A study by Segovia-Siapco
et al. published this year examined if in male teenagers who
consume more soya foods than the average American/European there is a
connection between soya isoflavone intake and the age at pubarche.
“Pubarche” means the age at which pubic hair first appears.
Soya
isoflavones (also called isoflavonoids) are a type of polyphenol in soya and
they can dock to estrogen receptors (ER) in the body. Both males and females
have these receptors. At the ER they can either have a pro-estrogenic effect or
an anti-estrogenic effect, or no effect.
High
soya consumers had the age of pubarche half a year earlier than
low consumers. There was no association of isoflavones with
first appearance of facial hair.
Summary:
- male teenagers 12 to 18 years
old (n = 248) who attended schools around Seventh Day Adventist universities in
Southern California and Michigan
- About 20% of the participants
were vegetarians.
- Moderate and high soy consumers had significantly higher proportions
of vegetarians.
- self-reported their age at
pubarche
- “Participants were asked to recall the age when they first observed
growth of pubic hair around their genitals and other secondary sexual
characteristics, such as growth of hair on upper lip, chin, or side of face.”
- intake of soy isoflavones was assessed using a validated Web-based
food frequency questionnaire
- The teenagers in this study consumed ~1–55 mg of isoflavones per day.
- Soya food intake from “dairy and meat alternatives in the school
cafeterias and at home” and possibly other soya foods.
- The study found that those male teenagers who consumed moderate to high amounts of soya foods and
therefore soya isoflavones had an
earlier age of pubarche than those who ate low amounts of soya foods.
- adjusted median age at pubarche low (<3 mg/d) isoflavone consumers: 13.0 years
- adjusted median age at pubarche moderate (3–20 mg/d) isoflavone
consumers: 12.6 years
- adjusted median age at pubarche high (>20 mg/d) isoflavone consumers: 12.5 years
- For all three groups age at pubarche is within the normal reported range for boys’
pubarcheal age.
- No significant association was
found between isoflavone intake and first appearance of facial hair.
- “Although timing is very variable for both facial and axillary hair
growth, it is estimated that facial hair in boys grows at about the same time
as axillary hair, which usually appears about 2 years after pubic hair first
occurs” [a very broad generalization, surely]
- “Pubertal timing is thought to be the outcome of the interaction
between genetic, endocrine, and environmental factors.” (Segovia-Siapco et al.
2017)
What is a “normal”
age at pubarche for boys?
- ages at pubarche reported from NHANES
III (USA): 12.0 years for whites, 11.2
years for African-Americans, and 12.3
years for Mexican-Americans (Segovia-Siapco et al. 2017)
- age at pubarche from a large study in China (18,807 urban Chinese boys; Ma et al. 2011): 12.78
years (Ma et al. 2011)
– “a population that is known to be highly exposed to soy” (Segovia-Siapco et
al. 2017)
- age at pubarche from earlier cross-sectional studies in Sweden and Iceland: ~12.7 years – These boys were probably
not eating a lot of soya foods. (Segovia-Siapco et al. 2017)
- “Marshall and Tanner [in 1970] approximated the mean (SD) age at
pubarche at 13.44 (1.09) but
cautioned about possible underestimation of pubarche in boys, since pubic hair
appearance may not be readily seen.” (Segovia-Siapco et al. 2017)
What other studies have shown (regarding
male sexual development/health and soya intake):
Effects of soya foods on puberty in males:
- The study presented above (Segovia-Siapco et al. 2017) is the only
study the potential effects soya intake in the age at pubarche.
- A prospective study from Germany
found no association between dietary
soya isoflavones and age at the
beginning of puberty or other pubertal
markers in 108 Caucasian German boys (age: ~ 9 years). The pubertal markers examined were initiation of gonadal growth (“Tanner
stage 2”, penis size [probably not measured] and testicle size, “testis volume
is determined by palpation using the Prader orchidometer. We have used age at
testis volume ≥4 mL to define the onset of gonadal development in boys”) and voice break. But these boys only
consumed 0–3 mg/d of soya
isoflavones (Cheng et
al. 2010).
