Nutrition Note: Fall 2007

Zinc May Reduce Pneumonia Risk in Nursing Home Elderly

BOSTON — When elderly nursing home residents contract pneumonia, it is a blow to their already fragile health. Simin Nikbin Meydani, DVM, PhD, of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University and colleagues report that maintaining normal serum zinc concentration in the blood may help reduce the risk of pneumonia development in that population.

"Based on our data, it appears that daily zinc intake can help nursing home residents who are susceptible to pneumonia, especially those with low serum zinc concentrations in their blood," says Meydani, corresponding author and director of the Nutritional Immunology Laboratory at the USDA HNRCA. "The study participants with normal serum zinc concentrations in their blood reduced their risk of developing pneumonia by about 50 percent. Additionally, deaths from all causes were 39 percent lower in this group."



Meydani and colleagues analyzed blood samples from a previous study that investigated the role of vitamin E in preventing respiratory infections in nursing home residents ages 65 and older. The study enrolled 617 men and women from 33 nursing homes in the Boston area. All of the participants received daily supplements containing 50 percent of the recommended dietary allowance of several vitamins and minerals, including zinc, for one year. Foods that provide zinc include oysters, red meat, poultry, whole grains, beans and dairy products.

In the present study, published in the October issue of the American Journal of Clinical Nutrition, the authors compared blood samples collected at the beginning and the conclusion of the one-year study. The participants whose serum zinc concentrations remained low throughout that 12-month period had more difficulty battling pneumonia. "Not only did those participants have a higher risk of developing pneumonia when they did become sick, they did not recover as quickly and required a longer course of antibiotics," says Meydani, who is also a professor at the Friedman School of Nutrition Science and Policy and the Sackler School of Graduate Biomedical Sciences, both at Tufts University. "We also noted a higher rate of death from all causes."

Maintaining normal serum zinc concentration in the blood throughout the 12-month study period benefited the participants even if they did develop pneumonia. Meydani adds, "Those participants with normal serum zinc concentrations in their blood were more likely to spend fewer days on antibiotics and recover more quickly."

Meydani and colleagues conclude that zinc may reduce the risk of pneumonia, and its associated complications in nursing home residents. "Zinc is already known to strengthen the immune system; however, there needs to be further investigation of zinc and its effect on pneumonia development and prevention in nursing homes," Meydani says. "The next step would likely be a clinical trial."

The study was supported by the U.S. Department of Agriculture Agricultural Research Service and by grants from the National Institutes of Health and, for the preparation of the study capsules, Hoffmann-La Roche Vitamins and Fine Chemicals Division (currently DSM Nutritional Products).

Meydani SM, , Barnett  JB, Dallal ,GE, Fine BC, Jacques PF, Leka LD, and Hamer, DH.

American Journal of Clinical Nutrition. 2007; 86: 1167-1173. "Serum zinc and pneumonia in nursing home elderly".

Limiting Refined Carbohydrates May Stall AMD Progression



BOSTON — Eating fewer refined carbohydrates may slow the progression of age-related macular degeneration (AMD), according to a new study from researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.

AMD results in partial or total blindness in 7 to 15% of the elderly, according to the Eye Diseases Prevalence Research Group. "Dietary changes may be the most practical and cost-effective prevention method to combat progression of AMD," says Allen Taylor, PhD, director of the Laboratory for Nutrition and Vision Research at the USDA HNRCA. "It is surprising there is so little attention focused on the relationship between AMD and carbohydrates."

The current study, published in the October issue of the American Journal of Clinical Nutrition, builds on a recent analysis by Taylor and colleagues that found men and women older than 55 who consumed diets with higher-than-average dietary glycemic index foods appeared to have an increased risk for both early and later stages of AMD.

Dietary glycemic index is a scale used to determine how quickly carbohydrates are broken down into blood sugar, or glucose. Foods with a high glycemic index are associated with a faster rise and subsequent drop in blood sugar. Refined carbohydrates like white bread and white rice have high glycemic indices. Whole wheat versions of rice, pasta and bread are examples of foods with low glycemic indices.

In the present study, Taylor and colleagues analyzed diet questionnaires completed by 4,757 non-diabetic men and women participating in the nationwide Age-Releated Eye Disease Study (AREDS). The eight-year AREDS study enrolled participants between the ages of 55 and 80 with varying stages of AMD. Taylor and colleagues examined the participants' carbohydrate intake over a one-year period and used the data to calculate the participants' dietary glycemic index.

"Our data showed those people in the high-glycemic-index group were at greater risk of AMD progression, especially those already in the late stages," says first author Chung-Jung Chiu, DDS, PhD, scientist in the Laboratory for Nutrition and Vision Research at the USDA HNRCA and assistant professor at Tufts University School of Medicine. "Participants who consumed the most refined carbohydrates were 17 percent more likely to develop blinding AMD than the group that consumed the least."

