Covariates

Age, marital status (married versus not), major self-reported doctor diagnosed diseases i.e. heart disease, stroke, cancer, chronic lung disease, and diabetes mellitus, educational attainment (measured using three levels ranging from no qualifications to A-levels or higher), and total net household wealth (divided into tertiles) were considered as potential confounders. Baseline body mass index (<25 kg/m², 25 to <30 kg/m², and ≥30 kg/m²), self-reported smoking (current, former, or never smoker), and physical activity (categorized in four categories ranging from no physical activity to vigorous physical activity at least once a week) were included as covariates. Due to the small number of individuals in the underweight category (i.e. BMI<18.5) (n = 28 women and n = 15 men) we merged this category with the normal weight. Anemia was measured using hemoglobin according to the World Health Organization criteria (WHO): <13g/dL in men and <12g/dL in women [19]. High sensitivity C-reactive protein (hsCRP) and fibrinogen were used as markers of inflammation; hsCRP was log transformed because of its markedly skewed distribution. Marital status, socioeconomic position markers such as education and wealth are major determinants of human health and could well be confounding the observed associations.