ask your doctor before taking any supplement.

Why dietary calcium is more important for people carrying certain gene variants?

Calcium homeostasis and bone metabolism require the VDR gene to function properly. One genetic variant of the VDR gene, carried by about 26% of human population, make people more susceptible to osteoporosis when calcium intake is low. Another genetic variant that controls the turn on or turn off of the VDR gene, carried by 21% of the human population, make their carriers grow short when calcium intake is insufficient.  For people who carry these genetic variants, sufficient calcium intake is critical. In addition, a variant of the LPH gene, carried by about 23% of human population, causes lactose intolerance. People carrying this genetic variant tends to get less calcium form dairy products and are at risk of calcium insufficiency. For these people, alternative dietary calcium sources or calcium supplements are especially important.

Which foods contain high level of calcium?

Cheese, yogurt, and milk are natural calcium-rich sources and the major food contributors of calcium in the United States. Nondairy calcium-rich sources include sardine fish, tofu, and several vegetables (Table 2). Foods fortified with calcium include many fruit juices, soy milk, cereals, cereal bars, protein bars, waffles, instant oatmeal and bread. You need to check the Nutrition Facts on the labels to know the amount of calcium you will be getting per serving.

Table 2. Common calcium-rich natural foods (fortified foods are not included).

Dairy products
Cheese, gruyere
Per 100 g (mg) 1011-1253
Per Serving (mg) 287-351
Serving Size 1 oz (28 g)
Cheese, parmesan
Per 100 g (mg) 1011-1253
Per Serving (mg) 287-351
Serving Size 1 oz (28 g)
Cheese, Romano
Per 100 g (mg) 1011-1253
Per Serving (mg) 287-351
Serving Size 1 oz (28 g)
Cheese, cheddar
Per 100 g (mg) 505-791
Per Serving (mg) 143-224
Serving Size 1 oz (28 g)
Cheese, provolone
Per 100 g (mg) 505-791
Per Serving (mg) 143-224
Serving Size 1 oz (28 g)
Cheese, Swiss
Per 100 g (mg) 505-791
Per Serving (mg) 143-224
Serving Size 1 oz (28 g)
Yogurt, plain, low fat
Per 100 g (mg) 183
Per Serving (mg) 448
Serving Size 1 cup (8 oz)
Milk, lowfat (1% milk fat)
Per 100 g (mg) 128
Per Serving (mg) 314
Serving Size 1 cup (8 oz)
Sardine fish (canned in oil, drained solids with bone)
Per 100 g (mg) 382
Per Serving (mg) 325
Serving Size 3 oz (85 g)
Nuts and Seeds
Almonds nuts, dry roasted
Per 100 g (mg) 267
Per Serving (mg) 76
Serving Size 1 oz (28 g)
Tofu, firm
Per 100 g (mg) 201
Per Serving (mg) 253
Serving Size 1/2 cup (126 g)
Bread, white
Per 100 g (mg) 138
Per Serving (mg) 40
Serving Size 1 slice (29 g)
Turnip greens and turnips
Per 100 g (mg) 128
Per Serving (mg) 209
Serving Size 1 cup (163 g)
Cabbage, chinese (pak-choi)
Per 100 g (mg) 93
Per Serving (mg) 158
Serving Size 1 cup (170 g)
Per 100 g (mg) 72
Per Serving (mg) 94
Serving Size 1 cup (163 g)
Per 100 g (mg) 47
Per Serving (mg) 43
Serving Size 1 cup (91 g)


How to get sufficient dietary calcium intake?

First you are recommended to use the GB Food Calorie and Nutrition Calculator to get the most accurate estimate of your current calcium intake.

To increase calcium intake, the best way is to eat calcium-rich foods as those shown in Table 2. Many fortified foods listed the calcium content in the Nutrition Facts.  Choose the ones with high calcium content while shopping.

For people who cannot get enough calcium from diet, calcium supplements are alternatives. However, you need to limit the supplement below the Tolerable Upper Intake Levels. You also need to take no more than 600 milligrams at a time to ensure proper absorption.

To make sure proper calcium absorption and function, you also need to get enough vitamin D and/or sufficient sunshine.

Coffee, alcohol, sodium, and red meat will either interfere with calcium absorption or lead to calcium depletion.  Avoid excessive consumption of these foods also helps meet your calcium needs.

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