Did socioeconomic inequalities in overweight and obesity in South African women of childbearing age improve between 1998 and 2016? A decomposition analysis.

Researchers: Mweete D.Nglazi and John E. Ataguba.

November 2024

What Is The Study About?

This study assesses the changing patterns in socioeconomic inequality in overweight and obesity among South African non-pregnant WCBA between 1998 and 2016. It uses data from the 1998 and 2016 Demographic and Health Surveys. Socioeconomic inequality in overweight and obesity was assessed using the concentration index. The index was decomposed to identify contributing factors to obesity and overweight inequalities. Factors contributing to changes in inequalities between 1998 and 2016 were assessed using the Oaxaca-type decomposition approach.

Why Is This Important?

Overweight and obesity in adult women contribute to deaths and disability from non-communicable diseases (NCDs) and obesity-related health problems in their offspring. Globally, overweight and obesity prevalence among women of childbearing age (WCBA) has increased, but associated socioeconomic inequality remains unclear.

What We Know…

In South Africa, overweight and obesity prevalence has also increased over time, disproportionately affecting women, especially women of childbearing age (WCBA). The burden of overweight and obesity concerns WCBA (i.e., 15 to 49 years old) because it affects their health and can potentially affect the next generation’s health. Obesity during a woman’s childbearing years is associated with an increased risk of infertility, miscarriage, giving birth to stillbirth children and those with congenital disabilities, shoulder dystocia and other adverse obstetric outcomes. WCBA tend to accumulate weight faster during this life stage.

There are several reasons for the overweight and obesity epidemic occurring during this life stage, with many related to socioeconomic conditions. For example, there are differences between people from wealthier and deprived households in behaviours such as the various types of consumption (smoking, alcohol, processed foods and foods high in fat, salt and sugar) and leisure-time physical activity. Differences in the prevalence of overweight and obesity between socioeconomic groups are partly due to a clustering of health-damaging behaviours by socioeconomic groups. Behaviours such as eating processed foods, foods high in sugar and foods prepared outside the home, for example, are related to individuals’ socioeconomic status and associated with an increased risk of obesity and associated NCDs.

What Was Discovered…

WCBA from wealthier households bear a higher burden of obesity and overweight than their less wealthier counterparts, which increased between 1998 and 2016. The main contributors to socioeconomic inequality in overweight and obesity were socioeconomic status, age and urban residence. While the contributions of race groups and urban residence were more prominent for the changes in socioeconomic inequality in overweight and obesity among WCBA, SES and race were the most prominent for the urban/rural sub-analysis.

Also, as reported in South Africa, obesity could be more evenly spread among women, irrespective of their socioeconomic class, compared to men. Significant factors that explain socioeconomic inequalities in overweight and obesity, especially in the general population, include wealth, alcohol consumption and smoking habits, occupational status, educational attainment, residency status, sedentary lifestyle, physical inactivity, and marital status.

Overweight and obesity prevalence among WCBA increased in South Africa, but associated socioeconomic inequality remained unclear. To the best of our knowledge, this study was the first to report on the changing patterns in the socioeconomic inequality in overweight and obesity among South African non-pregnant WCBA (and indeed in Africa) and factors explaining these changes in socioeconomic inequality between 1998 and 2016. Overweight and obesity occur more among WCBA from wealthier backgrounds in South Africa. Our paper, focusing on non-pregnant WCBA, reported concentration indices similar to those reported previously for women in general, meaning that there are few differences between the general adult female population and the non-pregnant WCBA in terms of socioeconomic inequalities in obesity.

In keeping with previous studies, we also find that socioeconomic status was a major contributor to socioeconomic inequality in overweight and obesity among WCBA in 1998 and 2016. Age also plays an important role in explaining the socioeconomic inequality in overweight and obesity among WCBA in 1998 and 2016. In the context of age, the critical reproductive period often leads to nonlinearities in accumulating inequality. Also, we find that urbanisation, and likely its accompanying stress, was one of the main contributors to obesity inequality. Social differences in health could result from an unequal distribution of psychological risk factors. Factors such as the stress of urbanisation may increase the incidence of chronic diseases of lifestyle (including female obesity).

In urban areas, the results of this study show race as a major contributor to the changes in socioeconomic inequality in obesity and overweight compared to socioeconomic status as a major contributor in rural areas. Besides that, education was one of the main contributors to socioeconomic inequality in obesity among WCBA in 1998 and 2016. By examining the changes in socioeconomic inequality in overweight and obesity, we find a pro-rich shift between 1998 and 2016 (i.e., overweight and obesity increasingly being concentrated among women from wealthier backgrounds) for WCBA in South Africa. This was consistent for urban and rural locations. Oaxaca decomposition results showed that the significant contributors to changes in socioeconomic inequality in overweight and obesity between 1998 and 2016 were race (self-identified as black), urban residence and lifestyle (smoking). Employment status was also significant for changes in overweight inequality but not for obesity.

Women without formal educational qualifications tend to be more physically inactive. Also, higher-educated women are employed with better-paying jobs and choose more expensive but not always healthier food products since consuming such items might be a sign of prestige. Because smoking is more prevalent among women from wealthier households (the concentration indices for smoking computed in this study were positive), reducing smoking incidence, especially among wealthier populations, will reduce the pro-rich changes in obesity and overweight inequality among WCBA in South Africa.

The Future/ Possible Solutions…

Women from all socioeconomic backgrounds, especially those from poorer backgrounds, should be prioritised to reduce disparities in overweight and obesity among WCBA in South Africa, recognising the social determinants of health inequality reported in this paper. Cost effective interventions to tackle overweight and obesity include the current tax on sugar-sweetened beverages, reducing taxes or subsidising fruit and vegetables, promoting food labelling and regulating food formulation addressing the availability and affordability of fruits and vegetables, even though they are zero-rated from value-added tax.