The European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk cohort study is a prospective population study of 25 639 men and women aged 45–79 years old and living in Norfolk, UK, as described previously. Briefly, EPIC-Norfolk is part of the 10-country collaborative EPIC study designed to investigate determinants of cancer. From the onset, additional data were obtained in EPIC-Norfolk to enable the assessment of determinants of other diseases such as CHD. Participants were enrolled between 1993 and 1997. They completed a detailed health and lifestyle questionnaire and attended a clinic visit where additional data collection was performed by trained nurses. The study cohort was similar to UK population samples with regard to many characteristics, including anthropometry, blood pressure, and lipids, but with a lower proportion of smokers. Baseline prevalence of diabetes mellitus was ascertained by means of self-report of diabetes, diabetic diet, diabetes-specific medication, or diabetes-specific medication brought to the clinical visit. Baseline cardiovascular disease was defined by self-reported myocardial infarction or stroke. The Norwich District Health Authority Ethics Committee approved the study, and all participants gave signed informed consent.
For the current analysis, we applied the JUPITER inclusion and exclusion criteria as accurately as possible with the data available in EPIC-Norfolk (Figure 1). Men 50 years of age or older and women 60 years of age or older were eligible for the analysis if they did not have a history of cardiovascular disease and if, at the initial screening visit, triglyceride levels were <5.6 mmol/L. Study participants for whom LDL-C or C-reactive protein levels were not available, were excluded.
EPIC-Norfolk study participants meeting the JUPITER inclusion criteria. Flow chart displaying the inclusion and exclusion criteria in sequential order of application to EPIC-Norfolk study participants. The group meeting the C-reactive protein and low-density lipoprotein cholesterol criteria of the JUPITER trial has been labeled 'JUPITER eligible.' CVD, cardiovascular disease.
Additional exclusion criteria were previous or current use of lipid-lowering therapy, current use of post-menopausal hormone-replacement therapy, diabetes mellitus, uncontrolled hypertension (systolic blood pressure >190 mmHg or diastolic blood pressure >100 mmHg), uncontrolled hypothyroidism as evidenced by a thyroid-stimulating hormone (TSH) level >7.5 U/L. Because TSH levels were available in approximately half the cohort, this latter exclusion criterion was applied only in individuals for whom TSH was available. Baseline characteristics did not differ significantly between those for whom TSH was or was not available. Since sufficient baseline information was not available on all JUPITER criteria, we did not apply the following exclusion criteria: hepatic dysfunction, a creatine kinase level more than three times the upper limit of the normal range, a creatinine level that was >2.0 mg/dL (176.8 μmol/L), cancer within 5 years before enrolment, and a recent history of alcohol or drug abuse. Patients using immunosuppressant agents or long-term oral glucocorticoids were not excluded because this information was not readily available.
Non-fasting blood samples were drawn into plain and citrate bottles. Blood samples were processed directly at the Department of Clinical Biochemistry, University of Cambridge, or stored at −80°C. Serum levels of total cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides were measured in fresh samples with the RA 1000 (Bayer Diagnostics, Basingstoke, UK). Low-density lipoprotein cholesterol-C levels were calculated using the Friedewald formula. When additional funding became available in 2010, serum concentrations of C-reactive protein were measured in all participants with available frozen baseline serum samples using a full-range, high-sensitivity assay on an Olympus AU640 clinical chemistry analyzer (Olympus UK Ltd, Watford, UK).
All individuals have been flagged for mortality at the UK Office of National Statistics, with vital status ascertained for the entire cohort. Death certificates were coded by trained nosologists according to the International Classification of Diseases 10th revision (ICD-10). In addition, hospitalized participants were identified by using their unique National Health Service number through data linkage with the East Norfolk Health Authority (ENCORE) database, which identifies all hospital contacts throughout England and Wales for residents of Norfolk. Participants were identified as having developed CHD during the follow-up if they had a hospital admission and/or died with CHD as the underlying cause during the follow-up. Coronary heart disease was defined as ICD-10 codes I20–I25 (including acute and old myocardial infarction, angina, and other ischaemic heart disease). We report results with follow-up to 31 March 2008.
The population fulfilling all inclusion criteria was classified into four groups using the LDL-C cut-off value 3.4 mmol/L and the C-reactive protein cut-off value 2 mg/L. Baseline characteristics are presented as mean ± SD for continuous variables with normal distribution, median, and inter-quartile range for continuous variables with non-normal distribution, or percentage (number) for categorical variables. Baseline characteristics were compared between the groups with high vs. low C-reactive protein using a two-sided Student's t-test for continuous variables. C-reactive protein and triglycerides had a skewed distribution and were log-transformed before analysis. Differences in dichotomous variables between groups were analysed by χ test. The Framingham risk score (FRS) was calculated using a previously reported algorithm, which takes into account age, sex, total cholesterol, HDL-C, systolic and diastolic blood pressure, smoking, and the presence of diabetes mellitus. Cox proportional hazard models were used to calculate hazard ratios (HRs) and corresponding 95% confidence intervals (95% CI) for the risk of future CHD. Models were adjusted for age, sex, smoking, systolic blood pressure, HDL cholesterol, and body mass index. Categories were based on quartiles. The lowest category was used as a reference category. Kaplan–Meier curves for CHD-free survival were computed for participants classified into the four groups. Differences between curves were assessed by the log-rank test. Statistical analyses were performed using the SPSS software (version 17; SPSS, Inc., Chicago, IL, USA). A P-value of <0.05 was considered to be statistically significant.