Dairy Products Contribute to Cancer Risk

This letter was published in the April, 2005, issue of the Journal of the National Medical Association.

To the Editor:

I read with interest your supplementary report “The Role of Dairy and Dairy Nutrients in the Diet of African Americans” (J Natl Med Assoc. 2004 (suppl);96:5S-32S.). I was dismayed, however, to observe that the report excluded research showing that dairy products contribute to cancer risk, especially prostate and ovarian cancer, and minimized the problems associated with digesting dairy products.

Since African American men have the highest prostate cancer prevalence and death rates of any group in the United States, and since African American women have lower overall age-adjusted cancer survival rates compared to whites, this omission does our patients a grave disservice. In addition, individuals with lactase nonpersistence experience very real discomfort. To downplay their level of discomfort works against empowering them to take a proactive role in their personal health. While adequate intake of many of the nutrients – most notably calcium – contained in dairy products and other foods is important, strong evidence suggests that dairy products should not be a recommended source for these nutrients, especially for African Americans. Let us consider the evidence in greater detail.

For African American men, prostate cancer is the second leading cause of cancer deaths and fourth leading cause of death from all causes.¹ Given these sobering statistics, it is important to note that at least 11 human population studies have linked dairy product consumption and prostate cancer, according to a review by the World Cancer Research Fund and the American Institute for Cancer Research.² Additionally, in the Physician’s Health Study, the relationship between dairy product consumption and prostate cancer was investigated among 1,012 men with prostate cancer after 11 years of follow-up. Compared with men consuming less than 0.5 daily servings of dairy products, men who consumed more than 2.5 servings per day had a 32% greater risk of prostate cancer.³

As our research indicates, African American women with advanced epithelial ovarian cancer have been found to receive less aggressive treatment, are more often diagnosed with advanced stage disease, and have lower survival rates than white women.⁴ Since the prognosis of African American women with epithelial ovarian cancer is extremely poor, and since recent studies have found a relationship between dairy consumption and epithelial ovarian cancer, African American women would do well to avoid dairy products. In a prospective study looking at ovarian cancer risk in 80,326 women in the Nurses’ Health Study, researchers found an increased risk for serous epithelial ovarian cancer among the highest lactose consumers. Skim and low-fat milk were the largest contributors of lactose to these women’s diets.⁵ In another cohort study of 61,084 women in Sweden, researchers found that high intakes of lactose and dairy were associated with an increased risk of serous epithelial ovarian cancer. Women who consumed just two glasses of milk per day or at least four daily servings of dairy products had twice the risk of developing serous epithelial ovarian cancer compared to women who consumed fewer than two servings of dairy a day.⁶ These findings raise a red flag for dairy consumption since “serous” cancer is the most common histologic subtype of all the epithelial ovarian cancers diagnosed in women, regardless of race or ethnicity.

Lactase nonpersistence, the inability to digest lactose, is not merely a matter of cultural “food preferences and misconceptions,” as the report suggests, but is well established in the literature as a true physiological response to lactose. As the report notes, repeated studies have found that lactase nonpersistence occurs in a majority of African Americans. The report emphasizes that Suarez, et al. (1997), found that “lactose maldigesters can comfortably consume one cup of milk with breakfast or two cups of milk in divided doses.” (p. 20S) However, it was not reported that in this dairy industry-sponsored study, only three of the subjects were African American and close to half the original subjects would not go on to complete more than one lactose tolerance test.⁷ Furthermore, a double-blind randomized study found that symptoms of lactose maldigestion could occur after just a 12 g dose, which is the amount in one cup of milk.⁸

The report suggests that African-Americans with lactase nonpersistence should build up a tolerance to dairy products. The majority of African Americans are lactose non-digesters. It is irresponsible to assume that they will eventually tolerate the digestive discomfort from lactose if they simply consume more lactose from dairy. This is especially problematic as the evidence mounts that dairy may contribute to cancer risk.
To suggest that African Americans should spend more on products like Lactaid and lactase supplements to ease dairy product consumption only imposes needless burdens on the public. Given the evidence on dairy for cancer risk and the difficulty digesting lactose among a majority of African Americans, dairy products are not a healthy choice or one that should be encouraged in this population. This is especially true since there are readily available, inexpensive, and whole-foods sources of the nutrients found in milk. The most healthful calcium sources are green leafy vegetables and legumes. Broccoli, Brussels sprouts, collards, kale, mustard greens, and a wide variety of legumes are loaded with highly absorbable calcium, fiber, and a host of other healthful nutrients. These foods fit comfortably into African American culinary traditions and do not contain cholesterol, saturated fat, or cause digestive problems among individuals with lactase nonpersistence.

Sincerely,
Groesbeck P. Parham, M.D.
Professor of Gynecologic Oncology and Preventive Medicine
University of Alabama at Birmingham

References:
1. CDC, 1998
2. World Cancer Research Fund/American Institute for Cancer Research. Food, Nutrition, and the Prevention of Cancer: A Global Perspective. American Institute for Cancer Research. Washington, D.C., 1997, p. 461.
3. Chan J, Stampfer M, Ma J, et al. Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study. Am J Clin Nutr. 2001 Oct;74(4):549-54
4. Parham G, Phillips JL, Hicks ML, et al. The National Cancer Data Base report on malignant epithelial ovarian carcinoma in African-American women. Cancer. 1997 Aug 15;80(4):816-26.
5. Fairfield KM, Hunter DJ, Colditz GA, et al. A prospective study of dietary lactose and ovarian cancer. Int J Cancer. 2004 Jun 10;110(2):271-7.
6. Larsson SC, Bergkvist L, Wolk A. Milk and lactose intakes and ovarian cancer risk in the Swedish Mammography Cohort. Am J Clin Nutr. 2004 Nov;80(5):1353-7.
7. Bertron P, Barnard ND, Mills M. Racial bias in federal nutrition policy, Part I: The public health implications of variations in lactase persistence. J Natl Med Assoc. 1999 Mar;91(3):151-7.
8. Hertzler SR, Huynh BCL, Savaiano DA. How much lactose is low lactose? J Am Dietetic Asso 1996;96:243-6.