September - October 2006

The Latest Information Coming from the Friedman School of Nutrition Science and Policy at Tufts University

Consuming Cola May Up Osteoporosis Risk for Older Women: Epidemiological Study Finds that Cola is Associated with Bone Mineral Density Loss

Boston — According to the National Osteoporosis Foundation, approximately 55 percent of Americans, mostly women, are at risk of developing osteoporosis, a disease of porous and brittle bones that causes higher susceptibility to bone fractures. Now, Katherine Tucker, PhD, director of the Epidemiology and Dietary Assessment Program at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, and colleagues have reported findings in the American Journal of Clinical Nutrition that cola, a popular beverage for many Americans, may contribute to lower bone mineral density in older women, a condition which increases risk for osteoporosis.

Tucker, also a professor at the Friedman School of Nutrition Science and Policy at Tufts, and colleagues analyzed dietary questionnaires and bone mineral density measurements at the spine and three different hip sites of more than 2,500 people in the Framingham Osteoporosis Study whose average age was just below 60. In women, cola consumption was associated with lower bone mineral density at all three hip sites, regardless of factors such as age, menopausal status, total calcium and vitamin D intake, or use of cigarettes or alcohol.

However, cola consumption was not associated with lower bone mineral density for men at the hip sites, or the spine for either men or women. The results were similar for diet cola and, although weaker, for decaffeinated cola as well.

Men reported drinking an average of six carbonated drinks a week, with five being cola, and women reported consuming an average of five carbonated drinks a week, four of which were cola. Serving size was defined as one bottle, can or glass of cola. "The more cola that women drank, the lower their bone mineral density was," says Tucker, who is corresponding author of the study. "However, we did not see an association with bone mineral density loss for women who drank carbonated beverages that were not cola."

"Carbonated soft-drink consumption increased more than three-fold" between 1960 and 1990, cite the authors. They also note that more than 70 percent of the carbonated beverages consumed by people in the study were colas, all of which contain phosphoric acid, an ingredient that is not likely to be found in non-cola carbonated beverages.

While previous studies have suggested that cola contributes to bone mineral density loss because it replaces milk in the diet, Tucker determined that women in the study who consumed higher amounts of cola did not have a lower intake of milk than women who consumed fewer colas. However, the authors did conclude that calcium intake from all sources, including non-dairy sources such as dark leafy greens or beans, was lower for women who drank the most cola. On average, women consumed 1,000 milligrams of calcium per day, and men consumed 800 milligrams per day, both lower than the daily recommended 1,200 daily milligrams for adults over age 50.

"Physiologically, a diet low in calcium and high in phosphorus may promote bone loss, tipping the balance of bone remodeling toward calcium loss from the bone. Although some studies have countered that the amount of phosphoric acid in cola is negligible compared to other dietary sources such as chicken or cheese," Tucker says, "further controlled studies should be conducted to determine whether habitual cola drinkers may be adversely affecting their bone health by regularly consuming doses of phosphoric acid that do not contain calcium or another neutralizing ingredient."

Tucker stresses that as with any epidemiological study, the results should be taken with caution. "We are not certain why women who drank more cola also had lower bone mineral density," says Tucker. Although adjustment for fruit juice intake did not change results, women in the study who drank a considerable amount of cola not only consumed less calcium, but less fruit juice as well. Previous studies have also shown that low fruit and vegetable intake may affect bone mineral density.

The message from experts is clear that overall nutritional choices can affect bone health, but "there is no concrete evidence that an occasional cola will harm the bones," says Tucker. "However, women concerned about osteoporosis may want to steer away from frequent consumption of cola until further studies are conducted."

Tucker, KL, Morita, K, Qiao N, Hannan MT, Cupples A, Kiel DP. American Journal of Clinical Nutrition. (October) 2006; 84(4). "Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study."

Prescribe Exercise for Older Adults for Better Health

For many older adults, a visit to the doctor is not complete without the bestowal of at least one prescription. What if, in addition to prescribing medications as necessary, physicians also prescribed exercise? Ann Yelmokas McDermott, PhD, a researcher in the Lipid Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging (USDA HNRCA) at Tufts University, and Heather Mernitz, PhD, now of the Nutrition and Cancer Biology Laboratory at the USDA HNRCA, propose using the familiar concept of a prescription to help physicians incorporate exercise recommendations into their routine practice. In the journal American Family Physician, McDermott and Mernitz provide clinicians with explicit guidelines for giving their older patients effective "exercise prescriptions."

