Abstract
To better understand the sex differences in body mass index (BMI) observed in black South African adults in the Transition and Health during Urbanization of South Africans Study, the present study investigated whether these differences can be explained by the psycho-sociodemographic factors and/or health-related behaviours. A cross-sectional survey was undertaken among 1,842 black South African individuals from 37 study sites that represented five levels of urbanization. The behavioural factors that possibly could have an influence on the outcome of body-weight and that were explored included: diet, smoking, level of education, HIV infection, employment status, level of urbanization, intake of alcohol, physical activity, and neuroticism. The biological factors explored were age and sex. The prevalence of underweight, normal weight, and overweight among men and women was separately determined. The means of the variables were compared by performing Student's t-test for normally-distributed variables and Mann-Whitney U-test for non-normally-distributed variables. The means for the underweight and overweight groups were tested for significant differences upon comparison with normal-weight individuals stratified separately for sex. The differences in prevalence were tested using chi-square tests (p<0.05). All the variables with a large number of missing values were tested for potential bias. The association between sex and underweight or overweight was tested using the Mantel-Haenszel method of odds ratio (OR) and calculation of 95% confidence interval (CI), with statistical significance set at p<0.05 level. Logistic regression was used for controlling for confounders and for testing for effect modification. Females were more likely to be overweight/obese (crude OR=5.1; CI 3.8-6.8). The association was attenuated but remained strong and significant even after controlling for the psycho-sociodemographic confounders. In this survey, the risk for overweight/obesity was strongly related to sex and not to the psycho-sociodemographic external factors investigated. It is, thus, important to understand the molecular roots of sex- and gender-specific variability in distribution of BMI as this is central to the future development of treatment and prevention programmes against overweight/obesity.
Highlights
The nutrition transition describes a pattern of dietary and activity changes often observed in countries experiencing economic growth [1,2]
Results of a study in South Africa on black teenagers showed that girls were more prone to overweight/obesity compared to boys [11]
Surveys in Brazil showed that the prevalence of overweight/ obesity in this country was similar for men and women
Summary
The nutrition transition describes a pattern of dietary and activity changes often observed in countries experiencing economic growth [1,2]. The association of overweight and obesity with women in the African context needs to be explained It is not clear whether sex or gender differences, or both, play a role. As used in recent literature, the concept ‘sex differences’ refers to those variables that are exclusively biological whereas the ‘gender differences’ refer to the socially-defined differences between men and women and by definition include variables relating to possible interactions between the biological and the environmental factors [10]. As this study will focus on the possible role played by the psycho-sociodemographic and behavioural variables (which may include interactions among biological and environmental variables), the concept of ‘gender differences’ is preferred in the discussion rather than ‘sex differences’
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