Genetic and environmental factors associated with lactose digestion in African populations

Impaired lactose digestion, primarily resulting from lactase non-persistence (LNP), is widely observed across African and non-African populations; however, its prevalence differs according to genetic background and dietary practices. Although numerous pastoralist cultures in Africa have independently developed lactase persistence (LP), a sizable portion of the population experiences primary or secondary lactose malabsorption, either as a natural genetic trait or as a secondary impairment resulting from intestinal damage. This review summarizes the genetic variants and environmental contributors associated with lactose digestion in Africa, highlighting ancestry-specific variants and the underrepresentation of African populations in prior studies. A Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020-guided systematic review searched PubMed, African Journals Online, Wiley Online Library, and Google Scholar (1970 to June 2025) for studies on genetic and environmental contributors to lactose digestion in African groups. Inclusion focused on human studies reporting lactase persistence (LP)/LNP or secondary impaired lactose digestion. Data were extracted on variants, diagnostics, and outcomes. Twenty-eight studies were included, predominantly from East African pastoralists (53.3%), where LP alleles, including -13910T and -14010C in MCM6 intron 13, reached frequencies of 40%-43%.Southern or West/North African groups showed LNP rates >70%. Secondary impaired lactose digestion affected 65%-68% of malnourished/infected children, highlighting enteropathy and infections. Genotype-phenotype discrepancies were noted, with statistical associations due to linkage disequilibrium but not direct causation. Impaired lactose digestion in Africa reflects genetic adaptations in pastoralists and environmental stressors like malnutrition. Population-specific diagnostics and interventions are needed, integrating microbiome and dietary research for resource-limited settings.