Their motto for determining an exercise prescription is FITT-PRO:

• -Frequency
• -Intensity
• -Type
• -Time
• -Progression

According to FITT-PRO principles, an exercise prescription must explicitly instruct the patient regarding what type of exercise to do, how often, how hard, and for how long. The exercises must also progress over time as the patient becomes more physically fit. McDermott and Mernitz caution that, as with medication prescriptions, these exercise parameters must be personalized to suit each patients health status and goals.

McDermott, who is also a licensed nutritionist, points out that fewer than half of older adults report ever having received a suggestion to exercise from their physicians. "Clinicians shouldnt feel like they have to be fitness experts to discuss exercise with their patients," she says. "These guidelines are intended to serve as a how-to manual for health care providers." The article provides sample prescriptions, as well as instructive tables and figures for clinicians to follow in creating individualized exercise prescriptions for their patients.

The authors explain, "There are four ways to improve physical fitness: aerobic exercise, resistance training, flexibility, and lifestyle modification." All programs should include combinations of these types of activities, and be tailored toward the individuals fitness goals. "For example," McDermott says, "when the goal is to improve functional capacity in activities of daily living, a cross-training program emphasizing the core muscle groups of the back, thighs, and abdomen is preferred."

"Only 30 percent of Americas senior citizens engage in regular exercise," notes McDermott, "yet there is compelling evidence suggesting that people in all conditions of health and at all fitness levels benefit from regular physical activity. In fact, the most de-conditioned individuals have the greatest and fastest response." Mernitz adds, "Seniors tend to have less access than other demographic groups to physical activity information and programming. In contrast, they have relatively more contact with their health care providers."

"Starting an exercise program later in life can significantly modify risk factors, even if a person has been sedentary in prior years," McDermott concludes. "Health care providers can play a major role in offering effective and inexpensive primary or adjunct therapies, encourage appropriate physical activity, and dispel myths that persist as barriers to exercise in the elderly."

Among the useful resources McDermott and Mernitz reference is a book created by colleagues at the John Hancock Center for Physical Activity and Nutrition at the Friedman School of Nutrition Science and Policy at Tufts University, along with experts from the Centers for Disease Control and Prevention ( CDC). The book (citation below), available as a PDF on the CDC web site, is called Growing Stronger: Strength Training for Older Adults, and contains detailed explanations and useful illustrations of strength-training exercises. It is intended to help seniors make strength training part of a regular exercise routine.

McDermott AY, Mernitz H. American Family Physician. (August 1) 2006; 74(3). "Exercise and Older Patients: Prescribing Guidelines."

Seguin RA, Epping JN, Buchner DM, Bloch R, Nelson M. Growing Stronger: Strength Training for Older Adults. 2002. Also available at: http://www.cdc.gov/nccdphp/dnpa/physical/growing_stronger/growing_stronger.pdf

Genes and Diet Linked to Risk Factors for Heart Disease

Researchers from the Jean Mayer USDA Human Nutrition Research Center (USDA HNRCA) at Tufts University and colleagues have found another link among genes, heart disease and diet. The study, published in Circulation, examined apolipoprotein A5 (APOA5), a gene that codes for a protein, which in turn plays a role in the metabolism of fats in the blood. The results show that people who carry a particular variant of APOA5 may have elevated risk factors that are associated with heart disease, but only if they also consumed high amounts of omega-6 fatty acids in their diets.

Corresponding author Chao-Qiang Lai, PhD, a USDA-Agricultural Research Service ( ARS) scientist at the USDA HNRCA, and colleagues analyzed lipid levels and dietary assessment questionnaires of more than 2,000 participants in the Framingham Heart Study and quantified their intake of different types of fats.

Omega-6 fatty acids, as well as omega-3 fatty acids, are polyunsaturated fatty acids (PUFAs) and, according to a report from the National Institutes of Health Office of Dietary Supplements, most Americans consume about 10 times more omega-6s than omega-3s. Omega-3s are found in nuts, leafy green vegetables, fatty fish, and vegetable oils like canola and flaxseed, while omega-6s are found in grains, meats, vegetable oils like corn and soy, and also processed foods made with these oils. Both omega-3s and omega-6s, known as essential fatty acids, must be consumed in the diet because they are not made by the body.

"We know that some people are genetically predisposed to risk factors for heart disease, such as elevated low-density lipoprotein levels in the blood," says Lai, "and that APOA5 has an important role in lipoprotein metabolism. We wanted to determine if certain dietary factors change the role of APOA5 in metabolizing these lipoproteins and their components, such as triglycerides."

Lai and colleagues found that approximately 13 percent of both men and women in the study were carriers of the gene variant. Those individuals that consumed more than six percent of daily calories from omega-6 fatty acids displayed a blood lipid profile more prone to atherosclerosis (hardening of the arteries) and heart disease, including higher triglyceride levels.

