In a review by Gudmand-Hoyer E in published on The American Journal of Clinical Nutrition (1994), [primary lactose deficiency] is lowest in Scandinavia and Northwest Europe (3-8%) and close to 100% in most of Southeast Asia. In Europe the frequency increases in the southern and eastern directions, reaching 70% in southern Italy and Turkey. There is also a high prevalence of lactose maldigestion in the people of Africa with the exception of cattle-raising nomads. Moreover, studies conducted by Scrimshaw and Murray and Sahi review the prevalence of lactose maldigestion globally. The prevalence is above 50% in South America, Africa, and Asia, reaching almost 100% in some Asian countries.
If you look very carefully at the map, though, you will see that the rate of lactose intolerance reaches not just 70% in Sicily but a pan-European high of 81% just north of Napoli (around the lower calf of Italy, above the spur). This region is called Campobasso, and it's where I get my gene for hypolactasia.
