PITTSBURGH, April 1, 2003 -A rigorous clinical study that compared the performance of two well-known calcium supplements, calcium carbonate (Os-Cal) and calcium citrate (Citracal), has revealed no differences at all in their ability to be absorbed and used in the body by postmenopausal women, according to data published in the April issue of the Journal of the American College of Nutrition1.
The study looked at the absorption levels of Os-Cal and Citracal in postmenopausal women in the spring of two successive years, the first year with pretreatments of vitamin D supplements and the second year without. Both of these calcium supplements were absorbed better with higher levels of vitamin D, but with or without vitamin D pretreatment, Os-Cal and Citracal were absorbed equally
No More Form Over Function
"The levels of calcium absorption were indistinguishable between calcium carbonate and calcium citrate, as we have previously shown in clinical studies," reported Robert P. Heaney, M.D., Professor of Medicine, Osteoporosis Research Center, Creighton University, Omaha, NE, and lead investigator of the study. "The two calcium supplements were equally bioavailable."
What the study did show, however, was the important role vitamin D plays in increasing the absorption of calcium (both carbonate and citrate). With vitamin D pretreatment, the mean calcium absorption was 65% better (35.3% with it and 22.5% without it).
The study concluded that among the "free-living" postmenopausal women tested, calcium absorption begins to drop off if the vitamin D status falls below a level of about 80 nmol/L of 25(OH)D-the main vitamin D metabolite that circulates in serum.
"Previously, we thought a blood vitamin D level of 40 or 50 nmol/L might be the lower end of sufficient to absorb calcium well," Dr. Heaney said. "Now we know that's much too low for a woman to get the full benefit of calcium intake. The blood level should be no lower than about 80 nmol/L of vitamin D."
"The results dovetail nicely with those of another study published recently2 showing that higher vitamin D intake reduced the number of total fractures by 22% in both women and men who were 65 to 85 years old and the number of fractures in major osteoporotic sites by 33%," Dr.
Heaney added. "The blood vitamin D levels in the men and women in this study were almost exactly the same as those in our study on the effects of absorption."
In the bioavailability study, a total of 34 healthy, free-living postmenopausal women (approx 60 years of age) were studied. The women all received a single dose of an oral calcium supplement as part of a standard low-calcium breakfast. They ate a low-calcium lunch. Their blood was tested several times throughout the day. Calcium absorption was measured by standard methods. Each woman was randomized to receive 500 mg of Os-Cal or 515 mg of Citracal. About a week later each woman was tested again, this time after breakfast with the supplement she hadn't received previously.
In the first phase, the supplemental vitamin D was given on alternate days for three weeks leading up to the test breakfast. It produced a serum level of 86.5 ± 24 nmol/L of 25(OH)D. That compared with a serum level of 50.1 ± 26 nmol/L of 25(OH)D without supplemental vitamin D in the second phase a year later.
The study was supported by Creighton University and a research grant awarded by GlaxoSmithKline Consumer Healthcare.
About Calcium Intake
The U.S. Department of Health and Human Services reports that only one in 20 adult Americans meets currently recommended guidelines for optimal calcium intake, and a National Institutes of Health select panel recommended a unified public health strategy to ensure optimal calcium intake in the American population. Os-Cal contains calcium carbonate, which has a higher percentage of elemental calcium - the calcium the body actually uses - than calcium citrate. Taken in a simple dosing regimen with meals, Os-Cal can help consumers easily meet their daily calcium requirement, which is up to 1,500 mg for adults older than 50.
About Vitamin D
Vitamin D aids in the absorption of calcium. The primary source of vitamin D is exposure to sunlight, which stimulates the production of vitamin D in the skin. Capacity to produce vitamin D in the skin declines with age. Milk is fortified with vitamin D in the U.S. Few other foods are good sources of vitamin D: fatty fish (salmon, herring, swordfish) and egg yolk. Supplements such as Os-Cal play an important role in helping people consume the recommended amount of vitamin D daily. Two Os-Cal 500 Plus D tablets provide 1,000 mg of calcium and 400 IU of vitamin D.
Americans can help prevent and slow the progression of osteoporosis by following a healthy lifestyle, getting adequate calcium and vitamin D (through dietary sources and calcium with vitamin D supplements, such as Os-Cal), and engaging in weight-bearing exercise such as walking, dancing or tennis. The National Osteoporosis Foundation recommends a bone-mineral density test for postmenopausal women younger than 65 with one or more risk factors, and for all women 65 or older irrespective of risk factors.
Osteoporosis, or porous bone, is a disease that is a major public health threat for more than 28 million Americans. According to the National Osteoporosis Foundation, eight million American women and two million men have osteoporosis, and millions more have low bone density. Each year, osteoporosis leads to 1.5 million fractures, often of the hip, spine and wrist. An average of 24% of hip fracture patients, age 50 and over, die in a year following their fractures. Estimates of direct national health care costs to treat hip and other bone fractures associated with osteoporosis exceed $15 billion annually. These costs are expected to grow by more than $60 billion by the year 2020 unless more aggressive steps are taken to prevent and treat the disease.
Manufactured by GlaxoSmithKline Consumer Healthcare, Os-Cal is the brand preferred by doctors for women at risk of osteoporosis and has been clinically proven effective to help maintain bone mass in more studies than any other brand. Every batch of Os-Cal is quality-tested to meet USP dissolution standards. Os-Cal's concentrated calcium carbonate formula provides 60% more elemental calcium per pill than supplements containing calcium citrate, and is less expensive per dose.
Consumers can call toll-free 1-866-538-3687 to get an osteoporosis risk assessment chart and to learn more about calcium supplementation. Information is also available at the Os-Cal Web site at www.os-cal.com and the Calcium Information Web site at www.calciuminfo.com.
About GlaxoSmithKline Consumer Healthcare
GlaxoSmithKline Consumer Healthcare is one of the world's largest over-the-counter healthcare companies and it also ranks second globally in sales of oral care products. Its more than 45 well-known products include such medicine cabinet staples as Abreva®, Aquafresh® toothpastes and toothbrushes, Nicorette®, NicoDerm® CQ, Oxy®, Sensodyne® and Tums®.
GlaxoSmithKline-one of the world's leading research-based pharmaceutical and healthcare companies-is committed to improving the quality of human life by enabling people to do more, feel better and live longer.
Os-Cal® is a registered trademark of GlaxoSmithKline
Citracal® is a registered trademark of Mission Pharmacal
Editor's Note: To obtain copies of the study and interviews with Robert P. Heaney, M.D., F.A.C.P., F.A.S.N.S., F.A.C.N., Professor of Medicine, Osteoporosis Research Center at Creighton University in Omaha and co-researcher Adrianne Bendich, Ph.D., F.A.C.N., Clinical Director, Calcium Research at GlaxoSmithKline Consumer Healthcare, contact Linda Stanier at
1. Robert P Heaney, M Susan Dowell, Cecilia A Hale, Adrianne Bendich. Calcium absorption varies within the reference range for serum 25-hydroxyvitamin D. J Am Coll Nutr 22(2):142-146, 2003.
2. Daksha P Trivedi, Richard Doll, and Kay Tee Khaw. Effect of four monthly oral vitamin D3 (cholecalciferol) supplementation on fractures and mortality in men and women living in the community: randomized double blind controlled trial. BMJ 2003; 326: 469.