Demographic, socio-economic and behavioural correlates of BMI in middle-aged black men and women from urban Johannesburg, South Africa

ABSTRACT

Background: There is a high and increasing prevalence of overweight and obesity in South Africans of all ages. Risk factors associated with overweight and obesity must be identified to provide targets for intervention.

Objective: To identify the demographic, socio-economic and behavioural factors associated with body mass index (BMI) in middle-aged black South African men and women.

Methods: Data on demographic and socio-economic factors were collected via questionnaire on 1027 men and 1008 women from Soweto Johannesburg, South Africa. Weight and height were measured and BMI was determined. Behavioural factors included tobacco use and consumption of alcohol, and physical activity data were collected using the Global Physical Activity Questionnaire. Menopausal status was determined for the women, and HIV status was available for 93.6% of the men and 39.9% of the women.

Results: Significantly more women were overweight or obese than men (87.9 vs. 44.9%). Smoking prevalence (current or former) and minutes spent in moderate to vigorous intensity physical activity was significantly different between the sexes (both p < 0.0001). In the final hierarchical model, marital status (+ married/cohabiting), household asset score (+), current smoking (-), moderate to vigorous physical activity (-) and HIV status (- HIV infected) significantly contributed to 26% of the variance in BMI in the men. In the women, home language (Tswana-speaking compared to Zulu-speaking), marital status (+ unmarried/cohabiting), education (-), current smoking (-) and HIV status (- HIV infected) significantly contributed to 14% of the variance in BMI.

Conclusions: The sex difference in BMI and the prevalence of overweight and obesity between black South African men and women from Soweto, as well as the sex-specific associations with various demographic, socio-economic and behavioural factors, highlight the need for more tailored interventions to slow down the obesity epidemic.

SPECIAL ISSUE:

• BMI distribution across African communities

KEYWORDS:

• Obesity
• overweight
• physical activity
• socio-economic status
• BMI
• South Africa

Responsible Editor Nawi Ng, Umeå University, Sweden

Responsible Editor Nawi Ng, Umeå University, Sweden

Acknowledgments

This study would not have been possible without the generosity of the participants who spent many hours responding to questionnaires, being measured and having samples taken. We wish to acknowledge the sterling contributions of our fieldworkers, phlebotomists, laboratory scientists, administrators, data personnel and other investigators who contributed to the data and sample collections, processing, storage and shipping. Investigators responsible for the conception and design of the AWI-Gen study include the following: Michèle Ramsay (PI, Wits), Osman Sankoh (co-PI, INDEPTH), Stephen Tollman and Kathleen Kahn (Agincourt PI), Marianne Alberts (Dikgale PI), Catherine Kyobutungi (Nairobi PI), Halidou Tinto (Nanoro PI), Abraham Oduro (Navrongo PI), Shane Norris (Soweto PI), and Scott Hazelhurst, Nigel Crowther, Himla Soodyall and Zane Lombard (Wits). We would like to acknowledge each of the following investigators for their significant contributions to this research, mentioned according to affiliation: Wits AWI-Gen Collaborative Centre – Stuart Ali, Ananyo Choudhury, Scott Hazelhurst, Freedom Mukomana, Cassandra Soo; Soweto (DPHRU): Nomses Baloyi, Yusuf Guman.

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethics and consent

All participants provided written informed consent before any study procedures were conducted. The Human Research Ethics Committee (Medical) of the University of the Witwatersrand approved the protocol (certificate M121029).

Paper context

It is well accepted that obesity is an increasing problem in South Africa, particularly in black women. This paper provides data on the demographic, socio-economic, behavioural and clinical factors associated with body mass index in men and women, and contributes to our understanding of how these factors may differ between the sexes. Significantly more of the variance in BMI can be explained by these factors in the men, and these can represent targets for future interventions which may need to be sex-specific.

Additional information

Funding

The AWI-Gen Collaborative Centre is funded by the National Human Genome Research Institute (NHGRI), the National Institute of Environmental Health Sciences (NIEHS), the Office of AIDS research (OAR) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), of the National Institutes of Health (NIH) under award number U54HG006938, as part of the H3Africa Consortium, by the Department of Science and Technology, Republic of South Africa, award number DST/CON 0056/2014, and by the African Partnership for Chronic Disease Research (APCDR). MR is a South African Research Chair in Genomics and Bioinformatics of African populations hosted by the University of the Witwatersrand, funded by the Department of Science and Technology and administered by National Research Foundation of South Africa (NRF). The Birth to Twenty Cohort (Soweto, South Africa) is supported by University of the Witwatersrand, the Medical Research Council, South Africa, and the Wellcome Trust, UK. SAN is supported by the DST/NRF Centre of Excellence in Human Development at the University of the Witwatersrand, Johannesburg. This paper describes the views of the authors and does not necessarily represent the official views of the National Institutes of Health or the National Research Foundation of South Africa who funded this research.

Notes on contributors

Lisa K. Micklesfield

MR, NC and SN contributed to the conception and design of the study. RM and JK analysed the data. LM interpreted the data and drafted the manuscript. All authors critically reviewed the manuscript, and read and approved the final draft.