Approximately 60 to 70 per cent of people in India are lactose intolerant. The frequency is higher among healthy populations from southern India than from northern India. The lower frequency in the north Indians is apparently due to the fact that they are descendants of the Aryans who have been dairying for long and are known to be lactose tolerant. So, the genetic mixing is responsible for greater lactose tolerance amongst them.
Europeans have higher percentage of lactose absorption in the whole world. People of African, Asian, African-American have lower frequency of lactose absorption and are most likely to be affected at an earlier age. The absorption capacity goes on decreasing as we grow up. It is least in old age.