Patients who consume high-fat dairy products following breast cancer diagnosis increase their risk of dying from the disease years later, according to a study by Kaiser Permanente researchers.
The study, published in the Journal of the National Cancer Institute, is the first to examine the relationship between high-fat and low-fat dairy consumption following a diagnosis of breast cancer and long-term breast cancer survival.
Previous studies have shown that higher lifetime exposure to estrogen is a causal pathway to breast cancer. Estrogen levels are believed to be elevated in dairy products consumed in the Western world, because most of its milk comes from pregnant cows. Estrogenic hormones reside primarily in fat, so levels are higher in high-fat than in low-fat dairy products.
The researchers studied a cohort of women who were diagnosed with early-stage, invasive breast cancer between 1997 and 2000, primarily from Kaiser Permanente's Northern California region (83 percent) and the Utah Cancer Registry (12 percent).
Those consuming larger amounts of high-fat dairy (one serving or more per day) had higher breast cancer mortality as well as higher all-cause mortality and higher non-breast cancer mortality.
Women consuming one or more servings per day of high-fat dairy had a 64 percent higher risk of dying from any cause and a 49 percent increased risk of dying from their breast cancer during the follow-up period.
High-fat dairy products included cream, whole milk, condensed or evaporated milk, pudding, ice cream, custard, flan and also cheeses and yogurts that were not low-fat or non-fat.
In general, the women studied reported that they consumed low-fat milk and butter most often, and they consumed relatively limited amounts of low-fat dairy desserts, low-fat cheese and high-fat yogurt. Overall, low-fat dairy intake was greater (median 0.8 servings per day) than high-fat dairy (median 0.5 servings per day).
The study found an association between high-fat dairy and breast cancer mortality, but no association with low-fat dairy products and breast cancer outcomes.
Women entered into the cohort approximately two years after their breast cancer diagnosis. At the beginning of the study, 1,893 women completed a self-administered food-frequency questionnaire, and 1,513 of these women completed a follow-up questionnaire six years later. They were followed for 12 years on average following study entry.
The women were asked how often they consumed dairy foods during the previous year; what portion sizes they generally consumed; which products they ate, including milk, cheese, dairy desserts, yogurt and beverages made with milk (such as hot chocolate or lattes); and whether the dairy products were full fat, low fat or nonfat.
Of the total sample, 349 women had a recurrence of breast cancer and 372 died of any cause, 189 (50.8 percent) of them from breast cancer.
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