Drinking milk in teen years linked to increased prostate cancer risk
REYKJAVIK, ICELAND - According to a new study, milk intake during puberty, when the prostate gland is developing, may triple the risk of developing prostate cancer later in life. Researchers at the University of Iceland in Reykjavík published their findings online on December 20 in the American Journal of Epidemiology.
The study group was comprised of 8,894 men born between 1907 and 1935 in Iceland. The investigators reviewed cancer and mortality registers and followed the men for prostate cancer diagnosis and mortality from study entry (in waves from 1967 to 1987) through 2009. In 2002-2006, a subgroup of 2,268 men reported their milk intake in early, mid-, and current life. During an average follow-up period of 24.3 years, 1,123 men were diagnosed with prostate cancer, including 371 with advanced disease (stage 3 or higher or prostate cancer death). Location did not appear to be a significant factor. Compared with early-life residency in the capital area, rural residency in the first 20 years of life was marginally associated with increased risk of advanced prostate cancer, particularly among men born before 1920 Daily milk consumption in adolescence (vs. less than daily), but not in midlife or currently, was associated with a 3.2-fold risk of advanced prostate cancer. The authors concluded that their data suggested that frequent milk intake in adolescence increases risk of advanced prostate cancer.
Adolescence and prostate cancer
"We believe that our data are indeed solid and provide important evidence for the role of adolescence as a 'sensitive period' for prostate cancer development," noted Johanna Torfadottir, a nutrition scientist and a graduate student at the University of Iceland. She added, "However, we remain cautious in our interpretation. Causal inferences are not made on one study alone, thus more studies are needed to confirm our findings and also to explore possible mechanism behind this association." She also noted that two previous studies on prostate cancer and milk intake in adolescents arrived at mixed conclusions. One reported that milk drinkers appeared to be somewhat protected against the disease, while the other found no relationship at all. She added that but both studies were small and did not differentiate between advanced and early-stage tumors.
The researchers wrote that, in contrast to the two small studies, Iceland offers the perfect "natural experiment." The nation had minimal infrastructure during the early 20th Century; thus, residents of rural areas tended to live off the land. Individuals living in the central regions of the nation had a lifestyle that included the ingestion of large quantities of milk from farm animals. In contrast, milk was scarce in Iceland’s seaside villages.
The difference in the incidence of incidence among milk drinkers was not found to be related to how often the men visited a physician for a check-up, their education, or other foods they customarily ate, such as fish or meat. Furthermore, milk intake was not found to be linked to the men’s risk of early-stage tumors. Also, milk intake of middle-age men did not impact their prostate cancer risk.
Ms. Torfadottir noted that several physiological mechanisms have been proposed to explain the connection; however, they all are hypothetical. She noted, "From these data alone we cannot recommend that teenage boys should change their dietary habits. We are only looking at the risk of one disease, prostate cancer, and obviously risks of other conditions, e.g. bone health, need to be considered."
Take home message: All things considered, it would be prudent for teen age boys to avoid milk products. One must remember that milk is a food product designed for baby cows. All mammals produce a species-specific type of milk. Human milk is designed for human infants and has less fat content than cow’s milks. Many infant formulas are derived from cow’s milk; however, some infants develop allergies and must be switched to a different product. In addition, some children and adults are lactose intolerant. Beyond infancy, it is not necessary to consume milk products. Other sources of calcium are plentiful, such as calcium-fortified orange juice, calcium-fortified soy milk, or calcium tablets. One cup of whole milk contains 33 mg of cholesterol (both LDL (“bad cholesterol and HDL (“good” cholesterol).