Calcium plays important role in bone health
Calcium is in the news more than most other nutrients due to its important role in bone health. Because national dietary surveys indicate that many people consume too little calcium, many foods are being fortified with calcium to help people boost their intake.
Question: How much calcium do we need each day?
Answer: Currently, the Institute of Medicine recommends 1,000 milligrams (mg) of dietary calcium per day for adults from age 19 to 50. Recommended daily calcium intake for those age 9 to 18 is 1,300 mg per day, and for those over 50, 1,200 mg per day. To put this into perspective, a cup of milk (8 ounces) has about 300 mg of calcium.
Q: Why does the body need so much calcium?
A: Besides its role in bones, calcium also exists dissolved in body fluids. The body tightly regulates the concentration of calcium in the blood and cells. This tightly controlled calcium concentration is required for basic body functions like muscle contraction and nerve function.
Bones continuously release and take up calcium to maintain calcium levels in body fluids. Some of this dissolved calcium is lost from the body each day, and failure to replace lost calcium with calcium from foods results in bone loss.
Q: What foods provide enough calcium to meet recommended intakes?
A: Recommendations for calcium intake are based on the assumption that the body can extract and absorb about 30 percent of the calcium in the diet. Milk products and calcium-fortified juices are reliable rich sources of well-absorbed calcium.
Some types of tofu provide a significant amount of easily absorbed calcium, and some types do not. If the food label indicates "30 percent," then a serving provides 300 mg. Sardines and other canned fish that include bones also can provide well-absorbed calcium.
Certain green vegetables like choy sum, kai choy and turnip greens are good calcium sources. Spinach is high in calcium, but only about 5 percent can be absorbed.
Broccoli, kale and cabbage contain modest amounts of well-absorbed calcium, but they must be consumed in fairly large amounts to provide a significant amount of calcium.
Q: Can consuming too much calcium cause problems?
A: Yes, the Institute of Medicine set the upper limit for calcium at 2,500 mg per day. In some people, excessive calcium intake has caused kidney problems. In contrast, a low calcium intake can increase the risk of kidney stones.
Also, calcium interferes with the absorption of minerals such as iron and zinc. Consuming high-calcium foods or supplements with every meal can lead to iron deficiency.
Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S. are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dr. Dobbs also works with University Health Services.