Previous epidemiological studies have revealed that obesity is a risk factor for several types of cancers, including those affecting the esophagus, colon/rectum, breast, kidney, liver, ovary, and pancreas. Although the burden of obesity-related cancers is highly prominent in the sixteen Southern African Development Community (SADC) countries, their time trends are unknown. 

A recent Preprints with the Lancet study addresses this research gap using data from the 2019 Global Burden of Diseases (GBD) Study for the analysis.

Study: Trends in the Burden of Obesity-Related Cancers in SADC Countries, 1990-2019: Findings from the Global Burden of Disease Study. Image Credit: Fuss Sergey / Shutterstock.com

Background

Previous studies have established a causal relationship between obesity and cancer incidence. For example, the relative risk (RR) for esophageal adenocarcinoma is high for individuals with a BMI of 40 kg/m² or more. However, in most developing countries, the number of cancer-related studies and BMI is extremely low.

The sixteen countries that form the SADC include South Africa, Mozambique, Seychelles, Eswatini, Comoros, Angola, Democratic Republic of Congo (DRC), Botswana, Malawi, Namibia, Mauritius, Lesotho, Madagascar, Tanzania, Zimbabwe, and Zambia. Unfortunately, these countries do not have sufficient information regarding the morbidity and mortality trends linked to obesity-related cancers.

The International Agency for Research on Cancer’s Global Cancer Observatory (GLOBOCAN) study reported that, among all cancer types, breast and colorectal cancers are the most diagnosed, while liver and stomach cancers are the most common causes of death.

In 2020, the GLOBOCAN study estimated 1.1 million new cases and 711,429 deaths due to neoplasms in Africa. This study further projected that by 2040, the burden of all neoplasms will increase significantly, with 1.4 million deaths in Africa alone. In the last 30 years, a significant increase in the prevalence of obesity in adult females and males has been observed.

About the study

GBD data is available on the websites of the Institute for Health Metrics and Evaluation at the University of Washington Seattle. GBD obtained data from verbal autopsies, vital registration, and International Classification of Diseases (ICD) codes for the years 1990 and 2019.

To estimate mortality due to individual cancer types, scientists used the Cause of Death Ensemble Model and Spatio-Temporal Gaussian regression. In addition, each type of cancer was systematically searched on Medline.

The slopes of the mortality rate between 1990 and 2019 were assessed using the annualized age-standardized rate of change (AROC). This analysis helped identify changes in mortality rates due to different types of cancer.

A positive AROC suggests an increasing mortality rate over 30 years, while a negative AROC reflects decreasing mortality rates. Uncertainties for each outcome were determined using 95% uncertainty intervals (UIs) using 1,000 bootstrap draws from the posterior distribution.

Study findings

Mortality due to breast cancer was significantly higher as compared to other cancer types, such as gallbladder/biliary tract and thyroid. Overall, negative AROCs in males and females for esophageal and leukemia cancers were obtained, thus indicating that mortality due to these cancers is trending in the right direction.

The increased burden of obesity-related cancers in SADC during the study period could be due to the epidemiological transition. Herein, there was an increased tendency of the population to shift from contracting primarily communicable diseases to developing non-communicable diseases. 

The shift in the disease pattern has been attributed to changes in lifestyle, environmental exposure, diet, and an increase in healthcare services. Another theory of this shift is linked to the demographic transition theory, in which aging populations are associated with a greater risk of cancer. Moreover, demographic transition proposes that neoplasms manifest in middle and old age.

African governments, especially in the SADC, require investments to prevent cancer and early disease diagnosis. Additional investments are needed to provide cancer care services.

Currently, the demand for cancer care has increased in many low-income countries. The authors recommend that limiting the marketing of unhealthy food, promoting healthy diets, and raising risk awareness could assist in controlling obesity and, as a result, reduce the burden of high-BMI-related cancers.

Based on a high volume of evidence, SADC countries also need to invest in surgical cancer care services. Consistent with the findings of the GLOBOCAN 2020 study, the current study indicates an urgent need for a holistic approach to managing obesity-related cancer incidence.

Conclusions

The current study presents the most comprehensive estimates of the burden of cancer due to obesity in SADC countries. It is imperative to understand the trends in the obesity-related cancer burden in each of the 16 SADC countries, as this knowledge will help develop informed strategies and interventions to reduce the burden. 

Journal reference:

• Preliminary scientific report. Gona, P., Gona, C. M., Ballout, S., et al. (2023) Trends in the Burden of Obesity-Related Cancers in SADC Countries, 1990-2019: Findings from the Global Burden of Disease Study. Preprints with the Lancet.  doi:10.2139/ssrn.4455300