The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the NIH estimates that between 30 and 50 million Americans are lactose intolerant, more people than affected by any other digestive disease.

This includes an estimate of lactose intolerance affecting 30 % of Americans overall, 75% of African-Americans and 90% of Asian and Native Americans. (American Dietetic Association http://www.eatright.org/nfs/nfs43.html.

About 3/4 of the world's population is lactose intolerant.

http://www.niddk.nih.gov/health/digest/pubs/ddstats/ddstats.htm

Latest genetics on lactose intolerance: http://www.gastro.org/reuters/2002/jan/14/20020114epid001.html