Jose Ordovas, PhD, senior author of the study and director of the Nutrition and Genomics Laboratory at the USDA HNRCA, notes that "previous research points to polyunsaturated fatty acids like omega-3s and omega-6s as good fats, thought to reduce risk of heart disease by lowering cholesterol levels if used in place of saturated fats that are mostly found in animal sources."

Ordovas continues, "Research hasnt shown us yet if there is an optimal ratio for omega- 3s to omega-6s, or if consuming a certain amount of omega-6s might negate the benefits of omega-3s. We do know that omega-6s are necessary for the body and can be a source of healthful fat in the diet, but for the 13 percent who are carriers of the particular APOA5 gene variant, consuming fewer omega-6s in relation to omega-3s may be important, as it might help reduce the risk of developing precursors to heart disease."

The carriers of the variant who ate more than six percent of total calories from omega-6s had a 21 percent increase in triglyceride levels, as well as an approximately 34 percent elevation of certain atherogenic lipoprotein particles in the blood.

Carriers who consumed less than six percent of total calories from omega-6s did not show a significant increase in the lipid levels that are risk factors for heart disease. In contrast to omega-6s, higher consumption of omega-3s decreased triglyceride and atherogenic lipoprotein particle levels in the blood, regardless of a persons APOA5 gene variant.

Although the researchers analyzed information on several types of dietary fat, including saturated fat and monounsaturated fat, the interactions between diet and APOA5 were seen only with PUFAs, "adding evidence to the prominent role of PUFAs as modulators of genetic effects in lipid metabolism," write the authors. They go on to explain that "a more complete understanding of these factors and a thoughtful use of this information should help in the identification of vulnerable populations who will benefit from more personalized dietary recommendations."

A second study published by Ordovas, Lai, and colleagues in the Journal of Lipid Research also studied variants of the APOA5 gene in participants in the Framingham Heart Study to determine if the gene is related to atherosclerosis. The authors, including corresponding author Christopher ODonnell of the National Heart, Lung, and Blood Institutes Framingham Heart Study, and first author Roberto Elosua, a former Fulbright-Generalitat de Catalua fellow who works with Ordovas, found that while most variants of the APOA5 gene were not associated with carotid intimal medial thickness (IMT), a surrogate measure of atherosclerosis burden, particular gene variants were "significantly associated with carotid IMT in obese participants."

Carriers of the particular gene variants who were obese expressed the effects of the gene variant differently than carriers who were not obese, showing a greater build-up of plaque in the heart. This was true for participants who were obese regardless of fat and cholesterol levels in the blood, age, gender, smoking or diabetes status, weight-for-height and blood pressure, all factors which are thought to influence risk of heart disease. Lai notes that "although obesity is a known contributing factor to heart disease, the association was strengthened in carriers of the rare APOA5 variant who were obese."

"It may be more important for some people to make preventive dietary and lifestyle changes than others, depending on their genetic makeup," says Ordovas. "The bad genotype, in this study, doesnt seem to be that bad unless its triggered by obesity," he concludes. "The observations, while strong, should be considered with caution and confirmed in other studies. Also, the findings were restricted to a Caucasian cohort and may not be generalizable to other ethnic cohorts."

The Agricultural Research Service (ARS) is the U.S. Department of Agricultures chief scientific research agency.

Lai CQ, Corella D, Demissie S, Cupples A, Adiconis X, Yueping Z, Parnell LD, Tucker KL, Ordovas JM. Circulation (May 2) 2006;113: 2062 2070. "Dietary Intake of n-6 Fatty Acids Modulates Effect of Apolipoprotein A5 Gene on Plasma Fasting Triglycerides, Remnant Lipoprotein Concentrations, and Lipoprotein Particle Size: The Framingham Heart Study."

Elosua R, Ordovas JM, Cupples LA, Lai CQ, Demissie S, Fox CS, Polak JF, Wolf PA, DAgostino RB, ODonnell CJ. Journal of Lipid Research (May ) 2006;47: 990-996 "Variants at the APOA5 locus, association with carotid atherosclerosis, and modification by obesity: the Framingham Study."

If you are interested in learning more about these topics, or speaking with a faculty member at the Friedman School of Nutrition Science and Policy at Tufts University, or another Tufts health sciences researcher, please contact Siobhan Gallagher at 617-636-6586 or Peggy Hayes at 617-636-3707.

The Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy at Tufts University is the only independent school of nutrition in the United States. The school's eight centers, which focus on questions relating to famine, hunger, poverty, and communications, are renowned for the application of scientific research to national and international policy. For two decades, the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University has studied the relationship between good nutrition and good health in aging populations. Tufts research scientists work with federal agencies to establish the USDA Dietary Guidelines, the Dietary Reference Intakes, and other significant public policies.