Wayne State researchers observed that most calcium supplements on the market are composed mainly of antacids--and the calcium benefit may be secondary to the antacid.
"If you think about it, your bone is like a stick of chalk. If you put it in acid, it's going to dissolve. If you neutralize the acid, the bone stays strong. We began to think about the link between dietary acid intake and osteoporosis, or thinning of the bones," said Dr. Warren Lockette, lead author on the study and professor of neurosurgery at the WSU School of Medicine.
While it's clear that calcium supplements make bones stronger, it isn't clear why. Furthermore, it isn't clear whether calcium is the primary preventive force against osteoporosis. Based on this study, WSU doctors now believe acid metabolism is just as important as calcium consumption in maintaining strong bones.
"We think there's no question that calcium supplementation is beneficial in making bone strong. We're just not so sure it's the calcium in the supplements that is really important. We think it may be the ability of those calcium supplements to buffer against acid that's found in the body--in other words, the antacid effect of most of the supplements," Dr. Lockette said.
The Wayne State University study, "Ethnic Differences in Titratable Acid Excretion and Bone Mineralization," initially sought to explain why black Americans have such a low incidence of osteoporosis, even though they generally consume and absorb less calcium than whites. On the other hand, older white women of European descent have the highest rate of osteoporosis, even though they are the largest consumers of dietary and supplemental calcium.
The study ultimately found that the ethnic differences in bone density had more to do with acid metabolism than calcium. If the body can't neutralize acid efficiently, calcium benefits may be lost.
To test his hypothesis-that the way an individual handles dietary acid affects bone health-Dr. Lockette and his colleagues tested a group of 33 United States Navy SEAL trainees. This cohort of highly trained athletes showed a strong relationship between the prevalence of stress fractures and acid excretion. Those trainees who had the highest acid output were most likely to have stress fractures during their physical training.
Co-author, Dr. Stephen Farrow, is a geriatrician who was intrigued by differences in the incidence of osteoporosis between his African-American and European-American patients. He collaborated on this study to try and understand the ethnic variables associated with bone density and bone mineralization.
"We found that generally, people of European-American descent had higher excretions of calcium and higher excretions of hydrogen ion-or acid-in their urine than did African Americans. We don't know whether this is the reason for the difference in frequency of osteoporosis between these two groups, but we feel it deserves further investigation," said Dr. Farrow, assistant professor of internal medicine.
Wayne State researchers believe that calcium could be a surrogate marker for something else in the diet. That is, diets high in calcium may also be high in acid. This link changes the way we view bone health and could help doctors design new prevention plans for people who are at risk for bone deterioration, fractures, or osteoporosis.
"This is a whole new area of investigation that has implications for the aging population in the United States. It explains or may help explain the differences among ethnic groups in bone mineralization. It may have some predictive value at who gets osteoporosis. Also, if endogenous acid production or dietary acid intake really does contribute to how well one's bones mineralize, then we really need to look at our nutritional guidelines, not just in terms of calories, fat content, or sodium intake, but also in terms of acid intake," Dr. Lockette said.
Dr. Lockette's current studies are trying to determine whether age-related declines in acid excretion contribute to the progression of osteoporosis in a more sedentary population.
Full text of the journal article is available at: http://www.acsm-msse.org/.
(February, 2002, page 295)
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With more than 1,000 medical students, Wayne State University is the nation's largest single-campus medical school. Together with the Wayne State University Physician Group, the school is a leader in patient care and medical research in a number of areas including cancer, genetics, women and children's health and the neurosciences.