Introduction: Colorectal cancer (CRC) is the second leading cause of cancer-related death worldwide. A recent meta-analysis estimated a pooled CRC age-standardized incidence rate of 5.25 per 100,000, though suggested this to be an under-estimate of the true rate. Due to the heterogeneity of dietary and lifestyle practices throughout the continent, our work sought to define risk factors for the development of CRC in Africa.
Methods: We systematically searched PubMed, Embase, Global Health, CINAHL, Cochrane CENTRAL, and African Index Medicus for studies written in English, examining risk factors of CRC in Africa. Meta-analysis was performed to compare different risk factors in constituent studies. Jamovi software was used for statistical analysis utilizing a random-effects model. Analysis of CRC studies was supplemented by estimated relative risk (RR) comparing various risk factors.
Results: Of 2479 studies screened, 149 were included for the quantitative analysis (n=93707). Family history of CRC was associated with a RR of 2.14 and 95% RR CI [1.68-2.72], n=340. Individuals with diets based on high calcium, or vegetable consumption had 45% and 8% lower chances of having CRC, with respective RR of 0.55 [0.44-0.69] and 0.92 [0.84-0.99]. Diets based on carbohydrate, dairy, sugary food/drinks, or meat consumption indicated 14, 31, 43, or 45% higher chances of CRC, and 1.14 [1.03-1.26], 1.31 [1.21-1.42], 1.43 [1.32-1.57], 1.45 [1.36-1.54], n=5303. Physical activity was associated with lower RR of having CRC (81% less), 0.19 [0.15-.26]. Individuals that were obese, have been exposed to carcinogenic chemicals, have history of alcohol use, or tobacco use indicated 43, 45, 54, 65% higher chance of CRC, with 1.43 [1.02-2.03], 1.45 [1.23-1.68], 1.54 [1.28-1.84], 1.65 [1.45-1.9], n=8995. With the exception of family history, there was considerable heterogeneity among studies (I2 > 80%).
Discussion: There are both modifiable and non-modifiable risk factors that are distinct to Africa and vary across the continent. Our review revealed that obesity, carcinogen exposure, tobacco or alcohol use, and diets high in carbohydrates, dairy, and red meat increase CRC risk. On the contrary, high calcium or vegetable-based diets, and physical activity are protective against the development of CRC. Further work is needed to characterize CRC risk factors by region and to understand the impact of risk factor mitigation efforts on the overall incidence of CRC.
