Lactose Intolerance

Risk factors

• Age: Lactose intolerance can begin at different times in life. In people of European ancestry, it usually starts to affect children older than 5 years. In African-Americans it can occur as early as age 2. Infants born prematurely may have reduced levels of lactase, since production of this enzyme starts late in the last trimester.
• Ethnicity: Lactose intolerance is highly dependent on ethnicity: 95 percent of Asians, 60 to 80 percent of African Americans and Ashkenazi Jews, 80 to 100 percent of American Indians, and 50 to 80 percent of Hispanics have lactose intolerance. It is least common in people of North-European origin (2-5%).
• Genetics: The ability to digest lactose in adults is inherited as a dominant Mendelian trait. This means that it is caused mainly by your genetic makeup with little or no influence from the environment. A sequence variant (SNP) near the lactase gene has been identified that determines whether people are “lactase persistent” or “lactose intolerant”, that is whether the expression of the gene that controls lactase production is turned on or off during adulthood. This means that your genotype will, with high probability, predict whether you are lactose intolerant or not.

Note however, that even if you turn out to have the variant that enables you to digest lactose during adulthood, you could still have other variants that make you sensitive or even allergic to milk.

It should also be noted that the variant reported here does not account for every case of lactase persistence, particularly in people that trace their ancestry to sub-Saharan Africa. In this part of the world it is thought that other, presently unidentified, variants are also responsible for cases of lactase persistence.

Prevention

Being lactose intolerant or lactase persistent during adulthood depends completely on your body’s ability to produce lactase, which is genetically determined. There is no scientific evidence to indicate that diet or lifestyle has an impact on your ability to produce lactase as an adult. For example, avoiding milk completely for long periods does not lead to a change in lactase production.

However, removing milk products from the diet usually improves the symptoms of lactose intolerance. Milk products that are soured or otherwise treated (like yogurts and solid cheeses) contain relatively low levels of lactose and the soured products may even contain the lactase-producing Lactobacillus Acidophilus. As a result, these milk products cause fewer problems for lactose intolerant people compared to other milk products. Lactose intolerant people who avoid milk products should supplement their diet with calcium-rich food and vitamin D to build up and maintain a healthy bone mass.

Note that having lactose intolerance is not the same as being allergic to milk. Unlike an allergy, lactose intolerance does not involve your immune system and does not necessarily mean that you will have to completely avoid dairy products.

More information

You can find out more information about lactose intolerance by talking to your doctor and visiting these Web sites:

• National Digestive Diseases Information Clearinghouse (NDDIC) on lactose intolerance
• Mayo Clinic information on lactose intolerance
• MedlinePlus article on lactose intolerance
• Wikipedia on lactose intolerance

Scientific references

1. Beja-Pereira, A., Luikart, G., England, P.R., Bradley, D.G., Jann, O.C., Bertorelle, G., Chamberlain, A.T., Nunes, T.P., Metodiev, S., Ferrand, N., & Erhardt, G. (2003). Gene-culture coevolution betweencattle milk protein genes and human lactase genes. Nature Genetics, 35(4), 311-313.
2. Bersaglieri, T., Sabeti, P.C., Patterson, N., Vanderploeg, T., Schaffner, S.F., Drake, J.A., Rhodes, M., Reich, D.E., & Hirschhorn, J.N. (2004). Genetic signatures of strong recent positive selection at the lactase gene. American Journal of Human Genetics, 74(6), 1111-1120.
3. Enattah, N.S., Sahi, T., Savilahti, E., Terwilliger, J.D., Peltonen, L. & Jarvela, I. (2002). Identification of a variant associated with adult-type hypolactasia. Nature Genetics, 30(2), 233-237.
4. Lomer, M.C.E., Parkes, G.C., & Sanderson, J.D. (2008). Review article: lactose intolerance in clinical practice – myths and realities. Alimentary Pharmacology & Therapeutics, 27 (2), 93-103.

This content was last reviewed on February 11, 2010.