Nutrition Updates

GARLIC AND CANCER RISK

Kim JY and Kwon O. Garlic intake and cancer risk: an analysis using the Food and Drug Administration's evidence-based review system for the scientific evaluation of health claims. Am J Clin Nutr. 2009;89:257–264.

Garlic contains high levels of organosulfur compounds and flavonoids and is thought to provide a number of health benefits, including reduction of cancer risk. While some research shows an inverse relationship between garlic and cancer risk in humans, Food and Drug Administration (FDA) regulations require health claims related to a food product to be substantiated via an evidence-based review system. Kim and Kwon evaluated the available scientific evidence regarding the relationship between garlic intake and risk for different types of cancer using the FDA's evidence-based review system for the purpose of establishing the validity of health claims for garlic.

Literature searches were conducted for Allium sativum, vegetables, diet, and nutrition in conjunction with cancer, neoplasm, and individual cancers such as gastric or renal cell cancer. Searches were limited to articles published on human studies written between 1955 and 2007 and written in Korean or English. Nineteen studies were selected and were evaluated for factors including methodological quality, study type, and overall consistency of the total body of evidence. Using the FDA methodology, there was no evidence for reduction in risk for gastric, breast, lung, or endometrial cancers with garlic intake. There was limited evidence for a reduction in risk for colon, prostate, esophageal, larynx, oral, ovarian, and renal cell cancers with garlic intake. The authors provide recommended wording for food labels to convey health claims related to garlic intake and cancer risk.

Comment: Dr. Rivlin asserts that garlic has been used in a medicinal capacity for millennia. Garlic is known to contain a number of compounds with anticancer properties, including allylsulfides and selenium. Although allium derivatives have shown promise in animal trials, Dr. Rivlin suggests that evidence in humans may be limited by the number of sound trials available for inclusion in an evidence-based review; he argues that the present review be considered an incentive for further investigation into the possible role of garlic on cancer prevention.

Comment: Rivlin RS. Can garlic reduce risk of cancer? Am J Clin Nutr. 2009;89:17–18.

FLAVONOID INTAKE AND COGNITIVE PERFORMANCE IN THE ELDERLY

Nurk E, Refsum H, Drevon CA, Tell GS, Nygaard HA, Engedal K, and Smith AD. Intake of flavonoid-rich wine, tea, and chocolate by elderly men and women is associated with better cognitive test performance. J Nutr. 2009;139: 120–127.

Polyphenols from plant-derived foods function as antioxidants, and their role in human health is only beginning to be understood. Diets that include foods such as wine, tea, chocolate, and fruits are high in polyphenols, particularly flavonoid compounds, and intake of flavonoids is associated with reduced age-related risk for dementia and cognitive decline. A cognitive substudy was added to the Hordaland Health Study (HUSK) with the objective of determining the degree to which intake of chocolate, wine, and tea affected cognitive ability in a cross-section of healthy, free-living elders.

The cognitive study included 2031 Norwegians between the ages of 70 and 74 years (55% female). Participants took a variety of cognitive tests designed to assess a broad range of cognitive domains, including spatial ability, learning and memory, attention, and verbal fluency. Cognitive scores were compared with diet both individually and as a combined, global cognitive score. Dietary intakes were assessed with a food frequency questionnaire appropriate to Norwegian food patterns. Cognitive performance was dose-dependently higher in those consuming up to 10 g/d of chocolate and up to ∼75–100 ml/d of wine, and effects were stronger for wine. These effects were most pronounced for individuals consuming all three foods. The authors suggest there may be an additive relationship among tea, wine, and chocolate in the maintenance of cognitive functioning in older individuals. These data are important as nutrients are frequently studied in isolation; however, the effects of a given nutrient may be dependent upon other components of the overall diet. Although causality cannot be determined from food-based analyses of population data, the present study indicates that more research on the bioactive compounds in flavonoid-rich foods has merit.

POTASSIUM BICARBONATE AND BONE HEALTH

Dawson-Hughes B, Harris SS, Palermo NJ, Castaneda-Sceppa C, Rasmussen HM, and Dallal GE. Treatment with potassium bicarbonate lowers calcium excretion and bone resorption in older men and women. J Clin Endocrinol Metab. 2009;94:96–102.

Calcium and vitamin D have been studied extensively with respect to bone loss; however, there is evidence that the acid/base balance of the diet is also important. A high-acid milieu can affect bone health via decreases in bone growth and increases in bone. Overall, the American diet, which is high in cereal grains and protein, tends to be acidogenic with high-protein diets resulting in increased calcium output in the urine (calciuria). Acidosis can be offset by supplementation with alkaline salts, such as potassium bicarbonate, although previous work has not clearly shown whether potassium or bicarbonate provides the most benefit. Diets rich in fruits and vegetables provide potassium, and also are alkali-producing via metabolism to bicarbonate. Increased potassium intake is associated with reduced calcium output and with higher bone mineral density. Bicarbonate levels are also associated with decreased calcium output, and are associated with reduced markers of bone resorption. To better understand the role of potassium and bicarbonate in maintaining bone health, Dawson-Hughes et al. studied the effects of three months of treatment with 67.5 mmol/d potassium (as KCl), bicarbonate (as NaHCO₃), potassium bicarbonate (KHCO₃), or placebo on markers of bone turnover and resorption.

