Measurements
Baseline and 1-year health assessment included anthropometric (height and weight) and clinical measurements (blood glucose, blood pressure, and lipids) by trained staff following standard operating procedures (17). Standardized self-report questionnaires collected information on sociodemographic characteristics (age, sex, occupation, and ethnicity), alcohol consumption, smoking status, and prescribed medications. Social class was defined according to the Registrar General’s occupation-based classification and comprised the following three categories: “professional, managerial, and technical”; “skilled - manual and nonmanual”; and “partly skilled or unskilled.” Physical activity was assessed by past year total physical activity energy expenditure (net MET hours day-1) using the previously validated European Prospective Investigation into Cancer-Norfolk Physical Activity Questionnaire (22). Dietary behavior was assessed using a validated food- frequency questionnaire (23). Plasma vitamin C level, an objective biomarker of fruit and vegetable consumption, was measured using a fluorometric assay. A plasma vitamin C concentration of > 70 umol L-1 roughly equates to the daily consumption of five servings of fruit and vegetables (24).