Osteoporosis

Diet and Osteoporosis

An adequate intake of calcium is an important nutrient in the prevention of osteoporosis. Dietary calcium exerts its greatest effect on bone mineral density from preadolescence to young adulthood. Until peak bone mass is attained at approximately 30 years of age, bone formation exceeds the rate of bone resorption. The amount of bone mass an individual has by age 30 will strongly influence susceptibility to fractures in later years. The Recommended Dietary Allowance (RDA) for calcium for adolescents and young adults up to age 24 is 1,200 mg a day. For adult men and women, the RDA for calcium is 800 mg per day.

Because of their lower bone mineral density and total bone mass, women are more susceptible to osteoporosis. Also, after menopause women produce less estrogen, which further accelerates bone loss. Therefore, adequate calcium intake is also important for elderly women. Although the rapid bone loss that occurs for about five years after menopause cannot be prevented by calcium supplementation, total calcium intake in the range of 1,500 mg a day can reduce bone loss in later years.

National surveys of the general population such as the third National Health and Nutrition Examination Survey reveal that children, most women, and elderly men do not obtain the RDA for calcium. Half of all adult women consume less than 500 mg of calcium a day. Female adolescents who have a poor calcium intake are a particular concern because they may be setting themselves up for an increased risk of subsequent osteoporosis. Therefore, they should be encouraged to adopt dietary habits that will promote an increased intake of calcium during this critical period.

The prevalence of calcium deficiency among women becomes even more serious in light of claims by the National Institutes of Health (NIH) and nutrition experts that the calcium needs of adult women actually are well above the recommended 800 mg level. The NIH recommends that premenopausal adult women consume 1,000 mg per day. Women of any age who are on estrogen replacement therapy should also consume 1,000 mg per day since they can still lose bone mass. Postmenopausal and amenorrheic women who are not on estrogen should consume 1,500 mg per day.

Dairy products represent the best sources of calcium. An eight-ounce glass of milk or 1/3 cup of non-fat powdered milk each contains about 300 milligrams of calcium. Skim or low-fat versions of milk, yogurt, cottage cheese, or cheese often provide the same amount of calcium as the regular versions of these foods, but contain less fat and calories.

Other good sources of calcium are sardines (because of the bones) and oysters. Broccoli and greens (kale, collard, turnip, and mustard) are good non-fat vegetable sources of calcium. Tofu which has been processed with calcium sulfate can also be a good source of calcium.

Food is the ideal way to obtain calcium. However, the American diet, if devoid of dairy products, contains only about 300 mg of calcium per day. Because only a few calcium fortified foods are currently available, many people opt for calcium supplements. A registered dietitian can provide advice on how to obtain the appropriate amount of calcium from food, and when necessary, from supplements.

Calcium carbonate (Tums or a generic equivalent) is an inexpensive and acceptable calcium source. Calcium carbonate is 40% calcium, so a 500 mg tablet actually provides 200 mg of elemental calcium. Such antacids that contain calcium are practically the same as dietary supplements. The primary difference between the two is in the marketing -- when calcium carbonate is marketed as a calcium supplement, it costs more.

Bioavailabilty is an important concern when selecting a supplement. Some brands of supplements do not dissolve as they should in the stomach. A simple test can be performed if the ability to absorb the supplement is questioned. Place the supplement into 1/2 cup of vinegar and let stand for 30 minutes. If the tablet is not completely dissolved at this time, try another brand.

Calcium supplements can cause constipation and abdominal distention. Problems can be minimized by spreading the supplement throughout the day and taking it with meals. Combining the supplement with meals also promotes greater calcium absorption due to greater gastric acidity and slower transit time in the gut. Divided doses are also recommended for people with achlorhydria, a common finding in the elderly.

Bone meal and dolomite should not be used as calcium supplements because they may contain harmful amounts of lead, arsenic, mercury, and other potentially toxic minerals.

Too much calcium can be harmful. In susceptible people, excessive calcium intake increases the risk of kidney stones. Excessive calcium from diet or supplements may also interfere with the absorption of iron. The National Research Council recommends that calcium supplements not exceed the RDA.

Many other nutrients influence bone formation, thus underscoring the importance of a balanced diet. High intakes of protein and sodium increase the amount of calcium lost in urine. High protein intakes, particularly of sulfur-containing amino acids, increase urinary calcium excretion. Diets high in sodium likely contribute to calcium losses because as sodium is excreted in the urine, it pulls calcium with it. People consuming a typical Western diet high in protein and sodium excrete more calcium than do those consuming lower levels of protein and sodium. Vegans can maintain calcium balance on a lower intake because their diets often contain less protein and sodium.

Vitamin D is important for bone health because its active form stimulates intestinal calcium absorption. Older individuals are especially at risk for vitamin D deficiency due to a lack of sunlight, poor diet, and decreased synthesis and absorption. Individuals at high risk for osteoporosis may benefit from taking moderate amounts of supplemental vitamin D, usually in the amount of 20 micrograms a day or 800 IU. The adult RDA for vitamin D is 5 micrograms or 200 I.U.

Alcohol abuse is associated with detrimental effects on bone mass. Alcohol is thought to depress bone formation by directly reducing osteoblastic activity. Also, dietary intakes of heavy drinkers are often lacking in essential nutrients (minerals, protein, and vitamin D). These low levels (in particular of vitamin D) can cause diminished intestinal absorption of calcium, which can lead to mobilization of calcium from bone. Lastly, alcohol abuse creates social situations that favor accidents and falls. Moderation in alcohol consumption is recommended to promote optimal bone health.

Caffeine ingestion increases urinary calcium excretion. When coupled with poor calcium intake, a heavy consumption of caffeine could compromise bone integrity. Therefore, moderation in intake of caffeinated beverages such as coffee, tea, and some soft drinks, is recommended.