It’s one of the most popular current misconceptions about milk: that it causes early-onset puberty in girls – known clinically as precocious puberty. This notion gained widespread exposure after the mid-1990s, when some animal-rights and anti-biotechnology advocates suggested a link between precocious puberty and consumption of milk from cows supplemented with recombinant bovine somatotropin (rbST – also known as “bovine growth hormone”). To those unarmed with the facts, such a suggestion had a certain plausibility: an animal growth-inducing hormone, ingested via cow’s milk, might promote accelerated growth rates in humans – and show itself in the form of early-onset puberty. It made for a scenario guaranteed to scare any responsible parent. But is any of it true? According to scientists who have examined the theory, no – it isn’t true. There is no conclusive evidence to support the suggestion that consumption of milk – whether derived from a rbST-supplemented cow or not -- causes early-onset puberty in girls. Although some studies suggest a decrease in the age of onset of puberty in recent decades (Kaplowitz, P. Curr. Opin. Obstet. Gynecol. 18: 487, 2006; and Kaplowitz, P. Pediatrics 121 (suppl 3): 208s, 2008), the causes behind this trend have not been confirmed. Among the possible culprits, socioeconomic conditions, psychological conditions (including stress), nutritional status, dietary quality, chronic diseases, birth weight and early postnatal growth have all been examined (Ellis, B.J., and M.J. Essex. Child Develop. 78: 1799, 2007; Semiz, S., F. Kurt, D.T. Kurt, et al. Turk. J. Pediatr. 51: 49, 2009; Karaolis-Danckert, N., A.E. Buyken, A. Sonntag, et al. Am. J. Clin. Nutr. 90: 1559, 2009; and Cheng, G., S. Gerlach, L. Libuda, et al. J. Nutr. 140: 95, 2010). Several studies link higher body mass index or increased body fatness in girls with earlier initiation or progression of puberty – and in fact, overweight and obesity have emerged as the favorite candidates for explaining precocious puberty among many scientists (Kaplowitz, P. Curr. Opin. Obstet. Gynecol. 18: 487, 2006; Kaplowitz, P.B. Pediatrics 121(suppl 3): 208s, 2008; Lee, J.M., D. Appugliese, N. Kaciroti, et al. Pediatrics 119: e624, 2007; DiVall, S.A., and S. Radovick. Curr. Opin. Endocrinol. Diabetes Obes. 16: 1, 2009; and Buyken, A.E., N. Karaolis-Danckert, and T. Remer. Am. J. Clin. Nutr. 89: 221, 2009). There’s a rationality about the theory that’s appealing. Many – probably too many – American girls carry more weight compared to previous generations and many have lifestyles that are sedentary compared to previous decades. Most enjoy access to high-quality food and medical care. The development of the human body responds to external stimuli. When it is well-fed, well-rested and disease-free, it will prioritize its next basic requirement: reproduction. It may well be that American girls are experiencing higher incidences of precocious puberty because we have built a society that encourages precocious puberty. Circumstantial evidence tends to let milk off the hook, as well. The studies cited above suggest that precocious puberty has been on the rise at the very same time that per capita consumption of dairy foods – especially by girls – has been in decline (Kaplowitz, P.B. Pediatrics 121(suppl 3): 208s, 2008; and Nielsen, S.J., and B.M. Popkin. Am. J. Prev. Med. 27: 205, 2004). Further, there has been little if any evidence to suggest that boys are maturing at faster rates – even though per capita consumption of dairy by boys is and has been significantly higher than that among girls. And what about rbST – which allegedly induces faster growth rates in human children? Bunk, says mainstream science. While all foods derived from animals contain minute traces of growth hormones, such hormones are species specific – that is, they only work on their own kind. Decades of tests on bovine growth hormone have confirmed that it is inactive in human biology (U.S. Food and Drug Administration. Report of the Food and Drug Administration’s Review of the Safety of Recombinant Bovine Somatotropin. April 23, 2009; please visit www.rbSTFacts.org). Only human somatotropin (hST or “human growth hormone”) is effective in stimulating growth in humans. So the next time someone tells you that milk causes early-onset puberty, do two things: first, continue to allow your children to drink milk (it’s full of nutrients they need); and then consider the source of the information you’re hearing.