About the WCRF: In October 2007 the WCRF (World Cancer Research Fund) published a systematic review of all available literature relating cancer to various aspects of our diet (1). Though they systematically reviewed the available literature, they did not systematically publish all findings:
1) Data relating dietary aspects to cancer often was not published for all cancer types.
2) Published data was often limited to major food groups. Rarely any data was published relating specific items of our diet to cancer risk, while an abundant amount of data does exist.
I created a systematic review of socalled "prospective studies" (also called cohort studies) (2). These are studies in which large groups of people (sometimes multiple hundreds of thousands per study) filled in a food frequency questionnairy. Thereafter, these subjects are followed-up for years to find out how many of them develop specific diseases. Prospective studies are the most reliable form of clinical evidence (3) since "randomized trials" (4) are close to impossible to do for dietary aspects.
BACKGROUND: The WCRF (2007) found a probable protective effect of milk against colorectal cancer, and limited evidence suggesting that cheese is a cause of colorectal cancer. For eggs, the evidence was too limited in amount, consistency, or quality to draw any conclusions. No other data about dairy items or eggs was provided. OBJECTIVE: To review all prospective studies which published information about:
a) total dairy,
c) or specific dairy items,
and their relationship with colorectal, colon, and rectum cancer. DATA SOURCE: I searched the Pubmed database (January 1966 to December 14, 2007) for relevant studies using any of the following keywords: dairy, milk, yoghurt, cream, egg, eggs, cheese, butter, margarine, diet, and dietary combined with the word cancer. Prospective studies published in the English language were included. RESULTS: Data about 25 cohorts met the inclusion criteria: 1) Total disease risk.
-Ten studies (11 cohorts) combining 5,321 cases provided information about total dairy in relation to colorectal cancer risk. Though most RRs for total dairy were < 1, significance was reached in only 2 studies combining 1,379 cases. No evidence was found that total dairy fat increases colorectal cancer risk among 4 studies.
-A pooled analysis of 10 studies and an additional 9 studies (8.980 cases) provided information about total milk in relation to colorectal cancer risk. No study found any significantly or nonsignificantly increased risk. Data of studies which stratified risk by cancer site (colon vs rectum) is presented: The pooled analysis and 4 out of 5 studies found a protective effect against colon cancer risk. The pooled analysis found a significant protective effect against rectal cancer risk, but the remaining 3 studies did not.
-A pooled analysis of 9 studies and an additional 6 studies (5,198 cases) provided information about cheese in relation to colorectal cancer risk. Of total cheese, the pooled analysis found a weak increased colorectal cancer risk which tended to be stronger for colon than for rectal cancer. Two out of the remaining five studies found an increased colon cancer risk. But of cottage cheese, the pooled analysis and both remaining studies found a decreased colorectal cancer risk.
-A pooled analysis of 8 studies and an additional 3 studies (4,681 cases) provided information about yoghurt in relation to colorectal cancer risk. No study found any significant or nonsignificant association with risk.
-Data about butter and cream in relation to colorectal cancer is limited (A pooled analysis for butter/A pooled analysis and 1 additional study for cream). No significant relations were found in the pooled analysis.
-Four studies provided information about eggs in relation to colorectal. Though all available RRs were above 1, no study found a significantly increased risk. 2) Advanced-stage disease risk.
No prospective study provided information about any of the variables in relation to advanced-stage or metastatic cancer risk. 3) Mortality risk.
-One study provided information about dairy products (defined as milk + ice cream) in relation to colorectal cancer mortality. It found a nonsignificantly decreased risk.
-Three studies provided information about milk in relation to colorectal cancer mortality. No study found a significant association.
-Two studies privided information about cheese in relation to colorectal cancer mortality. One of the studies found an increased female rectal cancer mortality risk.
-One study provided information about yoghurt in relation to colorectal cancer mortality. It found a decreased male rectal cancer mortality risk.
-Three studies provided information about eggs in relation to colorectal cancer mortality. Two studies found an increased trend in total colorectal cancer mortality. The remaining study found an increased male colon cancer mortality risk only. CONCLUSION: Prospective studies suggest that total dairy may decrease colorectal cancer risk. A probabe protective effect of total milk against rectal cancer - and even more consistently - against colon cancer risk is suggested. Total cheese may increase colon cancer risk, while there is consistent evidence that cottage/ricotta cheese decreases colorectal cancer risk. No association between yoghurt and colorectal cancer risk is found consistently. Data of the relation between butter,cream or eggs and colorectal cancer risk is to limited to come to a conclusion.
Little data is available about colorectal cancer mortality. It is possible that eggs increase mortality risk.