Covariates
We also controlled a series of confounders,
including age (years), race (White,
Mixed, Asian or Asian British, Black or Black British, Chinese or Other
ethnic group), education (age at completing continuous full time
education), Townsend Deprivation index (a composite measure of
deprivation based on unemployment, non-car ownership, non-home
ownership, and household overcrowding), smoking statues (never, past and
current), drinking (daily or almost daily, three or four times a week,
once or twice a week, one to three times a month, special occasions only
or never), moderrate activity (Metabolic Equivalent Task (MET) minutes
per week for moderate activity), the body mass index (BMI), histories of
diseases (diabetes, hypertension, asthma, emphysema and chronic
bronchitis), female specific factors (use of oral contraceptive pills,
history of stillbirth, spontaneous miscarriage or termination, menarche,
age at menopause and length of menstrual cycle) in all models. Details
of the assessment of covariates are described in Supplementary material.