I've always thought it a little disgusting to drink a liquid that squirts out from another animal's mammary gland, but research suggests my European ancestors have been doing so for centuries. The reason why so many of European heritage (like me) have lactose intolerance has to do with antibiotics. The guts of my ancestors (post-agriculture) evolved bacteria that helped them digest that lactose, which antibiotics eliminate.
There is strong evidence supporting probiotic therapy (1-4). In Japan, there are at least 20 probiotic foods that have health claims (1). And one of the key benefits of probiotics is alleviating symptoms of lactose intolerance (2-3). In fact, our efforts in leading people with lactose intolerance to avoid lactose might change in the future. At least one scientific article has suggested that lactose may have potential prebiotic effects, meaning it could be instrumental to grow probiotic bacteria and inhibit growth of pathogenic bacteria (4;5p54).
1. Farnworth ER. The evidence to support health claims for probiotics. J Nutr 2008;138:1250S-4S.
2. He T, Priebe MG, Zhong Y et al. Effects of yogurt and bifidobacteria supplementation on the colonic microbiota in lactose-intolerant subjects. J Appl Microbiol 2008;104:595-604.
3. Zhong Y, Huang CY, He T, Harmsen HM. [Effect of probiotics and yogurt on colonic microflora in subjects with lactose intolerance]. Wei Sheng Yan Jiu 2006;35:587-91.
4. Szilagyi A. Review article: lactose--a potential prebiotic. Aliment Pharmacol Ther 2002;16:1591-602.
5. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.