The Potential Role of Dietary Antioxidant Capacity on Age-Related Macular Degeneration

While being benefited from the results of previous studies, the sample size of the research was type 1 error performance α=0.05 and type 2 error performance β=0.20. The power of the test was taken as 1-β=0.80 and the power analysis was statistically made with NCCS PAS 11 program. 200 individuals voluntarily participated into the study as control group, including 100 patients diagnosed with AMD (50 women, 50 men) and 100 patients not diagnosed as AMD (50 women, 50 men).

Sociodemographic Variables The questionnaire form, prepared to determine socio-demographic features of individuals participating in the research, was applied by the research with the method of face-to-face interview. The socio-demographic features of individuals (gender, age, occupation, educational status, health conditions), use of cigarettes and drugs was questioned.

Anthropometric Variables The body weight of the individuals were measured with a calibrated electronic scale, which could measure even 0.1 kg, while the individuals were hungry, in light clothes and their shoes were taken off. The body lengths were measured by the researcher with the tape measure while they were standing upright in Frankfurt plane position (ear canal and lower margin of orbit in the same horizontal plane, facing forward). BMI was calculated with the formula [body weight (kg)/body length (m2)]. BMI evaluation was made while the classification developed by World Health Organization (WHO) was taken as a basis (13). According to this classification; (BMI<18.5 kg/m2 thin, 18.5< 24.9 kg/m2 normal, 25.0-29.9 kg/m2 overweight and ≥30 kg/m2 obese. The waist circumference of the individuals was measured with tape measure by founding the midpoint between the lowest rib and umbilicus. The relation between waist circumference and chronic diseases is as follows: If the waist circumference is ≥88 cm for women and ≥102 cm for men, it is shown as high risk. The hip circumference of the individuals was measured with a tape measure from the highest point by standing the left side of the individuals. If the waist/hip rate is over 0.85 for women and over 0.90 for men, the risk of chronic diseases increases.

Assesment of dietary intake and diet total antioxidant capacity Participants' dietary intake was assessed using food frequency questionnaire (FFQ). The FFQ included 65 food items traditionally consumed in Turkey. Foods were classified into the following food categories: milk and dairy products, meat and meat products, fruits, vegetables, breads and cereals, beverages, and desserts. Intake frequencies for the food items consisted of eight categories ranging from never/once a month to more than one per day. Trained interviewers asked participants how often they had consumed one portion of each food item in generally. To compute the total amount of food intake per day, the reported frequency of consumption for each food item was multiplied by the portion size and then total food intake was converted to nutrient intake based on the food's nutrient profile. Standardized food recipes for Turkey and Nutrition Information System (BEBIS) program which is a food composition database for nutrient estimation were used to determine average daily energy and nutrient intake for each participant. These values were compared with the recommended daily allowance values to determine the energy and nutrient requirement meeting status and the requirement meeting percentages were calculated.

By using food intake frequency amounts, dietary total antioxidant capacity was tried to be determined approximately with the use of data obtained from a large-scale study made by Carlsen for developing a database including total antioxidant component of essential nutrients. The antioxidant amount in 100 g food given for each nutrient group in the related resource was used as standard antioxidant activity value in this study and the approximate antioxidant activity values of the grouped food intake amounts of individuals were calculated.

Statistical Analysis In the statistical evaluation of data obtained from the study, Statistical Package for Social Science (SPSS) 22.0 program was used. For the data obtained from the measures of individuals participating in the study, average, standard deviation and the lowest and the highest values were calculated. The distribution of data determined with numbers was given with number-percentage tables. While evaluating constant data, it was determined with Kolmogorov Smirnov test whether there was normal distribution or not. The data of individuals having normal distribution were analyzed with parametric statistical tests and the data of individuals not having normal distribution were analyzed with non-parametric statistical tests. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by univariate logistic regression analysis separately for food group, BMI, and adjusted age, gender before combined in multivariate logistic regression. Logistic regression analysis was performed to determine risk factors for AMD using odds ratio estimates with 95% confidence intervals. Furthermore, a stepwise multivariate regression analysis was performed, with p value less than 0.05 being required for entering the model and remaining there.