The 171 male (n = 76) and female (n = 95) participants aged 50 years and above were randomized into one of the four treatment conditions. Primary outcomes included changes in net acid excretion, urinary N-telopeptide (a marker for bone resorption) and calcium output, and serum osteocalcin. Supplementation with bicarbonate decreased calciuria and lowered N-telopeptide, indicating a reduction in bone resorption. In comparison with no bicarbonate, net acid excretion was significantly reduced following bicarbonate administration, suggesting a reduction in acid load. Moreover, there was a linear relationship between changes in net acid excretion and changes in calciuria and excretion of N-telopeptide, which indicates that increasing alkali intake can lower bone loss. Supplementation with potassium did not affect calciuria or bone turnover. The authors suggest that increasing dietary alkali intake can be a cost-effective approach to reducing bone loss in older individuals.

HIGH-DOSE DOCOSAHEXAENOIC ACID AND NEURODEVELOPMENT IN PRETERM INFANTS

Makrides M, Gibson RA, McPhee AJ, Collins CT, Davis PG, Doyle LW, Simmer K, Colditz PB, Morris S, Smithers LG, Willson K, and Ryan P. Neurodevelopmental outcomes of preterm infants fed high-dose docosahexaenoic acid: a randomized controlled trial. JAMA. 2009;301:175–182.

Docosahexaenoic acid (DHA) plays major functional and structural roles in brain development, and DHA accretion in the brain is greatest during the final trimester of pregnancy. During this time, whole-body accretion of DHA exceeds 50 mg/kg/d, which is comparable to dietary levels of 1% of total fatty acids. Preterm infants, born prior to 33 weeks’ gestation, are at risk for poorer mental development and subsequent mental performance in comparison with full-term infants. Based on DHA accretion, preterm infants fed standard levels of DHA in formula or who rely on breast milk (0.2%–0.35% of total fatty acids) may not receive adequate DHA for brain development. The present trial by Makrides et al. evaluated the effect of providing ∼1% DHA on neurodevelopment at 18 months of age.

The high-DHA intervention was achieved by increasing the amount of DHA in breast milk by supplementing the mothers with 3 g/d of tuna-oil capsules and/or a high-DHA formula. The mothers in the no-intervention group received soy-oil capsules and/or the infants were fed standard preterm formula. The high-DHA intervention continued until the estimated expected date of delivery. The primary outcome was performance on the Mental Development Index of the Bayley Scales of Infant Development at 18 months. Future assessment of these children at age 7 is planned. A total of 614 infants were included in the present analysis. In the overall analysis, there were no effects of high-DHA supplementation on cognitive performance at 18 months. Planned subgroup analysis showed that high-DHA supplementation was associated with significantly better performance for girls, but not for boys. Additionally, there was a tendency for DHA supplementation to produce positive effects on cognition in the smallest infants (birth weight <1250 g), but this difference was not significant following adjustment for covariates. The finding that high-DHA supplementation was effective only in girls was unexpected. The authors posit that because girls have a higher synthetic capacity for endogenous DHA, their increased synthesis coupled with supplemental DHA was adequate for their needs. Preterm boys, therefore, could require higher amounts of DHA to show a benefit. The present data suggest that the current standard feeding practices for preterm infants may provide insufficient levels of DHA for optimal neurodevelopment, and that increasing DHA to 1% of total fatty acid content may be beneficial for brain function in preterm girls.

VITAMIN C AND BLOOD PRESSURE IN YOUNG WOMEN

Block G, Jensen CD, Norkus EP, Hudes M, and Crawford PB. Vitamin C in plasma is inversely related to blood pressure and change in blood pressure during the previous year in young Black and White women. Nutr J. 2008;7: doi:10.1186/1475-2891-7-35.

High blood pressure remains highly prevalent in the United States with an estimated 60% of adults having hypertension or pre-hypertension; it is also a risk factor for cardiovascular and kidney disease. Changing to a diet that is rich in fruits and vegetables and low in fat and sodium, such as the Dietary Approaches to Stop Hypertension (DASH) diet, reduces blood pressure; for this reason, the DASH diet is recommended by government and medical groups for reducing or preventing hypertension. Because the DASH diet is high in fruits and vegetables, it is rich in vitamin C. Vitamin C may play a role in reducing or preventing hypertension via interactions with endothelium-derived nitric oxide, which is important for maintaining vascular tone and reactivity. Previous studies have shown an inverse relationship between blood pressure and plasma vitamin C levels in older individuals with elevated blood pressure. In the research described here, Block et al. examined the relationship between plasma vitamin C levels and blood pressure in young women.

Participants (N = 242) were recruited from the Growth and Health Study, a 10-year trial designed to investigate the development of obesity in girls during adolescence. Black (n = 155) and white (n = 87) girls were enrolled between the ages of 8 and 11 years of age and followed through the ages of 18–21. Blood pressure measurements from the penultimate (year 9) and from the final follow-up year (year 10) were analyzed as a function of plasma vitamin C levels taken at year 10. Primary outcomes were blood pressure at year 10 and change in blood pressure from year 9 to year 10. Plasma vitamin C was significantly inversely associated with blood pressure in this population. For each 1 mg/dL increase in plasma vitamin C levels, systolic blood pressure was 4.1 mmHg lower and diastolic blood pressure was 4.0 mmHg lower. Moreover, plasma vitamin C was significantly inversely related to change in blood pressure, with the women in the highest quartile showing little change over time. Although diet and supplement intakes are not reported in this paper, the authors indicate that the range of plasma vitamin C levels in the young women would be seen with dietary intake, but that the values in the highest quartile likely represent significant contribution from supplemental vitamin C. The investigators propose that trials investigating the long-term treatment effects of vitamin C on blood pressure regulation are warranted.