Calcium absorption and bone density

Vicki Koenig, MS, RD, CDN

Calcium is important for bone health, yet most of us don't get enough. Studies show that 19 out of 20 women and 9 out of 10 teenage girls don't meet their daily requirement. From toddlers on, children don't get enough calcium, according to the Centers for Disease Control.

The issue of calcium absorption

Calcium is not a well-absorbed mineral. The dietary reference standards take this into account. Adults need 1000 mg per day. We need this much to absorb enough for our needs. We only absorb 23–37%.

In a review of about 14 studies, calcium had the following average absorption rates:

Rates of absorption vary depending on age, overall diet, estrogen status and many other considerations.

Positive influences on calcium absorption

The rate of calcium absorption can be improved.

• Vitamin D helps increase calcium absorption in the intestine and promote bone density. The recommended daily intake of vitamin D for adults is 400 IU. Stonyfield Farm yogurts have 20% of the daily value for vitamin D.
• Stomach acid helps calcium dissolve, which increases absorption. Individuals with inadequate stomach acid have lower calcium absorption.
• Exercise helps increase calcium absorption.

Negative influences on calcium absorption

• Oxalates found in spinach, chocolate, rhubarb, walnuts and tea bind calcium into insoluble complexes, reducing its absorption.
• Phytates found in bran, cereals, seeds and beans also bind calcium. Soy contains both phytates and soy isoflavones. Isoflavones help increase calcium absorption, balancing the phytates.
• Too much calcium at once. Only 500–600 mg is absorbed at one time.

Why bone health is important

Bone is a living, dynamic tissue constantly undergoing breakdown and formation as part of our body's natural cycle of growth and repair. Development of optimal bone mass during childhood and adolescence is critically important in preventing osteoporosis, especially considering the natural loss of bone mass later in life.

Stonyfield yogurt is an excellent way to meet your body's need for calcium. Its well-absorbed form of calcium is something most of us need more of.

For more information:

• Guéguen L and Pointillart A. "The bioavailability of dietary calcium." J Am Coll Nutr Apr 2000;19(2 Suppl):119S–136S.
• Heaney RP et al. "Bioavailability of the calcium in fortified soy imitation milk, with some observations on method." Am J Clin Nutr May 2000, 71(5):1166–1169.
• Miller GD et al. "Table 2. Comparison of Sources of Absorbable Calcium with Milk." From "The Importance of Meeting Calcium Needs with Foods." J Am Coll Nutr, Apr 2001; 20(2):168S–185.
• Weaver CM. "Should dairy be recommended as part of a healthy vegetarian diet?" Am J Clin Nutr, May 2009; 89(5):1634S–1637S.
• Weaver CM et al. "Choices for achieving adequate dietary calcium with a vegetarian diet." Am J Clin Nutr Sept 1999, 70(3):543S–548S.
• Zittermann A et al. "Evidence for an acute rise of intestinal calcium absorption in response to aerobic exercise." Eur J Nutr, 41(5):189–196:2002.