BACKGROUND:
Underweight is a public health issue that affects children in low-middle income countries. It is defined as low weight for age measured by -2 standard deviation (World Health Organization, 2016). This study aimed to investigate the socio-demographic factors associated with underweight among children under five years of age in SADC countries.

METHODS:
The study used four Demographic and Health Surveys conducted in Lesotho (2014), Malawi (2015-16), South Africa (2016) and Zambia (2018). The study population consisted of children under the age of five years: 1869 in Lesotho, 5786 in Malawi, 1416 in South Africa and 9689 in Zambia. Chi-square test and logistic regression were used to establish social and demographic factors associated with underweight.

RESULTS:
Factors such as child’s age, child’s sex, birth weight, mother’s educational level, and household income were found to be the most predominant determinants of underweight among children under five years. For example, the study found that in Malawi children aged 36-47 months and 48-59 months were OR= [1.57 95% CI: 1.12-2.22] and OR= [1.54 95 % CI: 1.09-2.17] more likely to be underweight as compared to children 0-11 months old. Moreover, in Lesotho male children were OR= [1.52 95% CI: 1.05-2.19] more likely to be underweight as compare to female children.

CONCLUSIONS:
The prevalence of underweight recorded in this study was 10.3% in Lesotho, 11.7% in Malawi, 11.8% in Zambia and 5.9% in South Africa respectively, further demonstrating that underweight continues to be a health issue affecting children under five years. Therefore, the study recommends that the predominant factors found in this study should be considered when designing programs aimed at improving child underweight. It is further suggested that future intervention programs should follow a multi-sectoral approach targeting the individual, household, and community factors.