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Dominant modifiable risk factors for stroke in Ghana and Nigeria (SIREN): a case-control study


We have identified the top 11 modifiable risk factors that account for 98·2% of PAR associated with stroke among people from Ghana and Nigeria in the largest study done on stroke in Africa. Our findings build on those of INTERSTROKE,9x9O’Donnell, MJ, Chin, SL, Rangarajan, S et al. Global and regional effects of potentially modifiable risk factors associated with acute stroke in 32 countries (INTERSTROKE): a case-control study. Lancet. 2016; 388: 761–775
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Furthermore, to increase the applicability of our findings in routine clinical settings, we analysed intake of various dietary components individually, not as a composite dietary score,9x9O’Donnell, MJ, Chin, SL, Rangarajan, S et al. Global and regional effects of potentially modifiable risk factors associated with acute stroke in 32 countries (INTERSTROKE): a case-control study. Lancet. 2016; 388: 761–775
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Dietary and socioeconomic factors seem to play more important roles in predisposition to stroke among Africans than previously appreciated. Regular intake of meat, added table salt, and low consumption of green leafy vegetables were associated with stroke in both countries in the present study. Higher income was independently associated with stroke (significantly in the US$101–250 band) and was also associated with increased salt and meat intake, but decreased vegetable intake in cases, suggesting that poor dietary choices might be underpinned by higher income level (appendix). Although the effect of high salt intake might be mediated via hypertension occurrence or control, red meat is a source of saturated fatty acids and cholesterol, and has been associated with increased risk of stroke in a dose-dependent manner elsewhere.27x27Yang, C, Pan, L, Sun, C, Xi, Y, Wang, L, and Li, D. Red meat consumption and the risk of stroke: a dose-response meta-analysis of prospective cohort studies. J Stroke Cerebrovasc Dis. 2016; 25: 1177–1186
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We found consistent associations between stress and occurrence of ischaemic and haemorrhagic strokes. An almost doubled risk of fatal stroke has been reported among participants with self-reported high stress intensity compared with those without stress.30x30Truelsen, T, Nielsen, N, Boysen, G, and Grønbæk, M. Self-reported stress and risk of stroke the Copenhagen City Heart Study. Stroke. 2003; 34: 856–862
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Pathophysiologically, ischaemic strokes were commonly of lacunar subtype followed by large-artery atherosclerosis and cardioembolic strokes. 87% of haemorrhagic strokes were attributed to hypertension on the basis of the SMASH-U classification,17x17Meretoja, A, Strbian, D, Putaala, J et al. SMASH-U: a proposal for etiologic classification of intracerebral hemorrhage. Stroke. 2012; 43: 2592–2597
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The mean age of the study population was 59 years, which shows the heavy economic toll stroke exerts in sub-Saharan Africa by affecting a relatively young and productive population. Although there were differences in effect sizes, the spectrum of risk factors associated with stroke occurrence among young Africans (age <50 years) were similar to those among the older population. The emergence of traditional vascular risk factors as dominant predispositions for stroke occurrence in those younger than 50 years is an indication of a rapid emergence of cardiovascular risk factors at early ages in sub-Saharan Africa. An implication is that public health interventions aimed at remediation of the traditional risk factors and the novel dietary and psychosocial factors identified are likely to lead to a reduction in stroke burden across the different age strata among the adult population.

Case-control studies such as ours cannot establish causality, but rather seek to show associations and quantify effect sizes of risk factors. Furthermore, we adopted measures similar to INTERSTROKE9x9O’Donnell, MJ, Chin, SL, Rangarajan, S et al. Global and regional effects of potentially modifiable risk factors associated with acute stroke in 32 countries (INTERSTROKE): a case-control study. Lancet. 2016; 388: 761–775
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A substantial number of patients with stroke in our study had severe strokes at the time of recruitment, necessitating a proxy investigation of lifestyle and behavioural history (appendix). Valid proxies were spouses or first-degree relatives who had lived with the patient within the year before the stroke. The associations observed among proxies were in the same direction as for patients with direct assessment. Because of the high proportion of critically ill patients with stroke, not all patients could undergo exhaustive investigations to establish the cause of ischaemic and haemorrhagic strokes before their death. Nevertheless, we have provided comprehensive data on the burden of causative subtypes of stroke among Africans, to our knowledge, for the first time.

An important strength of our study was an active community engagement arm throughout the study duration to minimise presentation bias for cases and controls thereby enhancing representativeness to promote generalisability (appendix). 83% of our controls were community based and recruited from the catchment population of the cases, thereby fulfilling the ideal recommendation of community-based controls.18x18O’Donnell, M, Xavier, D, Diener, C et al. Rationale and design of INTERSTROKE: a global case-control study of risk factors for stroke. Neuroepidemiology. 2010; 35: 36–44
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Indeed, the risk factors identified in the SIREN study provide context-specific potential targets for public health control of stroke on the African continent and potentially in other low-income and middle-income countries. First, given the effect of hypertension on stroke occurrence globally and among Africans in particular, the need for enhanced awareness, detection, and control of this risk factor for stroke is urgent. Second, clusters of other metabolic risk factors such as dyslipidaemia, diabetes, and obesity have become important targets for multi-pronged interventions for stroke prevention. Third, health promotion campaigns geared towards healthy dietary choices and exercise are likely to help curb the rising burden of stroke among Africans.



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