Possible Health Benefit of Lactose Intolerance: Protection Against Colorectal Cancer

The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 9 No. 4 • December 2006

Possible Health Benefit of Lactose Intolerance: Protection Against Colorectal Cancer

For those with lactose intolerance (of whom Sandy is one; she developed it in her late 50s), it is a condition of inconvenience (since it limits consumption of milk, cheese, and other dairy products) and annoying symptoms (bloating and flatulence). It had occurred to Sandy recently that undigested lactose reaching the large intestine might serve as a prebiotic that causes gas (primarily hydrogen and carbon dioxide) and bloating as a result of fermentation by microbes, just as other undigested carbohydrates (such as resistant starches) do. A 2006 paper1 proposes the same, suggesting that the differential response to dairy products between those with lactose tolerance and those without it could explain discrepancies in studies of the protective effects of dairy products against the development of colorectal cancer.

Since data concerning the status of individual subjects’ lactose tolerance was not available, the authors estimated the impact of this factor by using national prevalences of lactose intolerance, data available from several sources. They divided countries into three subgroups: those countries with low lactose-intolerance status [≤20%; North America (except Mexico), Northwest Europe, some Eastern European countries, and Australia]; those with high lactose-intolerance status [≥80%; included only Asians (China, Japan, Thailand, and their descendants who were singled out in studies coming from North America)]; and middle lactose-intolerance status (21–79%; included southern Europe, the Middle East, some western European countries, such as France, and South America).

The results of their analysis of 80 studies (27 cohort, 53 case-control) showed that in the high lactose-intolerance Asian populations, there was low dairy intake but a generally protective effect (RR = 0.84, 95% CI = 0.73–0.97) of dairy consumption on colon and rectal cancer (several papers were cited). In studies of areas with low lactose intolerance and high dairy consumption (North America, Australia, and northwest Europe), there was again a protective effect of dairy food consumption (RR = 0.80, 95% CI = 0.73–0.88). The authors’ meta-analysis of the mixed populations (which included both high and low lactose-intolerance groups, thus giving an overall middle lactose-intolerance level), resulted in a nonsignificant protective effect of dairy consumption (RR = 0.92, CI = 0.79–1.06).

The authors propose that calcium from dairy consumption may not be consumed in large enough amounts in the high lactose-intolerant and middle lactose-intolerant populations to provide protection but that, in the high lactose-intolerant populations, protection is achieved by low dairy consumption because the lactose “. . . is not digested, reaches the colon, and therefore is a potential prebiotic. If true, it would promote the growth of bacteria (lactobacilli, bifidobacteria) that have been linked in experimental studies with colorectal cancer protection. There is at least one study that reports favorable bacterial promotion by lactose in 22 LNP [lactose-intolerant] Japanese subjects.* Further, there is evidence that regular modest intake of lactose in LNP subjects results in an inverse dose response of breath hydrogen [produced by gut bacteria] on lactose challenge testing.” The authors therefore propose that lactose-tolerance status is an effect modifier rather than a confounder and that future studies of the effects of dairy consumption in mixed populations would be expected to show a protective effect of dairy consumption if they adjust for individual lactose tolerance.

*Ito and Kimura. Influence of lactose on faecal microflora in lactose maldigesters. Microbiol Ecol Health Dis 6:73-6 (1993). For example, the ingestion of 15 g of lactose (as would be found in 330 ml, a little over 1 1/3 cup, of milk) per day for 6 days resulted in significantly increased numbers of lactobacilli, and the numbers of C. perfringens, an important human and animal pathogen, decreased from 81% to 45% of total microflora.


  1. Szilagyi et al. The effect of lactose maldigestion on the relationship between dairy food intake and colorectal cancer: a systematic review. Nutr Cancer 55(2):141-50 (2006).

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