Nutrition

Soy and Puberty: No Adverse Effect

By August 3, 2017 No Comments
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Throughout much of the world puberty is occurring at younger and younger ages. In particular, breast development and menarche in girls is occurring earlier.1 This trend toward earlier development most likely has a number of causes.

Exposure to hormonally-active agents in the environment has been proposed as one factor.1 So has the increase in body mass index (BMI) that is seen in many of these populations.2 Researchers are also looking at dietary factors. Not surprisingly, since they are a uniquely-rich sources of isoflavones, soyfoods have come under scrutiny as one possible factor in early puberty.

It’s not an easy relationship to study, though. Clinical trials aren’t realistically possible since they would require feeding soyfoods to hundreds of children for as long as five years. Epidemiologic studies in western countries also typically have limited value since soyfood intake is generally so low in these populations.

One exception, though, is the Seventh-day Adventist population. Approximately 40% of Adventists are vegetarian and soyfood intake is common among this group in general.  Two recently conducted retrospective studies involving Adventists have examined the impact of soy intake on puberty onset.

One of these studies included 248 boys aged 12–18 years attending schools near Adventist universities in Southern California and Michigan.3 It assessed the relationship of isoflavone intake to self-reported pubarche, which is development of pubic hair. Intake of soy isoflavones was assessed using a validated Web-based food frequency questionnaire.  Intake levels (mg/d) were designated as low (<3), moderate (3-20) and high (>20). Participants were asked to recall the age at which they first observed the growth of pubic hair around their genitals and other secondary sexual characteristics, such as growth of hair on the upper lip, chin, or side of face.

The results indicated that moderate and high total soy isoflavone intakes were significantly associated with earlier adjusted median age at pubarche: 12.58 years (relative risk [RR] + 95% confidence interval [CI]: 1.58 (1.06, 2.36)] for moderate consumers and 12.50 years [RR (95% CI): 1.63 (1.03, 2.60)] for high-consumers versus 13.00 years for low-consumers (reference group).  In contrast, there was no relationship between isoflavone intake and the development of facial hair.

It is clear from the results that there was no dose response between pubarche and isoflavone intake.  Median isoflavone intake in the moderate group was approximately 10 mg/d, which is the equivalent of less than ½ serving of a traditional Asian soyfood. It would be reasonable to expect that those in the high intake group, with a median intake of 54 mg/d (the amount in about two servings of soyfoods) would have experienced pubarche at younger ages if the relationship between isoflavones and pubarche holds true.  That is, if a true causal relationship exists, it’s unlikely that a maximum effect would have been seen at the moderate isoflavone intake level. The absence of any relationship between isoflavone intake and facial hair development also brings into question whether there is a causal basis for the observed relationship between isoflavones and male puberty.

Finally, as the study authors noted, the age of pubarche (12.50 years) is well within the normal range for boys even in the high intake group.  In fact, the age of puberche in the low-intake group was actually fairly late by the standards of Western countries.4

The second study looked at the relationship of isoflavone intake to age of menarche in 339 Adventist girls aged 12-18 years.5 Soyfood intake ranged from none to approximately 24 servings per week. Average age of menarche among the four intake groups ranged from 12.4 to 12.6 years (and was 12.6 years in both the high and low intake groups) with no statistically significant differences among the groups.

Generally, the findings from the two most relevant studies indicate that soy intake, even when quite high, does not adversely effect onset of puberty in either boys or girls.

 

References

  1. Schoeters G, Den Hond E, Dhooge W, van Larebeke N, Leijs M. Endocrine disruptors and abnormalities of pubertal development. Basic Clin Pharmacol Toxicol. 2008;102:168-75.
  2. Buyken AE, Karaolis-Danckert N, Remer T. Association of prepubertal body composition in healthy girls and boys with the timing of early and late pubertal markers. Am J Clin Nutr. 2009;89:221-30.
  3. Segovia-Siapco G, Pribis P, Oda K, Sabate J. Soy isoflavone consumption and age at pubarche in adolescent males. Eur J Nutr. 2017.
  4. Herman-Giddens ME, Steffes J, Harris D, et al. Secondary sexual characteristics in boys: data from the Pediatric Research in Office Settings Network. Pediatrics. 2012;130:e1058-68.
  5. Segovia-Siapco G, Pribis P, Messina M, Oda K, Sabate J. Is soy intake related to age at onset of menarche? A cross-sectional study among adolescents with a wide range of soy food consumption. Nutrition journal. 2014;13:54.
Dr. Mark Messina

Author Dr. Mark Messina

PhD in Nutrition, Executive Director, Soy Nutrition Institute. Expert in soyfoods and isoflavones.

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