Soy and Childlessness
A report from Adventist Health Study-2 was recently released examining the association between soy intake (measured as isoflavones) and childlessness (1).
The authors write:
“The results suggest that when the isoflavone intake exceeds approximately 40 mg per day, the overall lifetime risk of never becoming pregnant increased by 13% and that of ever giving birth to a live child was reduced by approximately 3%. The associations were consistently found to be stronger in women who reported having had difficulties in becoming pregnant (1 straight year or more without success to become pregnant).”
40 mg of isoflavones per day is the equivalent of about 2 servings of soy per day.
There are some reasons not to conclude that soy causes childlessness:
• The author’s stated that, “One major limitation in our study is that we are not able to distinguish with certainty between involuntary and voluntary childlessness.”
• The finding for never becoming pregnant was 1.13 (1.02, 1.26) for women eating 40 mg of isoflavones per day compared to those eating only 10 mg. This is barely statistically significant.
• It was a cross-sectional study with relatively weak findings. Cross-sectional studies can indicate what should be studied prospectively and in clinical trials, but cannot prove causation.
• The researchers did a lot of testing with many different models, the results of which didn’t always agree. The authors stated in their discussion, “[G]iven the somewhat exploratory nature of our analyses and the many statistical tests conducted, we do not believe that [an inconsistency they found] deserves much emphasis at this point.” Indeed – that could apply to their main finding.
Despite the limitations, if someone is having a hard time becoming pregnant, cutting out the soy might be something to try.
The study is linked to in the reference below and is free to the public.
I have updated the VeganHealth.org article, Soy: What’s the Harm?
1. Jacobsen BK, Jaceldo-Siegl K, Knutsen SF, Fan J, Oda K, Fraser GE. Soy isoflavone intake and the likelihood of ever becoming a mother: the Adventist Health Study-2. Int J Womens Health. 2014 Apr 5;6:377-84. doi: 10.2147/IJWH.S57137. eCollection 2014. | link