Effects of soya
foods/soya isoflavone supplements on testosterone and other sex hormone levels
in male children:
-
There is one
epidemiologic study on this:
In a cross-sectional study in Japan (Aichi Province, 2006) with 230 boys (age: 3–6 years) soya intake and soya isoflavone intake
was associated with lower urinary
estrone and estradiol in boys. The
high isoflavone consumers in this group of boys consumed ~ 27 mg/d. The median intakes in all boys were from 5–27 mg/d (Wada et al. 2011).
“The clinical implications of the findings from this study, if any, are
unclear.” (Messina et al. 2017)
-
There is one clinical study on this:
In an 8-week crossover study in Israel that included
4 (!) boys (age: somewhere between 5.3 and 11.2 years) who suffered from high
cholesterol levels the boys received placebo or 16 mg or 48 mg/d of isoflavones
(supplement). This study showed no effects on serum levels of testosterone, FSH
(follicle stimulating hormone) or LH (luteinizing hormone) (Zung et al. 2010).
Effects of soya
foods/soya isoflavone supplements on testosterone and other sex hormone levels
in adult men:
The existing studies show no effect on circulating testosterone (Hamilton-Reeves et al. 2010)
or estrogen (Messina 2010) levels in
men.
Effects of soya foods/soya
isoflavone supplements on HDL cholesterol in male teenagers:
- A 6-week study in Australia tested
if soya isoflavones (50 mg/d) could increase HDL cholesterol (“good
cholesterol”) male teenagers (age:
16–18 y).
HDL levels are lower in men than in women, and HDL levels decrease as boys
enter puberty. The reason for this is probably related to testosterone or other
sex hormones.
The isoflavones in this study had no
effect on HDL levels (Dwyer
et al. 2008)
Effects of soya
infant formula sexual development in boys:
Studies with people men who were fed soya formula instead of receiving
breast milk have shown:
- In men there is no association
between being fed soya formula as an
infant with the following reproductive
health parameters: adult height, usual weight, education level, pubertal
maturation (age at first ejaculation, age when voice changed, age when hair
began to grow on chest, face, or pubic area) and pregnancy outcomes in sexual
partners impregnated by the male study subjects. Other outcomes, such as congenital
malformations in the men’s children, hormonal disorders, testicular cancer in
men, and homosexual orientation, were included as secondary outcomes but were
not expected to provide definitive results because these events were expected
to occur too infrequently.
This study included: 120 males receiving soya infant formula compared to
295 males receiving cow’s milk formula; study from 1999; men’s age: 20–34 years.
They had participated during 1965–1978 in controlled feeding studies conducted
at the University of Iowa, Iowa City (USA).
The soya infant formula didn’t turn them into vegans either: 0 of the
120 soya formula fed males were vegans as adults, whereas 4 out of 294 cow’s
milk formula fed males were vegans. (Strom et al., 2001)
- No association of between
being fed soya formula as an infant
and reproductive organ volumes –
breast bud volume, prostate volume, testicle volume – and testicle position (in the scrotum or undescended) at age 5.
This study compared 32 boys who
were breastfed with 28 boys who were
fed cow’s milk formula and 38 boys
who were fed soya formula. None of the soya formula fed boys had
undescended testicles while one boy of each the cow’s milk and the breast milk group
had undescended testicles – of course this was not statistically significant
and probably due to chance.
The boys in this study took part in the Beginnings Study in Central
Arkansas (USA); study period: 2010–2014 (Andres et al. 2015).
For comparison
|
|
Food
|
Soya isoflavone content
|
500 ml of soya milk
|
~ 50 mg
|
200 g of tofu
|
~ 50 mg
|
100 g natto
|
~ 60 mg
|
200 g tempeh
|
~ 90 mg
|
Average intake (adults) in some
East Asian countries & the US
|
Soya isoflavone intake
|
Japan
|
~ 25–50 mg/d
|
Shanghai
|
~ 40 mg/d
|
other areas of China
|
~ 10–80 mg/d
|
South Korea
|
~ 20 mg/d
|
high soya consumers in some East
Asian countries (estimate)
|
~ 100 mg/d
|
USA
|
~ 2 mg/d
|
Bai et al.
