Dietary glycemic index and retinal microvasculature in adults: a cross-sectional study

Sanchez-Aguadero et al. Nutrition Journal (2016) 15:88 DOI 10.1186/s12937-016-0209-2 SHORT REPORT Open Access Dietary glycemic index and retinal microvasculature in adults: a cross-sectional study Natalia Sanchez-Aguadero1,8*, Rosario Alonso-Dominguez1, Jose I. Recio-Rodriguez2, Maria C. Patino-Alonso3, Manuel A. Gomez-Marcos4, Carlos Martin-Cantera5, Yolanda Schmolling-Guinovart6, Luis Garcia-Ortiz7 and the EVIDENT II Group Abstract Objective: To analyze the relationship between dietary glycemic index (GI) and retinal microvasculature in adults. Methods: This was a cross-sectional study of 300 subjects from the EVIDENT II study. Dietary GI was calculated using a validated, semi-quantitative food frequency questionnaire. Retinal photographs were digitized, temporal vessels were measured in an area 0.5–1 disc diameter from the optic disc and arteriolar-venular index (AVI) was estimated with semi-automated software. Results: AVI showed a significant difference between the tertiles of GI, after adjusting for potential confounders. The lowest AVI values were observed among subjects in the highest tertile of GI, whereas the greatest were found among those in the lowest tertile (estimated marginal mean of 0.738 vs. 0.768, p = 0.014). Conclusions: In adults, high dietary GI implies lowering AVI values regardless of age, gender and other confounding variables. Trial registration: Clinical Trials.gov Identifier: NCT02016014. Registered 9 December 2013. Keywords: Glycemic index, Retinal vessels, Carbohydrates, Microcirculation Background The glycemic index (GI) represents the relative rate at which blood glucose levels rise after consuming 1 g of a carbohydrate-containing food as compared to pure glucose [1]. High GI diets are associated with an increased risk of cardiovascular diseases (CVD) [2]. Accumulating evidence suggests that the development of CVD such as stroke could be predicted by retinal microvascular changes [3]. Retinal microcirculation has been linked to GI in a few studies [4, 5]. This association might be mediated for oxidative stress or inflammation [6–8]. * Correspondence: 1 Primary Care Research Unit, The Alamedilla Health Center, Castilla and León Health Service (SACYL), Biomedical Research Institute of Salamanca (IBSAL), Spanish Network for Preventive Activities and Health Promotion (redIAPP), Salamanca, Spain 8 Primary care Research Unit, The Alamedilla Health Center, Avda. Comuneros N° 27, 37003 Salamanca, Spain Full list of author information is available at the end of the article The purpose of this study was to analyze the relationship of dietary GI with retinal microvasculature in a sample of adults. Methods A cross-sectional study was conducted with 300 subjects, as a sub-analysis of the EVIDENT II trial [9]. The recruitment and data collection period was from January 2014 to May 2015. Procedures for collecting sociodemographic and clinical data, obtaining analytical parameters and performing office blood pressure and anthropometric measurements have been reported in a prior publication [9]. A food frequency questionnaire (FFQ) validated for Spain [10] was used to calculate composition of carbohydrates, proteins and fats, total calories and GI for each participant’s diet. In the FFQ, subjects indicated the frequency of intake of a number of food items during the previous year, divided into nine categories of consuming, © 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Sanchez-Aguadero et al. Nutrition Journal (2016) 15:88 ranging from never to more than six times per day. The daily dietary GI for each subject was computed dividing his dietary glycemic load (GL) by his total carbohydrate intake per day. Dietary GL was obtained by summing GL of each consumed food (corresponding GI x carbohydrate content per serving x average number of servings per day) [1]. Retinography was performed using a Topcon TRC NW 200 non-mydriatic retinal camera (Topcon Europe B.C., Capelle a/d Ijssel, The Netherlands), obtaining nasal and temporal images centered on the disc. The nasal image with the centered disc was loaded into an arteriolar-venular index (AVI) calculator developed for us (Ciclorisk SL, Salamanca, Spain; registry no. 00/2011/589), whose validation has been published elsewhere [11]. This software automatically recognizes the disc and draws two external concentric circles which delimit area A, between 0 and 0.5 disc diameters from the optic disc margin; and area B, between 0.5 and 1 disc diameters from the margin. It finally estimates the mean caliber of venules and arterioles circulating through area B in micrometers (μm), and summarizes them as a ratio, AVI. An AVI of 1.0 suggests that arteriolar diameters are on average the same as venular diameters in that eye; whereas a smaller AVI suggests narrower arterioles [12]. We used the pairs of main vessels in the upper and lower temporal quadrants, rejecting the rest, to improve the reliability and increase efficiency of the process. Continuous variables were expressed as the mean ± standard deviation, and qualitative variables as frequency distributions. We used a multivariate analysis based on the analysis of covariance (ANCOVA) method, to compare the retinal microvasculature variables between tertiles of GI. The model was adjusted for age, gender, total energy intake, body mass index (BMI), systolic blood pressure (SBP) and medical treatment (antihypertensive, antidiabetic and lipid-lowering drugs). IBM SPSS Statistics for Windows version 23.0 (Armonk, NY: IBM Corp) was used. A value of p < 0.05 was considered statistically significant. Results The mean age of the sample group was 51.6 years (64.3 % females), of whom 77 (25.7 %) were hypertensives, 13 (4.3 %) were type 2 diabetics, 84 (28 %) had dyslipidemia, 73 (24.3 %) had a BMI higher than 30 kg/m2 and 83 (27.7 %) were smokers. The proportion of patients treated with antihypertensive, antidiabetic and lipidlowering agents was 20.7 %, 4.3 % and 14 %, respectively. The mean blood pressure (BP) was 121/74 mmHg, with a mean BMI of 27.3 Kg/m2 and a waist circumference of 92.9 cm. The median values of total cholesterol, triglycerides, serum glucose and HbA1c were 200.5 mg/dl, 99.7 mg/dl, 85.3 mg/dl and 5.4 %, respectively. The Page 2 of 5 average total energy intake was 2547.9 ± 757.0 Kcal/day with a mean carbohydrates consumption of 274.7 ± 97.7 g/day and an overall GI of 47.8 ± 5.5. The mean AV (...truncated)