Effect of rural-to-urban within-country migration on cardiovascular risk factors in low- and middle-income countries: A systematic review

Context: Limited information is available of effects of rural-to-urban within-country migration on cardiovascular (CV) risk factors in low- and middle- income countries (LMIC). Objective: A systematic review of studies evaluating these effects was performed with rural and/or urban control groups. Study selection: Two teams of investigators searched observational studies in Medline, Web of Science and Scopus until May 2011. Studies evaluating international migration were excluded. Data extraction: Three investigators extracted the information stratified by gender. Information on 17 known CV risk factors was obtained. Results: Eighteen studies (n=58 536) were included. Studies were highly heterogeneous with respect to study design, migrant sampling frame, migrant urban exposure and reported CV risk factors. In migrants, commonly reported CV risk factors - systolic and diastolic blood pressure, body mass index, obesity, total cholesterol and low-density lipoprotein - were usually higher or more common than in the rural group and usually lower or less common than in the urban group. This gradient was usually present in both genders. Anthropometric (waist-to-hip ratio, hip/waist circumference, triceps skinfolds) and metabolic (fasting glucose/insulin, insulin resistance) risk factors usually followed the same gradient, but conclusions were weak as information was insufficient. Hypertension, high-density lipoprotein, fibrinogen and C-reactive protein did not follow any pattern. Conclusions: In LMIC, most but not all, CV risk factors are higher or more common in migrants than in rural groups but lower or less common than in urban groups. Such gradients may or may not be associated with differential CV events and long-term evaluations are necessary.