In the American South, hookworm infestations are cited as a possible reason for the stereotype's existence: hookworms can cause lethargy and learning disabilities in their victims, and a common vector of infection is people walking barefoot.
Nutrition issues. Lack of certain vitamins and microelements may result in developmental deficiencies (the word "cretinism" originally meant an affliction caused by iodine deficiency, hence the insult "Alpine cretin" in some languages). Living in backwards regions may leave you unable to receive the required amounts of it — for example, when you live in a remote inland region, you will have a hard time getting access to iodine-rich seafood. For this reason, development efforts may involve trying to reach them with the right nutrient fix.
are cited as a possible reason for the stereotype's existence: hookworms can cause lethargy and learning disabilities in their victims, and a common vector of infection is people walking barefoot.