Abstract

BACKGROUND: Milk/dairy consumption has been linked to a decreased risk of colon cancer (Huncharek M 2009). But lactose has been linked to an increased risk of ovarian cancer (Genkinger JM 2006), and dairy/milk has been inconsistently linked to an increased risk of prostate cancer (Huncharek M 2008; Qin LQ 2007). This raises questions about the relation with total cancer. Until now, no systematic review looked at the association with total cancer.
OBJECTIVES:

• To review all prospective studies which published information about total dairy, milk, and other dairy products in relationship with total cancer risk and mortality/survival.
• To define the amount of consumption found to be related with possible effects on total cancer.
• To define possible effect modification by confounders.

DATA SOURCE: The Pubmed database was searched (No start date - May 25th, 2010) for relevant articles using the keywords "butter, cheese, cream, dairy, dietary calcium, dietary fat, lactose, margarine, milk, saturated fat, or yoghurt" combined with "prospective, cohort, follow-up, or longitudinal". The exact search term is described Here.
Prospective studies published in the English language were included. Reference lists were searched for additional articles.
RESULTS: 16 articles were found which provided information about 14 different cohorts. Of these, 0 articles were excluded.
Results are described when any evidence for an association - as defined in the Methods - was found. In addition, data about total dairy & milk is described.

• Total disease risk.
  -Data about total dairy was provided by 5 cohorts, including 61,695 cases. No evidence was found for an association.
  -Data about milk was provided by 3 cohorts, including 4,146 cases. No evidence was found for an association.
• Mortality risk.
  -Data about total dairy was provided by 3 cohorts, including 15,300 cases. No evidence was found for an association.
  -Data about milk was provided by 6 cohorts, including 21,331 cases. No evidence was found for an association.

CONCLUSION: No evidence was found for an association between either total dairy consumption, or any specific dairy item (including milk, cheese, yoghurt, [ice] cream, butter, and margarine) and total cancer risk or total cancer mortality. The evidence did not change when cancer risk and cancer mortality were considered one end point.
Also, no evidence was found for effect modification (e.g., by dairy fat), or for a different effect between butter and margarine.
LIMITATIONS: The total amount of cohorts that provided information about the associations examined, was fairly small. Data about total dairy came from US/European cohorts only, while data about milk and yoghurt came from predominantly Japanese cohorts. Still, a fairly consistent lack of an association was found.

|References:
-Genkinger JM. Dairy products and ovarian cancer: a pooled analysis of 12 cohort studies. Cancer Epidemiol Biomarkers Prev. 2006 Feb;15(2):364-72 Full text
-Huncharek M. Colorectal cancer risk and dietary intake of calcium, vitamin D, and dairy products: a meta-analysis of 26,335 cases from 60 observational studies. Nutr Cancer. 2009;61(1):47-69. Abstract
-Huncharek M. Dairy products, dietary calcium and vitamin D intake as risk factors for prostate cancer: a meta-analysis of 26,769 cases from 45 observational studies. Nutr Cancer. 2008;60(4):421-41. Abstract
-Qin LQ. Milk consumption is a risk factor for prostate cancer in Western countries: evidence from cohort studies. Asia Pac J Clin Nutr. 2007;16(3):467-76. Abstract |

Total dairy and total cancer.

Total cancer risk.

5 articles, providing information about 5 different cohorts were found, including 61,695 cases.
Results: A nonsignificant protective effect (trend) was found in 1 cohort (11), and in another cohort among women only (13). No other associations were found.
Effect modification: No data was found.
Conclusion: No significant associations were found. No evidence was found for an association between dairy consumption and total cancer risk (Excluding incomplete data from McCullough ML [5]: Average RR = 1.01).

Total cancer mortality.

3 articles, providing information about 3 different cohorts were found, including 15,300 cases.
Results: No associations were found.
Effect modification: Data about effect modification was provided by one cohort (14). Similar results were found for intakes of low- and full fat dairy products.
Conclusion: No associations were found. No evidence was found for an association between dairy consumption and total cancer mortality (Average RR = 1.00).

Milk and total cancer.

Total cancer risk.

3 articles, providing information about 3 different cohorts were found, including 4,146 cases.
Results: 2 out of 3 cohorts examined the effect of childhood milk consumption (8, 11). One cohort examined the association with unpasteurized milk (8), while in the other cohorts predominantly whole milk was consumed (3, 11). A significant protective effect (trend) was found in one cohort (11). No other associations were found.
Effect modification: Data about effect modification was provided by one cohort (3). Associations did not differ significantly between sexes.
Conclusion: Data was provided about predominantly whole milk. A significant protective effect was found in one cohort. No other associations were found. No evidence was found for an association between milk consumption and total cancer risk (Average RR = 0.92).

Total cancer mortality.

6 articles, providing information about 6 different cohorts were found, including 21,331 cases.
Results: Only one out of these 6 cohorts existed of a non-Japanese population (14). A small, significantly increased risk was found in one cohort (2). No other associations were found.
Data from a 7th cohort was available where the association with "total cancer mortality other than from lung cancer" was examined (See extended version of the table). No significant association was found in this cohort, and no significant association was found with lung cancer mortality (6).
Effect modification: Data about effect modification was provided by one cohort (4). No difference in effect was found between whole-, semiskimmed-, and skimmed milk.
Conclusion: A small, but significantly increased risk was found in one cohort. No other associations were found. No evidence was found for an association between milk consumption and total cancer mortality (Excluding Ikeda M [1], and Bonthuis M [14] because of incomplete data: Average RR = 1.04).