Differences in Risk Factors Between Black Caribbean Patients With Stroke in Barbados and South London
Background and Purpose— Risk of stroke is higher in black Caribbeans in the United Kingdom compared with black Caribbeans in their country of origin. We investigated if these differences were caused by variations in prior-to-stroke risk factors.
Summary of Report— Data were collected from the South London Stroke Register (SLSR) and the Barbados Register of Strokes (BROS). Differences in prevalence and management of stroke risk factors were adjusted for age, sex, living conditions prestroke, stroke subtype, and socioeconomic status by multivariable logistic regression. Patients in BROS were on average older (mean difference 4 years) and more likely to have a nonmanual occupation. They were less likely to have a prestroke diagnosis of myocardial infarction (OR, 0.39; 95% CI, 0.19 to 0.77) or diabetes (OR, 0.65; 95% CI, 0.46 to 0.92) and were less likely to report smoking (OR, 0.31; 95% CI, 0.19 to 0.49). They were also more likely to receive appropriate prestroke antihypertensive (OR, 1.88; 95% CI, 1.21 to 2.92) and antidiabetic treatment (OR, 3.33; 95% CI, 1.44 to 7.70) and less likely to receive cholesterol-lowering drugs (OR, 0.19; 95% CI, 0.05 to 0.71).
Conclusions— The higher risk of stroke in black Caribbeans in the United Kingdom might be caused by a higher prevalence of major prior-to-stroke risk factors, differences in treatment patterns for comorbid conditions, and less healthy lifestyle practices compared with indigenous black Caribbean populations.
A previous comparison of stroke incidence in black Caribbeans (BC) between Barbados and South London showed that BC in the United Kingdom had an age-standardized incidence of total stroke of approximately 25% greater compared with BC in their region of origin.1 These findings could be due to differences in the prevalence of the main risk factors for stroke. We therefore compared risk factors and their treatment in BC in South London and Barbados adjusting for differences in demographic and socioeconomic characteristics.
The South London Stroke Register (SLSR), a population-based stroke register recording all first-ever strokes in patients of all age groups for a defined area of South London, was set up in January 1995.2 The source population of the SLSR are the 271 817 residents (UK Census 2001) of whom 63% were white, 9% BC, 15% black African, 4% black Mixed, 5% Asian, and 4% other. The population-based Barbados Register of Strokes (BROS) was set up in October 2001.3 The BROS cases came from a population of 268 762 (Barbados Census 2000) comprising 93% BC, 3% black mixed, 3% white, and 1% other. Both SLSR and BROS record hospitalized and nonhospitalized cases.
The SLSR and BROS used identical data collection methods and standardized variable definitions. For both registers, overlapping sources of patient notification were used to ensure completeness of case ascertainment; details have been published elsewhere.4
Stroke was defined by the World Health Organization categories3 and classified according to the underlying pathology into cerebral infarction, primary intracerebral hemorrhage, and subarachnoid hemorrhage.
Ethnic group was self-defined by the patients or their relatives. Socioeconomic status was recorded for the SLSR using the UK Registrar General’s codes based on occupation5 and for BROS the national census questions3 and was grouped into nonmanual, manual, and unknown according to the patient’s current (or for the retired and others not currently working, the most recent) employment. Living circumstances prestroke were grouped into fully independent (private household alone), some independence (private household with others, sheltered home), nursing or hospital care. Data were collected from their general practice or hospital records on hypertension (greater than 140 mm Hg systolic or greater than 90 mm Hg diastolic), myocardial infarction (MI), atrial fibrillation, hypercholesterolemia, transient ischemic attack, and diabetes mellitus. Prestroke smoking was recorded as current, exsmoker, or nonsmoker and reported high alcohol intake as ≥14 U per week for women and ≥21 U per week for men. Using medical records, prescription of the following medications prior to stroke was recorded: antihypertensives, hypoglycemic drugs/insulin, antiplatelets, warfarin, and cholesterol-lowering drugs. Antihypertensives were considered appropriate for patients with known hypertension prestroke, oral hypoglycemic drugs/insulin for those with a history of diabetes mellitus prior to stroke, antiplatelets for those with MI and/or transient ischemic attack prior to stroke, warfarin for those with atrial fibrillation, and cholesterol-lowering drugs for those with hypercholesterolemia.
Analyses were restricted to BC. The observed differences between BROS and SLSR in prevalence of prior-to-stroke risk factors and their management were adjusted for sex, age (continuous), stroke subtype, social class, and living circumstances by multiple logistic regression.
Patients and/or their relatives gave written informed consent to participate in the study. The design of the study was approved for SLSR by the ethics committees of Guy’s and St Thomas’ Hospital Trust, Kings College Hospital, Queens Square, Westminster Hospital (London) and for BROS from the Medical Research Ethics Committee of the Ministry of Health (Barbados).
Between January 1995 and December 2004, 336 BC patients with a first in a lifetime stroke were registered in the SLSR. Between October 2001 and March 2005, BROS registered 989 BC patients.
Sociodemographic factors and clinical severity characteristics for patients in SLSR and BROS are compared in Table 1. BROS stroke patients were older, a higher proportion were women, they were more likely to have a nonmanual occupation, and were less likely to be independently functioning prestroke. Table 2 compares stroke risk factors and comorbid conditions. Hypertension prevalence was slightly higher in SLSR patients, whereas there was a 2-fold higher frequency of prestroke MI.
