Patients who consume high-fat dairy products following breast cancer diagnosis increase their chances 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," wrote lead author Candyce H. Kroenke, ScD, MPH, staff scientist with the Kaiser Permanente Division of Research, and co-authors.
"Specifically, 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," said Kroenke. The category of high-fat dairy products researchers tracked 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.
"High-fat dairy is generally not recommended as part of a healthy diet," said senior author Bette J. Caan, DrPH, research scientist with the Kaiser Permanente Division of Research. "Switching to low-fat dairy is an easy thing to modify."
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.
This research was part of the Life After Cancer Epidemiology (LACE) study, one of several efforts by investigators with the Kaiser Permanente Division of Research to consider the role of lifestyle factors such as nutrition, exercise and social support on long-term breast cancer survival and recurrence. While hundreds of studies have examined the role of lifestyle factors in cancer risk and prevention, this study is one of a small but growing number that focus on the role of lifestyle factors after a breast cancer diagnosis.
For example, the Pathways study of breast cancer survivorship, based at the Division of Research, is collecting and analyzing data about women's genetic background, tumor characteristics and lifestyle choices immediately after diagnosis. Findings from this study, along with the LACE study, are providing objective information to help guide women as they make decisions following a breast cancer diagnosis; among these findings are that soy decreases the risk of breast cancer recurrence, quality of life after diagnosis influences outcomes, and physical activity is beneficial.
Susan E. Kutner, MD, chair of the Kaiser Permanente Northern California Regional Breast Care Task Force, said that the new study bolsters the counseling that Kaiser Permanente gives breast cancer survivors about the importance of a low-fat diet, as well as exercise and weight management, in preventing recurrence of the disease. "Women have been clamoring for this type of information," Kutner said. "They're asking us, 'Tell me what I should eat?' With this information, we can be more specific about recommending low-fat dairy products."