2014, Messina et al. 2006
|
|
Average intake (children/teenagers)
in some East Asian countries
|
Soya isoflavone intake
|
Japan, age: 1–14 y
|
~ 10–20 mg/d
|
South Korea, age: 2–18
y
|
~ 5–30 mg/d
|
China, age: 1–14 y
|
~ 10–40 mg/d
|
Messina
et al. 2017
|
|
Conclusion:
Based on this little evidence really nothing can be concluded - based on scientific evidence. There is no evidence that soya causes any harm to male teenagers, or other human males. One of the first things to think of when discussing "earlier puberty" is cancer risk. Nothing indicates that soya could raise male specific cancer risk - prostate cancer, testicular cancer, penis cancer, male breast cancer - in any age group.
My personal opinion is that there is nothing to worry about for boys and men regarding soya.
Prostate cancer is one of the most common cancers in men and surely I would love to see more human studies on soya foods and prostate cancer and other male sex specific issues. I would like to see such research because I am egocentric, male, and eat quite a lot of soya, and have a nerdy interest in the issue - but also because men's health and soya are relevant public health issues.
References
Andres A et al.: Compared with feeding infants breast milk or cow-milk
formula, soy formula feeding does not affect subsequent reproductive organ size
at 5 years of age. J Nutr. 2015 May;145(5):871-5. doi:
10.3945/jn.114.206201 . Epub 2015 Mar 11.
Bai
W, Wang C, Ren C: Intakes of total and individual flavonoids by US adults. Int
J Food Sci Nutr. 2014, 65: 9–20
Cheng G, Remer T, Prinz-Langenohl R, Blaszkewicz M, Degen GH, Buyken AE:
Relation of isoflavones and fiber intake in childhood to the timing of puberty.
Am J Clin Nutr. 2010 Sep;92(3):556-64. doi: 10.3945/ajcn.2010.29394 .
Epub 2010 Jul 14.
Dwyer T, Hynes KL, Fryer JL, Blizzard CL, Dalais FS: he lack of effect
of isoflavones on high-density lipoprotein cholesterol concentrations in
adolescent boys: a 6-week randomised trial. Public Health Nutr. 2008
Sep;11(9):955-62. Epub 2007 Sep 4.
Hamilton-Reeves JM, Vazquez G, Duval SJ, Phipps WR, Kurzer MS,
Messina MJ: Clinical studies show no effects of soy protein or
isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil
Steril. 2010 Aug;94(3):997-1007. doi: 10.1016/j.fertnstert.2009.04.038.
Epub 2009 Jun 12.
Ma HM et al.: Pubertal development timing in urban Chinese boys. Int J
Androl. 2011 Oct;34(5 Pt 2):e435-45. doi:
10.1111/j.1365-2605.2011.01173.x . Epub 2011 Jun 9.
Messina M: Soybean isoflavone exposure does not have feminizing
effects on men: a critical examination of the clinical evidence. Fertil
Steril. 2010 May 1;93(7):2095-104. doi: 10.1016/j.fertnstert.2010.03.002.
Epub 2010 Apr 8.
Messina
M, Nagata C, Wu AH: Estimated Asian adult soy protein and isoflavone intakes.
Nutrition and Cancer. 2006, 55 (1): 1–12
Messina M, Rogero MM, Fisberg M, Waitzberg D: Health
impact of childhood and
adolescent soy consumption. Nutr Rev. 2017 Jul
1;75(7):500-515. doi: 10.1093/nutrit/nux016
Segovia-Siapco
G, Pribis P, Oda K, Sabaté J: Soy isoflavone consumption and age
at pubarche in adolescent males. Eur J Nutr. 2017 Jul 15.
doi: 10.1007/s00394-017-1504-1 . [Epub ahead of print]
Strom BL et al: Exposure to soy-based formula in infancy and
endocrinological and reproductive outcomes in young adulthood. JAMA. 2001
Aug 15;286(7):807-14.
Wada K, Nakamura K, Masue T, Sahashi Y, Ando K, Nagata C: Soy intake and
urinary sex hormone levels in preschool Japanese children. Am J
Epidemiol. 2011 May 1;173(9):998-1003. doi: 10.1093/aje/kwr006 . Epub
2011 Mar 22.
Zung A, Shachar S, Zadik Z, Kerem Z: Soy-derived isoflavones treatment
in children with hypercholesterolemia: a pilot study. J Pediatr
Endocrinol Metab. 2010 Jan-Feb;23(1-2):133-41.