Off the top of my head, I'm not familiar with Vit D surveys in West Africa, but there have been some in East Africa. From these, it looks like lifestyle and die

Off the top of my head, I'm not familiar with Vit D surveys in West Africa, but there have been some in East Africa. From these, it looks like lifestyle and diet are probably the biggest determinants of Vit D levels. For example, the pastoral Masai have phenomenally high levels of Vit D, while a related tribe of agriculturalists have significantly lower levels, with similar sun exposure. Another survey of young healthy urban participants in Nairobi found similarly low to mid levels of Vit D. Among South Indian rural farm workers, who have complexions comparable to the African subjects and similar levels of sun exposure had much less levels of Vit D. It was speculated that phytates in their diet impacted Vit D levels.