Nutrition and bone health

by Keith Nunes
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Bone health is a key concern of the baby boomer generation, and research is uncovering more about the relationship between nutrition and the structural support of the human body.

For example, a study published in the journal Archives of Osteoporosis indicates that not all dairy products are equally beneficial in promoting bone strength. The relationship between dairy products and bone health has been known for many years, but a study conducted at the Institute for Aging Research (I.F.A.R.) at Hebrew SeniorLife, an affiliate of Harvard Medical School, Boston, has found fluid milk and yogurt intake are associated with higher bone mineral density (B.M.D.) in the hip, but not the spine. Cream, on the other hand, may be associated with lower B.M.D. overall.

“Dairy foods provide several important nutrients that are beneficial for bone health,” said Shivani Sahni, Ph.D., lead author and a member of the musculoskeletal research team, at I.F.A.R. “However, cream and its products such as ice cream have lower levels of these nutrients and have higher levels of fat and sugar.”

The study indicated that two-and-a-half to three servings of milk and yogurt per day was associated with better bone density.

“More research is needed to examine the role of cheese intake, some of which can be high in fat and sodium, and whether individual dairy foods have a significant impact in reducing fractures,” Dr. Sahni said.

The I.F.A.R. researchers based the findings on data collected from a food frequency questionnaire completed by 3,212 participants from the Framingham Offspring study. They compared participants’ dairy intake with B.M.D. measurement, which revealed the benefits of milk and yogurt versus cream in largely middle-age men and women.

The research highlighted the fact that nutrient composition varies among dairy foods, and that choosing low-fat milk or yogurt over cream may increase the intake of protein, calcium and vitamin D while limiting the intake of saturated fats.

Dr. Sahni said the study is an example of a growing area of research focused on the relationship between nutrition and bone health. Past studies have suggested dairy products contain more than one beneficial nutrient, and for that reason certain dairy products may contribute more than others toward maintaining healthier bones.

Leafy green vegetables and bone health

A study from engineering researchers at Rensselaer Polytechnic Institute, Troy, Mich., shows how the protein osteocalcin plays a significant role in the strength of bones. The findings of the study may lead to new strategies and therapeutics for preventing osteoporosis and lowering the risk of bone fracture, according to the researchers.

The study shows how fractures in healthy bones begin with the creation of tiny holes, each measuring only about 500 atoms in diameter within the bone’s mineral structure. When a person falls, the force of the impact on the bone physically deforms a pair of joined proteins — osteopontin and osteocalcin — and results in the formation of nanoscale holes. The holes, which are called dilatational bands, act as a natural defense mechanism, and help to prevent further damage to the surrounding bone. However, if the force of the impact is too great or if the bone is lacking osteopontin, osteocalcin, or both, the bone will crack and fracture.

The multi-university study funded by the National Institutes of Health and led by Deepak Vashishth, head of the Department of Biomedical Engineering at Rensselaer, is the first to detail a bone fracture at the level of bone’s nanostructure. Partnering with Rensselaer on the study were Villanova University, the Hospital for Special Surgery in New York, and Yale University.

“This study is important because it implicates, for the first time, the role of osteocalcin in giving bone the ability to resist fracture,” Dr. Vashishth said. “Since osteocalcin is always the point of fracture, we believe that strengthening it could lead to a strengthening of the overall bone.”

With the knowledge of the role osteocalcin plays in a bone fracture, new strategies for strengthening the bond between osteocalin and osteopontin may be investigated, said Dr. Vashishth. Supplementing the body’s natural supply of osteocalcin, for example, may be one strategy for preventing or treating osteoporosis and other conditions leading to increased fracture risk, he said.

Osteocalcin must be in its carboxylated form to get absorbed into bone, and the protein is carboxylated by vitamin K, Dr. Vashishth said. He said future studies may investigate the relation between vitamin K intake, osteocalcin, and bone strength.

“Currently, all of the advice for treating osteoporosis is related to calcium,” he said. “We believe there’s more to the story than just calcium, and the results of this new study raise an important question about vitamin K.

“Leafy green vegetables are the best source of vitamin K — wouldn’t it be great if eating spinach and broccoli was not only healthy, but also good for your bones? We plan to investigate this link in the future.”

Results of the study, titled “Dilatational band formation in bone,” were published on-line in the Proceedings of the National Academy of Sciences. The study may be viewed by visiting www.pnas.org.

Calcium supplements, men and C.V.D. risk

A high intake of supplemental calcium appears to be associated with an increased risk of cardiovascular disease (C.V.D.) death in men but not in women in a study of more 388,000 participants between the ages of 50 and 71 years, according to a report published on-line first by JAMA Internal Medicine, a JAMA Network publication.

Calcium supplementation has become widely used, especially among the elderly population, because of its proposed bone health benefits. However, beyond calcium’s established role in the prevention and treatment of osteoporosis, its health effect on non-skeletal outcomes, including cardiovascular health, remains largely unknown and has become “increasingly contentious,” according to the authors of the study.

Qian Xiao, Ph.D., of the National Cancer Institute, Bethesda, Md., and colleagues examined whether the intake of dietary and supplemental calcium was associated with mortality from total C.V.D., heart disease and cerebrovascular diseases. The study participants were from the National Institutes of Health-AARP Diet and Health Study in six states and two metropolitan areas from 1995 through 1996.

During an average 12 years of follow-up, 7,904 C.V.D. deaths in men and 3,874 C.V.D. deaths in women were identified and supplements containing calcium were used by 51% of the men and 70% of the women. Compared with non-supplement users, men with an intake of supplemental calcium of more than 1,000 mg per day had an increased risk of total C.V.D. death, more specifically with heart disease. For women, supplemental calcium intake was not associated with C.V.D. death, heart disease death or cerebrovascular disease death.

Dietary calcium intake was not associated with C.V.D. death in men or women.

“Whether there is a sex difference in the cardiovascular effect of calcium supplement warrants further investigation,” the authors wrote in the study. “Given the extensive use of calcium supplement in the population, it is of great importance to assess the effect of supplemental calcium use beyond bone health.”

In a related commentary published with the National Cancer Institute study, Susanna C. Larsson, Ph.D., of the Karolinska Institutet, Stockholm, Sweden, wrote, “More large studies are needed to further assess the potential health risks or benefits of calcium supplement use on C.V.D. morbidity and mortality.

“Meanwhile, a safe alternative to calcium supplements is to consume calcium-rich foods, such as low-fat dairy foods, beans and green leafy vegetables, which contain not only calcium but also a cocktail of essential minerals and vitamins.”

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