Design and study population
We analysed baseline survey data from the UK Biobank (UKB), a large population-based prospective cohort study that recruited via mail 500 000 adults aged 40–69 years residing within 40 km of 22 assessment centres across England, Scotland and Wales between 2006 and 2010.14 Participation required presenting to the assessment centres and providing written informed consent. Participants who had completed the baseline survey, and reported previously being informed by a health professional that they had hypertension (aware), and reported use of antihypertensive medications (treated) were included in this analysis. We specified exclusion criteria a priori and excluded participants who were pregnant, had fewer than two BP measurements at the baseline visit or had implausible BP values (defined as previously reported15: systolic BP <70 mm Hg or ≥270 mm Hg, diastolic BP <50 mm Hg or ≥150 mm Hg). We additionally excluded participants who had a medical history notable for a condition: associated with poor prognosis (kidney failure, heart failure, liver failure, cancer other than skin); or for which the goals of care might take priority over hypertension control (eg, suicide attempt); or for which the participant may have required additional support from a caretaker for hypertension management, acknowledging that the UKB database did not include measures of severity of these conditions (schizophrenia, dementia, Parkinson’s disease, multiple sclerosis, myasthenia gravis, motor neuron disease, other demyelinating disease).
Procedures and definitions
The UKB baseline information was gathered through (1) a self-administered computer touch screen structured questionnaire at survey centres, followed by (2) same-day in-person structured interview by a trained nurse, which was then followed by (3) physical measurements by a trained nurse (BP, weight, waist circumference). The in-person interview was coupled with review of the participant’s medication list, which participants had been asked to bring with them (over 80% of UKB participants complied). The survey collected information on sociodemographic characteristics, lifestyle health-related behaviour, medical history, family history of CVD and previous health screenings. BP measurement was performed twice, 1 min apart, with the participant in a sitting position and using an Omron HEM 7015-T automated sphygmomanometer. Participants with elevated BP (or other abnormal findings) were provided with a print-out of their results and advised to follow-up with their general practitioner.
Hypertension control was defined as having a mean systolic BP <140 mm Hg and diastolic BP <90 mm Hg, among individuals who reported previously being informed of a hypertension diagnosis by a health professional (aware) as well as use of antihypertensives (treated). The BP treatment target used is consistent with the UK National Institute for Health and Care Excellence (NICE) guidelines for hypertension management during the study period (NICE 2006) and other guidelines such as the United States’ seventh Report of the Joint National Committee on High BP, WHO-International Society of Hypertension and the European Society of Hypertension.16
Reported use of antihypertensives was via either one of two means. First, selection of ‘BP medication’ in response to the touchscreen question ‘Do you regularly take any of the following medications?’ Second, report during the interview of use of medications that are antihypertensives and which were subsequently assessed to be ‘probably for hypertension indication’ based on an antihypertensive treatment rubric we developed. This rubric was based on the NICE 2006 guidelines and employed the Anatomical Therapeutic Chemical classification system,17 which has been endorsed by the WHO and has been similarly applied in a previous UKB publication.18 In applying this rubric, we classified hypertensives as on antihypertensives ‘probably for hypertension indication’ if they were on medications in the first to fourth lines of treatment in 2006 NICE clinical algorithm, but did not report a diagnosis that was an alternate indication for the medications (eg, diabetes for ACE inhibitors).
Variables that were included in the analyses were sociodemographic characteristics, known or possible determinants of CVD (alcohol intake, smoking, physical activity, body mass index (BMI)) or hypertension control (number of comorbidities, types of comorbidities, number of antihypertensive medications, prior colorectal cancer screening as a proxy for healthcare utilisation). BMI was calculated by dividing weight by height squared (kg/m2) and categorised as: underweight <18.5 kg/m2, normal 18.5–24.9 kg/m2, overweight 25.0–29.9 kg/m2 and obese ≥30.0 kg/m2. Standard alcohol units (alcohol by volume equivalents) were derived from participant responses of the number of typical volume drinks for each type of alcohol consumed per week (eg, pint of beer, glass of wine, measure/shot of spirits/liquors). Physical activity was assessed using adapted questions from the validated short International Physical Activity Questionnaire19; the time spent in vigorous, moderate and walking activity was weighted by the energy expended for these categories of activity, to produce total metabolic equivalent task minutes per week. The Townsend deprivation index, based on the geographic unit of census output areas, is a measure of socioeconomic material deprivation that combines four variables routinely available in census data (unemployment, non-ownership of a car, non-ownership of a home and overcrowding at home) and strongly correlates with mortality.20 Education categories followed the scales used in the International Standard Classification of Education, while occupation categories followed the UK Office of National Statistics’ Standard Occupational Classification system.
In selecting comorbidities to be analysed, we took into consideration the prevalence of each condition in the middle-aged population of the UK, its clinical significance, as well as its inclusion in previous multimorbidity studies10 12 21 and the UK’s Quality Outcomes Framework—a pay-for-performance scheme to incentivise quality care by general practitioners. Conditions thus selected spanned cardiometabolic, respiratory, psychiatric and neurological systems. CVD was defined as ischaemic heart disease, stroke or transient ischaemic attack.
Statistical analysis
Descriptive analyses were performed to compute the proportion of hypertension control, overall and stratified. Logistic regression models were fitted to compute unadjusted, age-adjusted and sex-adjusted and multiply-adjusted ORs and 95% CIs of explanatory variables. Sensitivity analysis was performed using only the second BP measurement (which tended to be lower than the first measurement). Exploratory analyses were performed to interrogate potential explanations for the results, the impact of excluding those with serious comorbidities, and effect modification by age group, number of comorbidities and presence of prior CVD. Agreement of BP measurements over time was assessed using Spearman correlation coefficients, for all UKB participants who had repeat BP measured within 3 years of the baseline visit (n 2134, or 0.4% of all UKB participants). All analyses were performed using R V.3.6.2.22