According to the authors, public health officials believe the condition could spur a public health crisis in the United States by 2020, when they predict the cases of AMD-related vision loss will have doubled to three million.

"No one has been able to identify an effective noninvasive intervention that will slow the progression of AMD" says Taylor, who is also a professor at the Friedman School of Nutrition Science and Policy at Tufts and Tufts University School of Medicine. "We feel we have identified a risk factor that could postpone the debilitating loss of vision with very little economic or personal hardship. Based on our data, limiting refined carbohydrate intake, such as by limiting sweetened drinks or exchanging white bread for whole wheat, in at-risk elderly could reduce the number of advanced AMD cases by 8 percent in five years.  This can equate to saving the sight of approximately 100,000 people."

The authors note that their findings warrant randomized controlled clinical trials.

The study was supported by the U.S. Department of Agriculture Agricultural Research Service and by grants from the National Institutes of Health, Johnson and Johnson Focused Giving Program, and the American Health Assistance Foundation.

Chiu C-J, Milton RC, Klein R, Gensler G, and Taylor A. American Journal of Clinical Nutrition. 2007 ; 86: 1210-1218. "Dietary carbohydrate and the progression of age-related macular degeneration: a prospective study from the Age-Related Eye Disease Study."

Glycemic Index Values are Variable, Report Researchers

BOSTON —In work investigating the reproducibility of glycemic index values, researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (USDA HNRCA) have reported that multiple glycemic index value determinations (measure of the rate of glucose absorption into the bloodstream) using a simple test food, white bread, resulted in a relatively high level of inter-individual (among different individuals), and intra-individual (within the same individual) variability. Further studies will focus on better defining the magnitude and the sources of the variability. The intent is to better understand how glycemic index relates to chronic disease risk in a wide range of individuals.

Alice Lichtenstein, DSc, corresponding author and director of the Cardiovascular Nutrition Laboratory at the USDA HNRCA and colleagues assessed 14 study participants' glycemic response to 50 grams of carbohydrate in the form of white bread (test food) and glucose dissolved in water (control food) on different days. This experiment was repeated three times with each individual.

"Using glucose as the control food, previous studies indicate that white bread has a glycemic index of about 70," says Lichtenstein, who is also the Gershoff professor of nutrition science and policy at the Friedman School of Nutrition Science and Policy at Tufts. "In our study the combined average was 71, virtually identical to the published value. However, quite strikingly, individual values ranged from 44 to 132. What is critical is to determine why there is such a wide range of responses among individuals.

In addition, within the same individual, test values varied by as much as 42 percent. "These results show that perhaps using glycemic index for groups is a reasonable indicator to predict chronic disease risk, but there is still considerable uncertainty when applying glycemic index to individuals," explains Lichtenstein.

Glycemic index is a scale applied to foods based on how quickly the glucose in foods is absorbed into the blood stream, relative to pure glucose. Some nutrition professionals use the glycemic index as a tool for people trying to control blood sugar, such as those with diabetes. Others use the mean glycemic index of diets to predict chronic disease risk in large groups of people. Potential confounding factors, such as the fiber or fat content of the food, are not directly factored into the calculations.

"There are many factors that can influence the glycemic index of a food," says Lichtenstein. "For example, a piece of white bread may have a high glycemic index but, if a person eats a slice of turkey and cheese with that bread, the effect of the multiple foods may result in a different glycemic index than if that person had eaten the white bread alone. Since most food is consumed as combinations during meals and snacks, there is a need to assess the significance of using glycemic index values determined on individual foods for food mixtures. Similarly, it is important to know whether the food consumed prior to a meal or snack alters subsequent glycemic response.

It is possible that we need to develop better research tools and more stringent applications for glycemic index determinations," she says. "Larger studies of diverse populations are needed to determine why inter-individual, and particularly intra-individual, glycemic index values are so variable. If we can identify the source of the variability, it will allow for more insight into the applications of the glycemic index as a tool for both researchers and in public health messages."

Lichtenstein and colleagues have received a five-year grant from the National Institute of Diabetes and Digestive and Kidney Diseases to further their understanding of the glycemic index and its utilities. The current study was supported by the U.S. Department of Agriculture's Agricultural Research Service.

Vega-Lopez S, Ausman LM, Griffith JL, Lichtenstein AH. Diabetes Care. 2007 (June); 30 (6): 1412-1417. "Interindividual Variability and Intra-Individual Reproducibility of Glycemic Index Values for Commercial White Bread."

