A new study published in Pediatrics measured the proportion of girls who had entered puberty by ages 7 and 8, and saw striking increases compared to data collected in 1997, only 13 years ago. This study of U.S. girls found that by age 7, 10.4% of Caucasian girls (5% in 1997), 23.4% of African-American girls (15% in 1997), and 14.9% of Hispanic girls had already entered puberty. By age 8 the percentages were 18.3%, 42.9%, and 30.9%.1
This is distressing information, since early maturation is a well-established risk factor for breast cancer later in life.2 Cumulative exposure to ovarian hormones is a major determinant of breast cancer risk, and entering puberty early results in increased cumulative hormone exposure in young women.3
As I discussed in my book Eat to Live, age at menarche has been consistently decreasing over the past 100 years.4 In the medical literature, the probable causes of this continuing trend are clear - excess body fat and excess consumption of animal products are contributing factors to the declining age of puberty.
Obesity is a factor that increases one's exposure to estrogen, and multiple studies have found associations between excess weight during childhood and early menarche.5 Soft drink consumption, which is a contributor to the increasing rates of childhood obesity, is also associated with early menarche.2 A new study supporting this evidence was also published online in Pediatrics this week, analyzing connections between early childhood weight and age at onset of puberty. These researchers found that increased weight and body mass index (BMI) even at the early ages of 0-20 months was associated with earlier puberty.6
Total animal protein and meat intake at ages 3 and 7 were positively associated with age at menarche in a recent British study. Girls with the highest meat intake at age 7 were 75% more likely to have begun menstruating by age 12 ½ than those in the lowest category of meat intake.7
Physicians and parents are concerned about the social implications of this trend toward earlier maturity - seven year old girls are most likely not emotionally equipped to handle the onset of puberty. Unfortunately, the consequences of this trend are not only emotional. Early in life, our bodies are much more susceptible to carcinogenic influences - childhood diets are the major cause of adult cancers. It is becoming increasingly clear that the Western diet of meat, cheese, and processed food is harming our children, but many parents unknowingly continue to feed their children these disease-promoting foods. As parents, we must be proactive - we want the best for our children, and as such we must feed them the best possible foods. We can help to slow our children's development by feeding them a diet based on natural plant foods, which will groom their taste buds to prefer healthy foods at a young age and provide them with significant protection against cancers and other chronic diseases as they grow into adulthood.
1. Biro FM, Galvez MP, Greenspan LC, et al. Pubertal Assessment Method and Baseline Characteristics in a Mixed Longitudinal Study of Girls. Pediatrics. Published online August 9, 2010
Puberty coming earlier for U.S. girls: study. Yahoo! Health. August 9, 2010
2. Vandeloo MJ, Bruckers LM, Janssens JP. Effects of lifestyle on the onset of puberty as determinant for breast cancer. Eur J Cancer Prev. 2007 Feb;16(1):17-25.
Leung AW et al. Evidence for a programming effect of early menarche on the rise of breast cancer incidence in Hong Kong. Cancer Detect Prev. 2008;32(2):156-61.
3. Pike MC, Pearce CL, Wu AH. Prevention of cancers of the breast, endometrium and ovary. Oncogene. 2004 Aug 23;23(38):6379-91.
Bernstein L. Epidemiology of endocrine-related risk factors for breast cancer. J Mammary Gland Biol Neoplasia. 2002 Jan;7(1):3-15.
Key T, Appleby P, Barnes I, et al. Endogenous sex hormones and breast cancer in postmenopausal women: reanalysis of nine prospective studies. J Natl Cancer Inst. 2002;94:606-16.
Eliassen AH, Missmer SA, Tworoger SS, et al. Endogenous steroid hormone concentrations and risk of breast cancer among premenopausal women. J Natl Cancer Inst. 2006;98:1406-15.
4. Tanner JM. Trend toward earlier menarche in London, Oslo, Copenhagen, the Netherlands and Hungary. Nature 1973;243:75-76.
5. Mounir GM, El-Sayed NA, Mahdy NH, Khamis SE. Nutritional factors affecting the menarcheal state of adolescent school girls in Alexandria. J Egypt Public Health Assoc. 2007;82(3-4):239-60.
Britton JA, Wolff MS, Lapinski R, et al. Characteristics of pubertal development in a multi-ethnic population of nine-year-old girls. Ann Epidemiol. 2004 Mar;14(3):179-87.
6. Maisonet M, Christensen KY, Rubin C, et al. Role of Prenatal Characteristics and Early Growth on Pubertal Attainment of British Girls. Pediatrics. Published online August 9, 2010
7. Rogers IS, Northstone K, Dunger DB, et al. Diet throughout childhood and age at menarche in a contemporary cohort of British girls. Public Health Nutr. 2010 Jun 8:1-12.