THE MEDIATING EFFECT OF INCOME AND EDUCATION USING THE UK NATIONAL AND DIETARY SURVEY (NDNS) DATA

Diet substantially contributes to socioeconomic inequalities in cardiovascular morbidity and mortality. High adherence to the dietary approach to stop hypertension (DASH) has been proved effective in lowering blood pressure in patients with cardiovascular disease (CVD) as well as to prevent CVD risk factors in the general population. Little is known about time trends in diet quality and associated inequalities in the United Kingdom (UK). In addition, the causal pathway between education and dietary choices has not been fully explained and the role of income in preventing a healthy diet has not been clarified. This doctorate firstly, aimed to quantify the differences in adherence to the DASH in relation to socioeconomic position (SEP) in the UK and to evaluate recent trends. Secondly, it aimed to quantify the mediating effect of income on the relationship between education and the DASH score in the UK population. Data used for analysis was obtained from three waves of the National Diet and Nutrition Survey Rolling Programme (NDNS) 2008-2012, 2013-2014 and 2015-2016). The DASH score was calculated based on Fung et al methodology and was calculated using sex-specific quintiles of DASH items. For the first part of the analysis (Paper 2) data analysis included 6435 subjects aged 18 and older who participated in the NDNS. Multiple linear regressions were used to evaluate the relationship between the socioeconomic variables and the DASH score. Quantile regression analysis was used to model the median intake of each component as a function of the socioeconomic variable and the survey year. In the second analysis (Paper 3), analysis was done on 4864 subjects aged 18 and older. Counterfactual-based mediation analysis was carried out to decompose the total effect of education on DASH score into average direct effect (ADE) and average causal mediation effect (ACME) mediated by income. A gradient relationship between the DASH score and all socioeconomic variables emerged with increasing values of the score at higher socioeconomic positions (SEP effect p value: <0.0001 for education, occupation, and income) in the initial analysis. The interaction term between survey year and the socioeconomic variables was not significant showing that the trend was not different across socioeconomic groups (p >0.05). The estimated difference between people with no qualification and those having the highest level of education was -3.59 points (95% CI: -3.91; -3.20). The difference between people engaged in routine occupations and those engaged in high managerial and professional occupations was -3.40 points (95% CI: -3.87; -2.92), and the difference between subjects in the first fifth and last fifth of the household income distribution was -2.73 points (95% CI: -3.16; -2.29). The widest socioeconomic differences emerged for consumption of fruit, vegetables, whole grains, nuts, seeds and legumes. Mediation analysis indicated that the overall mediating effect of income on the relationship between education and the DASH score was only partial, with an estimated proportion mediated ranging between 6 to 9%. The mediating effect was higher among women (11.6%) and younger people (17.9%). Findings from this doctorate add an important contribution to the existing literature and more importantly, provide an updated picture of socio-economic inequalities in diet amongst UK adults in context of the whole diet. The results show that overall, the DASH score increased over time, yet the overall score remains low. Moreover, persistent disparities between individuals with higher versus lower SEP were observed. Additional analysis indicates that low income plays a modest role in explaining educational differences in the UK population. Further research is needed to investigate which other factors may explain differences in diet quality. In conclusion, findings in this doctorate have substantial implications for public nutrition policy. An immediate implication is the need for public nutrition policies that are individualised to SEP. Targeted interventions for those within the lower SEP need a multi-factorial approach not just focusing on the cost of food but on other factors such as nutrition literacy, attitudes towards healthy eating as well as access to healthy food. Further research is needed to fully investigate which other factors may explain the socioeconomic inequality in the adoption of the DASH diet in UK. THE THESIS IS BASED ON THE FOLLOWING PUBLISHED PAPERS 1. Patel,L.Alicandro,G,LaVecchia,C(2018).Low-CalorieBeverageConsumption, Diet Quality and Cardiometabolic Risk Factors in British Adults. Nutrients, 10 2. Patel L, Alicandro G, La Vecchia C (2020) Dietary approach to stop hypertension (DASH) diet and associated socioeconomic inequalities in the United Kingdom. Br J Nutr, 1-24. – AWARDED UK NUTRITION SOCIETY PAPER OF THE MONTH JUNE 2020. 3. Patel L, Bertuccio P, Alicandro G, La Vecchia C (2020). Educational inequality in the dietary approach to stop hypertension (DASH) diet in the UK: evaluating the mediating role of income. Br J Nutr, 1-20