HIGH ADHERENCE TO MEDITERRANEAN DIET SLOWS COGNITIVE DECLINE
Féart C, Samieri C, Rondeau V, Amieva H, Portet F, Dartigues JF, Scarmeas N, and Barberger-Gateau P. Adherence to a Mediterranean diet, cognitive decline, and risk of dementia. JAMA. 2009; 302:638–648.
Following a traditional Mediterranean diet is associated with reduced risk for cardiovascular disease, cancer, and diabetes. It is proposed that the Mediterranean diet may also be protective against cognitive decline in aging, due to the diet's rich content of omega-3 fatty acids, B vitamins, and antioxidants and its low content of saturated fats. The present longitudinal study examined the protective effects of following a Mediterranean diet on cognitive performance in elderly French individuals.
Participants were selected from individuals enrolled in the Three-City study (3C) conducted in Bordeaux, Dijon, and Montpellier, France. Participants (N = 1410) who were at least 65 years of age were enrolled between 2001 and 2002 and followed for up to 5 years. Adherence to a Mediterranean-style diet was determined using 24-h food recalls and food frequency questionnaires. Intakes of foods aligned with a Mediterranean pattern were scored and a total adherence score of 0–9 (9 indicates greatest adherence) were assigned to participants. Primary outcome measures included change in Mini Mental State Examination (MMSE) scores, assessing global performance, and tests assessing semantic memory, visual memory, and verbal memory. Additionally, participants were evaluated for dementia using neuropsychological test scores and examination by a neurologist. Greater adherence with a Mediterranean diet was associated with a slower rate of decline on the MMSE but not on other cognitive tests. Incidence of dementia was not affected by adherence to the dietary pattern. The authors suggest that adherence to a Mediterranean diet may be of benefit in the long prodromal phase of dementia, but may confer less benefit as the onset of dementia approaches.
Comment: In his editorial, Dr. Knopman discusses the above study by Féart et al. and a second trial in the same issue of JAMA that reported a link between higher adherence with a Mediterranean diet and reduced risk for Alzheimer's disease. When looking at cognitive decline in the elderly, it is important to consider contributions not only from the diet over the lifespan but from other health-related behaviors as well. Moreover, adherence to a Mediterranean diet may exert primary effects on the maintenance of cognitive performance via reduction of cardiovascular and cerebrovascular disease. In support of this is the observation that in the study of Féart et al., the benefits of a Mediterranean diet on MMSE scores were mitigated when stroke was entered into the model. Dr. Knopman urges restraint in interpreting the present studies and their translation into public health recommendations.
Comment: Knopman DS. Mediterranean diet and late-life cognitive impairment: a taste of benefit. JAMA. 2009; 302:686–687.
VITAMIN D STATUS AND CARDIOVASCULAR RISK FACTORS IN ADOLESCENTS
Reis JP, von Mühlen D, Miller ER 3rd, Michos ED, and Appel LJ. Vitamin D status and cardiometabolic risk factors in the United States adolescent population. Pediatrics. 2009 doi:10.1542/peds.2009-0213
Vitamin D deficiency in adulthood is associated with increased risk for cardiovascular disease, metabolic syndrome, hypertension, and diabetes. In younger people, the importance of vitamin D in bone health is well-understood, but the role of vitamin D in cardiovascular risk factors is less well understood. The present study by Reis et al. examined the relationship between serum vitamin D levels and metabolic syndrome and other risk factors for cardiovascular disease. Data were extracted from the 2001–2004 National Health and Nutrition Examination Survey (NHANES).
A sample of 3528 adolescents between the ages of 12 and 19 years was used in the analysis. Measurements included serum 25-hydroxyvitamin D, blood glucose, waist circumference, blood pressure, blood lipids, and BMI. Mean 25-hydroxyvitamin D levels were in the mildly deficient range (24.8 ng/mL; reference value for optimal levels: 32–100 ng/mL ) and was lowest in black youths (15.5 ng/mL) and highest in white youths (28.0 ng/mL). Lower levels of vitamin D were associated with overweight and abdominal obesity, higher blood pressure, higher blood glucose, and metabolic syndrome. When adjusted for obesity, the associations between lower levels of vitamin D and hyperlipidemia, hyperglycemia, and metabolic syndrome remained significant. While the data from this study cannot give an indication as to the number of vitamin D-deficient young individuals who will develop cardiovascular disease later in life, they provide a target for nutritionally modifiable cardiovascular risk factors in young people.
OILY FISH INTAKE AND INSULIN SENSITIVITY IN IRON-DEFICIENT WOMEN
Navas-Carretero S, Pérez-Granados AM, Schoppen S, and Vaquero MP. An oily fish diet increases insulin sensitivity compared to a red meat diet in young iron-deficient women. Br J Nutr. 2009; 102:546–553.
