Summary
Background
The
contribution of various risk factors to the burden of stroke worldwide
is unknown, particularly in countries of low and middle income. We aimed
to establish the association of known and emerging risk factors with
stroke and its primary subtypes, assess the contribution of these risk
factors to the burden of stroke, and explore the differences between
risk factors for stroke and myocardial infarction.
Methods
We
undertook a standardised case-control study in 22 countries worldwide
between March 1, 2007, and April 23, 2010. Cases were patients with
acute first stroke (within 5 days of symptoms onset and 72 h of hospital
admission). Controls had no history of stroke, and were matched with
cases for age and sex. All participants completed a structured
questionnaire and a physical examination, and most provided blood and
urine samples. We calculated odds ratios (ORs) and
population-attributable risks (PARs) for the association of all stroke,
ischaemic stroke, and intracerebral haemorrhagic stroke with selected
risk factors.
Findings
In the first
3000 cases (n=2337, 78%, with ischaemic stroke; n=663, 22%, with
intracerebral haemorrhagic stroke) and 3000 controls, significant risk
factors for all stroke were: history of hypertension (OR 2·64, 99% CI
2·26–3·08; PAR 34·6%, 99% CI 30·4–39·1); current smoking (2·09,
1·75–2·51; 18·9%, 15·3–23·1); waist-to-hip ratio (1·65, 1·36–1·99 for
highest vs lowest tertile; 26·5%, 18·8–36·0); diet risk score (1·35, 1·11–1·64 for highest vs
lowest tertile; 18·8%, 11·2–29·7); regular physical activity (0·69,
0·53–0·90; 28·5%, 14·5–48·5); diabetes mellitus (1·36, 1·10–1·68; 5·0%,
2·6–9·5); alcohol intake (1·51, 1·18–1·92 for more than 30 drinks per
month or binge drinking; 3·8%, 0·9–14·4); psychosocial stress (1·30,
1·06–1·60; 4·6%, 2·1–9·6) and depression (1·35, 1·10–1·66; 5·2%,
2·7–9·8); cardiac causes (2·38, 1·77–3·20; 6·7%, 4·8–9·1); and ratio of
apolipoproteins B to A1 (1·89, 1·49–2·40 for highest vs lowest
tertile; 24·9%, 15·7–37·1). Collectively, these risk factors accounted
for 88·1% (99% CI 82·3–92·2) of the PAR for all stroke. When an
alternate definition of hypertension was used (history of hypertension
or blood pressure >160/90 mm Hg), the combined PAR was 90·3%
(85·3–93·7) for all stroke. These risk factors were all significant for
ischaemic stroke, whereas hypertension, smoking, waist-to-hip ratio,
diet, and alcohol intake were significant risk factors for intracerebral
haemorrhagic stroke.
Interpretation
Our
findings suggest that ten risk factors are associated with 90% of the
risk of stroke. Targeted interventions that reduce blood pressure and
smoking, and promote physical activity and a healthy diet, could
substantially reduce the burden of stroke.
Funding
Canadian
Institutes of Health Research, Heart and Stroke Foundation of Canada,
Canadian Stroke Network, Pfizer Cardiovascular Award, Merck,
AstraZeneca, and Boehringer Ingelheim.
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