Evaluation of relationships among national colorectal cancer mortality rates, genetic lactase non-persistence status, and per capita yearly milk and milk product consumption

The Diverse Forms of Lactose Intolerance and the Putative Linkage to Several Cancers

Lactase-phlorizin hydrolase (LPH) is a membrane glycoprotein and the only β-galactosidase of the brush border membrane of the intestinal epithelium. Besides active transcription, expression of the active LPH requires different maturation steps of the polypeptide through the secretory pathway, including N- and O-glycosylation, dimerization and proteolytic cleavage steps. The inability to digest lactose due to insufficient lactase activity results in gastrointestinal symptoms known as lactose intolerance. In this review, we will concentrate on the structural and functional features of LPH protein and summarize the cellular and molecular mechanism required for its maturation and trafficking. Then, different types of lactose intolerance are discussed, and the molecular aspects of lactase persistence/non-persistence phenotypes are investigated. Finally, we will review the literature focusing on the lactase persistence/non-persistence populations as a comparative model in order to determine the protective or adverse effects of milk and dairy foods on the incidence of colorectal, ovarian and prostate cancers.

Adult lactose digestion status and effects on disease

BACKGROUND

Adult assimilation of lactose divides humans into dominant lactase-persistent and recessive nonpersistent phenotypes.

OBJECTIVES

To review three medical parameters of lactose digestion, namely: the changing concept of lactose intolerance; the possible impact on diseases of microbial adaptation in lactase-nonpersistent populations; and the possibility that the evolution of lactase has influenced some disease pattern distributions.

METHODS

A PubMed, Google Scholar and manual review of articles were used to provide a narrative review of the topic.

RESULTS

The concept of lactose intolerance is changing and merging with food intolerances. Microbial adaptation to regular lactose consumption in lactase-nonpersistent individuals is supported by limited evidence. There is evidence suggestive of a relationship among geographical distributions of latitude, sunhine exposure and lactase proportional distributions worldwide.

DISCUSSION

The definition of lactose intolerance has shifted away from association with lactose maldigestion. Lactose sensitivity is described equally in lactose digesters and maldigesters. The important medical consequence of withholding dairy foods could have a detrimental impact on several diseases; in addition, microbial adaptation in lactase-nonpersistent populations may alter risk for some diseases. There is suggestive evidence that the emergence of lactase persistence, together with human migrations before and after the emergence of lactase persistence, have impacted modern-day diseases.

CONCLUSIONS

Lactose maldigestion and lactose intolerance are not synonymous. Withholding dairy foods is a poor method to treat lactose intolerance. Further epidemiological work could shed light on the possible effects of microbial adaptation in lactose maldigesters. The evolutionary impact of lactase may be still ongoing.

Impact of lactose containing foods and the genetics of lactase on diseases: an analytical review of population data

Dairy foods (DFs) contain complex ingredients that could affect different diseases. The control of lactose digestion phenotypically divides populations into those who can [lactase persistent (LP)] and those who cannot [lactase nonpersistent (LNP)] assimilate lactose. LNP subjects, however, can adapt to lactose intolerance through intestinal bacteria. The DF/LNP status interactions may function as disease risk modifiers. We evaluated the relationship between DF and LNP with colorectal, breast, prostate, ovarian, lung, and stomach cancer and inflammatory bowel diseases (IBD; Crohn's disease and ulcerative colitis). Yearly per capita DF consumption, LNP national prevalence, cancer mortality, and incidence of IBD were obtained from several sources. A negative binomial regression model was used to derive incremental risks. There were statistically significant (P <or= 0.05) increases in risk for colorectal and prostate cancer and ulcerative colitis with DFs and a statistically significant decreased risk for stomach cancer. There were trends (P<0.1) for lung and ovarian cancers and Crohn's disease. As LNP prevalence increased, stomach cancer risk increased, whereas risks of all other conditions decreased (P<0.01). In 3 cancers (prostate, ovarian, and breast), meta-analyses of case-based studies support ecological data. In colorectal cancer, on the contrary, meta-analyses of case-based studies suggest protection. The possible importance of distinguishing LNP/LP status in studies is discussed.