Sugary Drinks, not Fruit Juice, May Be Linked to Insulin Resistance

BOSTON  — Steady increases in consumption of sugar-sweetened beverages over the last several decades, as well as rates of Type 2 diabetes mellitus, led nutritional epidemiologists at the Jean Mayer USDA Human Nutrition Research Center on Aging (USDA HNRCA) at Tufts University to explore the relationship between sugar-sweetened beverage consumption and insulin resistance, a precursor to Type 2 diabetes. Their findings suggest that higher consumption of sugar-sweetened drinks, but not 100 percent fruit juice, may be associated with insulin resistance, even in otherwise healthy adults.

"Study participants who consumed two or more sugar-sweetened beverages per day had significantly higher fasting blood levels of insulin as compared to participants who did not report consuming any such beverages, regardless of age, sex, weight, smoking status, or other dietary habits," says senior author Paul Jacques, DSc, director of the Nutritional Epidemiology Program at the USDA HNRCA and professor at the Friedman School of Nutrition Science and Policy at Tufts University. "Higher fasting levels of insulin mean these study participants are more at risk for developing Type 2 diabetes. In contrast," he says, "consumption of 100 percent fruit juice was not significantly related to any of our measures of insulin resistance."

Study participants were 2,500 healthy men and women in the Framingham Offspring Study, a community-based study of cardiovascular disease among offspring of people in the original Framingham Heart Study. Participants reported their usual dietary intake for the previous year, which researchers used to determine average intakes of sugar-sweetened drinks (regular and caffeine-free colas and other carbonated beverages containing sugar), diet soft drinks (low-calorie colas with and without caffeine and other low-calorie carbonated beverages), and fruit juice (e.g., apple juice or apple cider, orange juice, and grapefruit juice). One serving of a sugar-sweetened drink or diet soda was considered equivalent to 12 fluid ounces, or a regular-sized can of soda. One serving of fruit juice was considered equivalent to six fluid ounces.

The researchers obtained blood samples from participants who fasted for at least eight hours, and measured the participants' blood levels of insulin as well as glucose. High fasting glucose levels, like high fasting insulin levels, are a pre-cursor to Type 2 diabetes. "Unlike fasting insulin levels, fasting glucose levels were not significantly different between those who consumed sugar-sweetened drinks and those who did not," says Jacques, "However, participants consuming two or more daily servings of 100 percent fruit juice had modestly lower fasting glucose levels, compared with those who did not consume fruit juice." Although this observation might be due to the additional nutrients or other phytochemicals found in the juices, Jacques notes this also may be a consequence of the healthier lifestyle and dietary habits of fruit juice consumers. They were less likely to smoke than non-consumers, and consumed diets relatively lower in saturated fat and higher in total fiber.

Despite these results, Nicola McKeown, PhD, corresponding author and scientist in the Nutritional Epidemiology Program at the USDA HNRCA, does not advise increasing consumption of fruit juice. "While 100 percent fruit juice can be a healthful beverage, too much fruit juice can add excess calories and sugar to the diet. Whole fruit is often a better choice."

Jacques and McKeown also caution that their results cannot be used to determine cause-and-effect relationships among caloric and non-caloric sugar-sweetened beverage consumption and insulin resistance. "It could be that people who drink sugar-sweetened beverages have other unhealthy behaviors that we did not account for," says McKeown.  "Sugar-sweetened drink consumption may prove to be an important determinant of insulin resistance, but more long-term studies of diverse populations that incorporate the use of more direct measures of insulin resistance are needed."  In the meantime, the researchers suggest that people continue to follow the recommendations in the 2005 Dietary Guidelines for Americans, increasing consumption of water while limiting intake of calorically sweetened, nutrient-poor beverages.

This study, published in the September issue of The Journal of Nutrition, was supported by the U.S. Department of Agriculture's Agricultural Research Service; the Framingham Heart Study of the National Heart, Lung, and Blood Institute of the National Institutes of Health; and individual awards from the American Diabetes Association and the American Heart Association.

Yoshida M, McKeown NM, Rogers G, Meigs JB, Saltzman E, D'Agostino R, Jacques PF. Journal of Nutrition. 2007 (September); 137:2121-2127. "Surrogate Markers of Insulin Resistance are Associated with Consumption of Sugar-Sweetened Drinks and Fruit Juice in Middle and Older-Aged Adults."

If you are a member of the media interested in learning more about these topics, or in speaking with a faculty member at the Friedman School of Nutrition Science and Policy at Tufts University, or another Tufts health sciences researcher, Tufts University, or another Tufts health sciences researcher, please contact Andrea Grossman at 617-636-3728 or, via email, 

Andrea.Grossman@tufts.edu, or Christine Fennelly at 617-636-3707, or via email, Christine.Fennelly@tufts.edu.

Tufts research scientists work with federal agencies to establish the USDA Dietary Guidelines, the Dietary Reference Intakes, and other significant public policies. 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.