After adjustment, patients in Barbados were less likely to have had a prior-to-stroke diagnosis of MI and diabetes and less likely to have been smokers and were more likely to have received prestroke antihypertensive treatment, oral hypoglycemics, and/or insulin and less likely to have received cholesterol-lowering drugs (Table 3).
This is the first study comparing risk of stroke and its association with prevalence and management of vascular risk factors between migrant populations and similar populations in their countries of origin. In general, there was a more favorable risk factor profile for BC stroke patients living in Barbados compared with BC in the United Kingdom, which could explain the lower risk of stroke among BC in the Caribbean. In addition, patients in Barbados were more likely to have received appropriate prior-to-stroke management of vascular risk factors with the exception of lipid-lowering drugs compared with South London. Because better management of prior-to-stroke risk factors might be linked with a decrease in stroke incidence,6 these differences might contribute to the lower stroke incidence in BROS.
Some of the variations of major vascular risk factors might be caused by differences in environmental conditions. For example, the lower prevalence of MI in Barbados might be caused by lower saturated fat intake in the Caribbean islands compared with the United Kingdom.7 Because lower socioeconomic status is associated with a high prevalence of vascular risk factors8 and immigrants usually have a lower socioeconomic status when coming to a new country,9 differences in socioeconomic status of patients with stroke between Barbados and South London might also explain some of the variation, although we have adjusted for social class. The better management of prior-to-stroke risk factors in BC in Barbados compared with South London might reflect ethnic variations in access to health care between migrant and indigenous populations.10
There are limitations to this study. These analyses are retrospective because data were derived from stroke registers. However, currently there are no data from cohort studies available on risk factors for stroke in the Caribbean. The study periods for SLSR and BROS are not completely matched. However, in sensitivity analysis restricted to identical time periods, similar point estimates are observed. The BC populations might not be directly comparable; only a minority of SLSR Caribbeans originate from Barbados with most having Jamaica as their country of origin.11
We thank all the patients and their families and the health care professionals involved. Particular thanks go to all the fieldworkers involved with SLSR and BROS.
Sources of Funding
This study was supported by the (South London) Northern & Yorkshire NHS R&D Programme in Cardiovascular Disease and Stroke, Charitable Foundation of Guy’s and St Thomas’ Hospitals, Stanley Thomas Johnson Foundation, Department of Health, UK through the National Institute for Health Research (NIHR) Biomedical Research Centre award to Guy’s & St Thomas’ NHS Foundation Trust in partnership with King’s College London; (Barbados) Wellcome Trust and the Ministry of Health, Barbados.
- Received March 4, 2008.
- Revision received May 8, 2008.
- Accepted May 27, 2008.
Wolfe CDA, Corbin DOC, Smeeton NC, Gay GHE, Rudd AG, Hennis AJ, Wilks RJ, Fraser HS. Estimation of the risk of stroke in black populations in Barbados and South London. Stroke. 2006; 37: 1986–1990.
Stewart JA, Dundas R, Howard RS, Rudd AG, Wolfe CDA. Ethnic differences in incidence of stroke: prospective study with stroke register. BMJ. 1999; 318: 967–971.
Corbin DO, Poddar V, Hennis A, Gaskin A, Rambarat C, Wilks R, Wolfe CDA, Fraser HS. Incidence and case fatality rates of first-ever stroke in a black Caribbean population: the Barbados Register of Strokes. Stroke. 2004; 35: 1254–1258.
Tilling K, Sterne JA, Wolfe CD. Estimation of the incidence of stroke using a capture–recapture model including covariates. Int J Epidemiol. 2001; 30: 1351–1359.
Wolfe CD, Rudd AG, Howard R, Coshall C, Stewart J, Lawrence E, Hajat C, Hillen T. Incidence and case fatality rates of stroke subtypes in a multiethnic population: the South London Stroke Register. J Neurol Neurosurg Psychiatry. 2002; 72: 211–216.
Rothwell PM, Coull AJ, Giles MF, Howard SC, Silver LE, Bull LM, Gutnikov SA, Edwards P, Mant D, Sackley CM, Farmer A, Sandercock PAG, Dennis MS, Warlow CP, Bamford JM, Anslow P. Change in stroke incidence, mortality, case-fatality, severity, and risk factors in Oxfordshire, UK from 1981 to 2004 (Oxford Vascular Study). Lancet. 2004; 363: 1925–1933.
Mennen LI, Jackson M, Sharma S, Mbanya J-CN, Cade J, Walker S, Riste L, Wilks R, Forrester T, Balkau B, Cruickshank K. Habitual diet in four populations of African origin: a descriptive paper on nutrient intakes in rural and urban Cameroon, Jamaica and Caribbean migrants in Britain. Public Health Nutrition. 2001; 4: 765–772.
Bhopal R, Hayes L, White M, Unwin N, Harland J, Ayis S, Alberti G. Ethnic and socio-economic inequalities in coronary heart disease, diabetes and risk factors in Europeans and South Asians. J Public Health Med. 2002; 24: 95–105.
Bourke J, Sylvester R, Sharma P. Ethnic variations in the management of patients with acute stroke. Postgrad Med J. 2006; 82: 13–15.