Soyfoods are without effect on the age of onset of menarche
In many countries throughout the world, the age at which puberty occurs among girls—manifested as breast development, appearance of pubic hair, and onset of menarche—has been commencing earlier. For example, the mean age at onset of menarche (AOM) in Korea decreased from 16.9 to 13.8 years between 1920 and 1985. In the United Kingdom, between 1910 and 1993, it decreased from 13.5 to 12.3 years. And in the United States the AOM decreased by an average of 3 to 5½ months from 1960 to 1990.
These trends in pubertal development raise concerns because early onset of puberty may negatively influence the future health of adolescent girls. Most importantly in this regard, earlier menarche has been implicated in the etiology of breast and ovarian cancer; in fact, early menarche has been found to contribute more to breast cancer risk than early menopause. Therefore, the decline in the AOM may result in an increased incidence of hormone-related cancers.
A number of factors, such as body composition and body weight have been identified as influencing AOM. Dietary factors, such as animal protein and meat and milk and total dairy, have also been linked to pubertal timing. Hormonally-active agents, such as bisphenol-A, a chemical produced in large quantities for use primarily in the production of plastics, which is classified as an endocrine disruptor, has also been evaluated. Endocrine disruptors are chemicals that may interfere with the body’s endocrine (hormone) system and produce adverse developmental, reproductive, neurological, and immune effects. Because soyfoods are such rich sources of isoflavones, which are classified as phytoestrogens, there has been interest in understanding how these foods might affect the AOM.
Until recently, no study had evaluated the relationship between soyfood intake and AOM. But the existing evidence certainly didn’t suggest that soy would cause a decline in the AOM because as noted, earlier AOM is associated with an increased risk of breast cancer whereas there is substantial evidence indicating that consuming soy early in life is protective against this disease. In fact, population studies in the United States and China, suggest that risk can be reduced by as much as 50 percent by eating just one serving of soyfoods per day during adolescence. Nevertheless, because there is no substitute for actual data, researchers from Loma Linda University (LLU) decided to determine whether soy affects the AOM.
It is difficult to gain meaningful insight about soy and isoflavones from population studies conducted in Western countries because few people regularly eat soyfoods. However, the Seventh-day Adventist population, the group chosen by LLU researchers for their study, is very health-conscious and about 40% are vegetarians. Consequently, soy consumption is quite high among this group. In fact, more than 20% of the girls enrolled in this study consumed soyfoods at least 4 times per day and the mean number of servings per week was 12.9.
This cross-sectional study included a total of 327 girls; the age range was between 12 and 18 and the mean age was 15.0. Soy intake (categorized as total soy, meat alternatives, tofu/traditional soy, and soy beverages) as well as other pertinent characteristics of the participants was collected from a web-based dietary questionnaire and physical development tool while the AOM was self-reported.
The mean AOM was 12.5 years for the approximately 90% of the participants who had reached menarche. Consumption of total soyfoods and the three types of soyfoods examined were not significantly associated with the AOM nor was intake associated with the odds for early- or late-AOM. Adjustment for demographic and dietary factors did not change the results.
In conclusion, the results of this first of its kind study show that soy intake does not affect the age at which girls begin menstruation. These findings are certainly welcomed news because with all of the evidence linking early soy intake with a reduced risk of breast cancer, the consumption of soyfoods by girls is one dietary step that should be encouraged.
Segovia-Siapco G, Pribis P, Messina M, et al. Is soy intake related to age at onset of menarche? A cross-sectional study among adolescents with a wide range of soy food consumption. Nutr J. 13,54 (2014).