The authors write:
Not considering different genetic backgrounds (genotpye) ...
"Sex-related hormone measures of testosterone (total T, bioavailable-T, and free-T) and sex hormone binding globulin (SHBG) were not significant in the combined nor sex-stratified effects estimation (S4 Fig).""[.] without considering genetic differences, we replicated previous findings [46 [EPIC-Oxford study]] that vegetarianism does not have significant effects on the cholesterol-derived sterol hormone testosterone (total T, bioavailable-T, and free-T), nor on the testosterone inhibitor SHBG, in both full [both men and women combined] and sex-stratified [men and women separately] models."
Considering different genetic backgrounds (genotype) ...
"A genotype-stratified model indicated vegetarianism is associated with a 0.039-unit decrease in testosterone ([-0.068, -0.010]; P = 0.009) in TT individuals, but with a 0.175-unit increase ([0.100, 0.249]; P = 4.44×10−6) in TC individuals (Fig 4C)." But this effect is for both men and women combined (see figure 4C). If understand correctly, a "0.039-unit decrease" means a 0.039 nmol/L decrease, i.e., in this case a decrease of less than 1% (see supplementary table "S2", even though the exact data are not given).Figure 4C (men and women combined):
Figure S12 (men and women separately):
Comment:
The vertical lines crossing the horizontal line in the middle indicate a statistically non-significant effect, i.e., the effect was significant only for TC (small increase) in men and TT (small decrease) in women. While the absolute change shown here seems larger in TC men than in TT women, one needs to take into account that absolut testosterone blood levels are much higher in men. Therefore, the relative effect shown here is larger in TT women than in TC men. Assuming a typical testosterone level of around 20 nmol/L in the male group [as shown in the EPIC-Oxford study], the increase seen here in TC men is an increase of about 1%, i.e., a very small and likely irrelevant change. Assuming typical testosterone blood levels in women in the range of 0.6 to 1.2 nmol/L [Davis & Tran 2001], the decrease seen here in TT women of about 0.08 (I'm guessing based on figure S12) nmol/L would be a decrease of about 10%. Based on my understanding this is still a small and probably insignificant change.
Healthy lifestyle changes (diet and/or exercise) typically cause a beneficial, small testosterone decrease in women, with an effect of about -0.1 to -0,2 nmol/L [Haqq et al. 2014], which is similar to the ~0.08 nmol/L decrease in the study discussed here (figure S12).