Dietary advice for women with, or at risk for, iron deficiency has typically encouraged intake of heme iron found in red meat. Some observations, however, suggest that iron overload may produce metabolic abnormalities linked with glucose regulation and cardiovascular disease. Additionally, inverse associations between iron stores and insulin sensitivity have been observed in individuals consuming a red-meat diet in comparison to an ovo-lacto vegetarian diet. In related research, Navas-Carrtero et al. have shown that intake of fish rich in omega-3 fatty acids improves absorption of iron from plant sources. Taken together, the above observations have led to the proposal that intake of fatty fish may be of benefit in cases of insulin sensitivity in iron-deficient individuals.
To test this hypothesis, 25 young iron-deficient women were given two diets in a study with a randomly assigned crossover design. The participants (ages 18–30 years) had low iron levels (<20 ng/mL) but normal blood glucose, blood lipid, and insulin levels. The two diets were identical except for their meat and fish content. The red meat diet contained five portions of red meat, one portion of lean fish, two portions of poultry, and two eggs per week. The oily fish diet contained two portions of salmon, two portions of water-packed tuna, one portion of sardines, one portion of lean fish, two portions of poultry, and two eggs per week. Diets were given for 8 weeks with all participants receiving both diets. Primary outcome measures included blood lipid profiles, insulin sensitivity, and fasting blood glucose and insulin levels. Insulin sensitivity and HDL cholesterol increased significantly and insulin levels decreased significantly in subjects on the oily fish diet. In a related study, there were no significant differences in iron status between individuals receiving the red meat and the oily fish diets. However, the authors suggest that increasing oily fish consumption may have a positive effect on cardiovascular risk factors in an iron-deficient population.
ANTIOXIDANT SUPPLEMENTS LITTLE HELP IN REDUCING RISK OF TYPE 2 DIABETES
Song Y, Cook NR, Albert CM, Van Denburgh M, and Manson JE. Effects of vitamins C and E and beta-carotene on the risk of type 2 diabetes in women at high risk of cardiovascular disease: a randomized controlled trial. Am J Clin Nutr. 2009; 90:429–437.
Diets rich in antioxidant vitamins are associated with reduced risk for the development of type 2 diabetes and cardiovascular disease. In animal models, supplementation with antioxidants slows the development of diabetes, and some short-term trials in diabetic humans show that high-dose antioxidant supplements have a positive effect on oxidative stress, lipid metabolism, and glucose handling. However, few trials have examined the ability of long-term antioxidant supplementation to slow or prevent the development of diabetes in individuals at high risk. In the present analysis, Song et al. report on the efficacy of supplementation with vitamins C and E and beta-carotene in the primary prevention of type 2 diabetes.
Participants (N = 6574) were enrolled in the Women's Antioxidant Cardiovascular Study (WACS), which ran from 1995 to 2005. The trial was originally designed to evaluate the effect of antioxidant vitamin supplements on the development of cardiovascular disease in women at high risk for cardiovascular disease. Participants reported on in the present paper were free of diabetes at the onset of the study, and the paper represents a secondary analysis of the data from the WACS trial. Women were randomly assigned to receive antioxidant supplements or placebo. Vitamin C (500 mg/d), vitamin E (600 IU every other day), and beta-carotene (50 mg every other day) were given individually or in combination (see original manuscript for full description of all eight experimental conditions). Primary outcome measures for this analysis included self-reported diagnosis of diabetes and supplementary questionnaires on diabetic symptoms. Participants were followed for an average of 9.2 years. Over the trial period, 895 participants developed diabetes. Although no observations reached significance, there was a trend for reduced risk following supplementation with vitamin C relative to placebo and a trend for increased risk following vitamin E supplementation. There were no observed associations between supplementation with beta-carotene and risk for diabetes. However, all of these trends must be viewed with caution as none of the observations were statistically significant, and the original trial was powered and designed to assess cardiovascular disease outcomes rather than incidence of diabetes. The authors conclude there is no support for recommending antioxidant supplementation for the primary prevention of type 2 diabetes.
Comment: Drs. Meydani and Azzi raise the important point that lifestyle variables such as dietary modification, weight loss, and increased physical activity are important means of both modifying and preventing progression of type 2 diabetes and cardiovascular disease. They highlight the general paucity of evidence to support the use of high-dose antioxidant supplements in the development of diabetes. Limitations in our understanding of the role of antioxidants in diseases purported to be related to oxidative stress include the observations that antioxidant nutrients may have vastly different effects in vivo in comparison to in vitro. Moreover, they caution that by focusing on only one aspect of type 2 diabetes (oxidative stress) the greater issue of chronic inflammation becomes obscured. Their recommendation is to focus on reduction of body weight/adiposity through reducing caloric intake and increasing physical activity rather than looking to antioxidant supplements to lower risk for developing type 2 diabetes.
Comment: Meydani M and Azzi A. Comment Diabetes risk: antioxidants or lifestyle? Am J Clin Nutr. 2009; 90:253–254.