Simplify the following text for a Grade 9 native English-speaking person.
Original: The frequency of decreased lactase activity ranges from as little as 5 % in northern Europe , up to 71 % for Sicily , to more than 90 % in some African and Asian countries .
Simplified: This decrease of activity ranges from 5 % in northern Europe , to over 71 % in Sicily and to over 90 % in parts of Africa and Asia .