Nutrition 101: Calcium

Calcium 101

(HealthCastle.com) Calcium is an essential mineral, required by our bodies at all ages, not just during growth years. The two most common supplement forms of calcium are calcium carbonate and calcium citrate.

Recommended Intakes

The Dietary Reference Intakes (DRI) for calcium are shown below:

Age Group

Recommended Dietary Allowance (RDA) per Day Tolerable Upper Intake Level (UL) per Day
Adults    
19 to 50 years 1,000 mg 2,500 mg
51 to 70  years

1,000 mg male
1,200 mg female

2,000 mg
71 years and up 1,200 mg 2,000 mg
Kids and Youth    
1 to 3 years 700 mg 2,500 mg
4 to 8 years 1,000 mg 2,500 mg
9 to 18 years 1,300 mg 3,000 mg
Special Considerations    

Pregnant or lactating women 14 to 18 years

1,300 mg

3,000 mg

Pregnant or lactating women 19 to 50 years 1,000 mg 2,500 mg

Note: For very young children, the reference levels provided are adequate intake (AI): 200 mg/day for infants up to 6 months old, and 260 mg for infants between 7 to 12 months old. There is no actual recommended dietary intake for these age groups.

Good Sources of Calcium

What Does Calcium Do?

Calcium is the most abundant mineral in the body. Ninety-nine percent of it is stored within our bones and teeth, with 1% circulating as serum calcium in the blood. The metabolism of calcium in the body is very tightly regulated, and the body uses the bones and teeth as both the source and the reserve of calcium to maintain serum calcium levels. Calcium is important in the maintenance of healthy bones and teeth, as many of us know, but it is also involved in ensuring proper muscle function, nerve transmission, cellular signaling, vascular contraction and dilation, and hormone secretion. Calcium is also needed for blood to clot.

Top Calcium-Rich Foods

Here are some of the richest calcium sources in the diet:

Food Calcium per serving
Plain yogurt, 6 oz ~ 300 mg
Fruit-flavored yogurt, 6 oz ~ 200 to 250 mg
Sardines, Atlantic, 3 oz 351 mg
Mozzarella cheese, 1.5 oz 333 mg
Sardines, 3 oz 325 mg
Cheddar cheese, 1.5 oz 307 mg
Milk, nonfat, 1 cup 299 mg
Milk, reduced fat, 1 cup 293 mg
Milk, whole, 1 cup 276 mg
Non-dairy milk alternatives (e.g., rice, soy, nut), calcium fortified, 1 cup 200 to 300 mg depending on manufacturer
Collard greens, chopped, cooked, 1 cup 268 mg
Sesame seeds, 3 tbs 264 mg
Tofu, firm, 1/2 cup (made with calcium sulfate)* 253 mg
Sardine, Pacific, canned with bones, 3 oz 214 mg
Spinach, frozen (chopped or leaf), 1 cup 201 mg
Salmon, sockeye, canned 3 oz 197 mg
Mustard greens, boiled, drained, 1 cup 165 mg

*Two common coagulating agents used to prepare tofu are magnesium chloride (nigari) and calcium sulfate. Tofu made with calcium sulfate will contain more calcium than nigari-style tofu. 

Calcium is better absorbed under acidic conditions. Stomach acid production increases in the presence of food. Therefore, if you choose to take calcium supplements, it is best to take the supplement with a meal. There is a difference: calcium citrate - such as in Citracal and Solgar - is the "acidic" form and can therefore be taken on an empty stomach, whereas calcium carbonate - such as in Tums and Caltrate - is the "alkaline" form, which should be taken with a meal. In either case, taking the supplement with food will ensure you are optimizing the absorption of calcium. The efficiency of absorption decreases as calcium intake increases, so it is best to break up the doses throughout the day (no more than 500 mg at once). 

Nutrition Facts Label and the % Daily Value

In the US: The daily value for calcium is 1,000 mg, which is the same level as the DRI for adults age 19-50. The % daily value gives you an idea of how much calcium is in the food you eat. The number you see on the Nutrition Facts label is a percentage calculated by dividing the amount of calcium in one serving of the food by the daily value. So, for example, a cup of calcium-fortified soy milk containing 200 mg calcium per serving would have 20% of the daily value (DV) for calcium. Foods containing 20% or more of the DV is considered to provide a high level of calcium.

In Canada: The daily value for calcium is 1,100 mg, which is slightly higher than the DRI level for adults. Using the same example, the cup of calcium-fortified soy milk containing 200 mg calcium would be labeled as containing 18% DV. Health Canada considers a food to deliver a high level of calcium if it contains 15% DV or higher per serving.

Nutrient Interactions

Magnesium: Both calcium and magnesium play important roles in bone formation and nerve and muscle functions. 

Phosphorus: Phosphorus is needed alongside calcium in the maintenance of healthy bones and teeth.

Vitamin D: Vitamin D is required for calcium to be absorbed and metabolized properly in the body. 

Vitamin K: Both calcium and Vitamin K are needed to help blood platelets form a clot at the site of a wound.

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