High- and Low-fat Dairy Intake, Recurrence, and Mortality After Breast Cancer Diagnosis

Candyce H. Kroenke; Marilyn L. Kwan; Carol Sweeney; Adrienne Castillo; Bette J. Caan

Disclosures

J Natl Cancer Inst. 2013;105(9):616-623. 

In This Article

Abstract and Introduction

Abstract

Background Dietary fat in dairy is a source of estrogenic hormones and may be related to worse breast cancer survival. We evaluated associations between high- and low-fat dairy intake, recurrence, and mortality after breast cancer diagnosis.

Methods We included 1893 women from the Life After Cancer Epidemiology study diagnosed with early-stage invasive breast cancer from 1997 to 2000, who completed the Fred Hutchinson Cancer Research Center Food Frequency Questionnaire after diagnosis. A total of 349 women had a recurrence and 372 died during a median follow-up of 11.8 years, with 189 deaths from breast cancer. We used delayed entry Cox proportional hazards regression to evaluate associations between categories of the cumulative average of dairy fat at baseline and at follow-up 5 to 6 years later and subsequent outcomes. Tests of statistical significance were two-sided.

Results In multivariable-adjusted analyses, overall dairy intake was unrelated to breast cancer–specific outcomes, although it was positively related to overall mortality. Low-fat dairy intake was unrelated to recurrence or survival. However, high-fat dairy intake was positively associated with outcomes. Compared with the reference (0 to <0.5 servings/day), those consuming larger amounts of high-fat dairy had higher breast cancer mortality (0.5 to <1.0 servings/day: hazard ratio [HR] = 1.20, 95% confidence interval [CI] = 0.82 to 1.77; and ≥1.0 servings/day: HR = 1.49, 95% CI = 1.00 to 2.24, P trend = .05), higher all-cause mortality (P trend < .001), and higher non–breast cancer mortality (P trend = .007); the relationship with breast cancer recurrence was positive but not statistically significant. The higher risk appeared consistent across different types of high-fat dairy products.

Conclusions Intake of high-fat dairy, but not low-fat dairy, was related to a higher risk of mortality after breast cancer diagnosis.

Introduction

Many studies[1–14] have evaluated whether dairy intake is related to breast cancer; results are equivocal.[15] A recent meta-analysis of prospective cohort studies found a modest inverse association of dairy intake and breast cancer risk, but study heterogeneity was high.[16] Individual studies have shown positive,[12] inverse,[4,6,7,10,11] and null[1,2,9,14,17] associations. One study found that associations varied by levels of fat; greater consumption of high-fat dairy intake was positively related whereas consumption of low-fat dairy intake was inversely related to breast cancer risk.[8] Researchers have hypothesized a variety of mechanisms through which dairy might influence breast cancer risk, including calcium, vitamin D, insulin-like growth factors,[18,19] conjugated linoleic acid,[20] and estrogenic hormones.[21] Equivocal findings could be related to the counteracting effects of a multiplicity of factors that may act on breast cancer. However, because estrogens are considered the major etiologic pathway to breast cancer, the influence of dairy intake on estrogens should be strongly considered in understanding how dairy affects breast cancer–specific outcomes.

The Melbourne Collaborative Cohort Study, which included women from Australia, New Zealand, the United Kingdom, Italy, and Greece, found that dairy intake was statistically significantly related to higher levels of estradiol and free estradiol.[21] Ganmaa and Sato hypothesized that estrogen and progesterone levels are markedly elevated in dairy products consumed in the Western world compared with those produced in traditional herding societies because most of the milk in the West is produced by pregnant cows, with production enabled both by genetic modification of dairy cows as well as modifications to their feed.[22,23] However, because estrogenic hormones reside primarily in fat, levels of female hormones may be substantially lower in skim vs whole milk.[24] Insight as to the influence of dairy on breast cancer outcomes may be gained by separately evaluating associations of high- vs low-fat dairy intake and hormonal cancers. Equivocal findings in previous studies could be related to differing patterns of high- and low-fat dairy consumption in different populations and the failure to distinguish high- vs low-fat consumption.

Consistent with this hypothesis, a recent study of dairy intake and prostate cancer survival found that greater consumption of whole milk was associated with worse survival but skim milk was associated with improved survival.[25] No previous studies have evaluated associations of postdiagnosis high- vs low-fat dairy intake and breast cancer survival. We hypothesized that consumption of high-fat, but not low-fat, dairy foods would be related to a higher risk of recurrence and breast cancer mortality. We examined these associations in 1893 women with invasive breast cancer from the Life After Cancer Epidemiology (LACE) Study.

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