Urinary hormone levels during the natural menstrual cycle: the effect of age

A number of studies have identified hormonal changes in women during their reproductive lifespan, many focusing upon changes in women over the age of 40 years. The present study has determined the effect of increasing age on hormone levels over three decades. Daily early morning urine samples were assayed for estrone-3-glucuronide (E3 G), pregnanediol-3-glucuronide (P3 G), testosterone-17-glucuronide (T17 G), FSH and LH. An examination of the validity of using creatinine as a volume adjuster in urine samples formed an integral part of the analysis. Volunteers were healthy women who had regular (25-35 days) cycles, were not taking oral contraceptives, hormone therapies or any other medication. Three age groups were compared: 20-29 years (n=13), 30-39 years (n=9) and 40-49 years (n=13). Statistical analyses were carried out using two-way ANOVA and post hoc t-tests. Creatinine excretion, despite revealing no cycle-related variation in any age group, showed a decline with increasing age. Creatinine output was significantly lower in the 40-49 years age group in all phases of the cycle than in the 20-29 and 30-39 groups (P<0.0001). Uncorrected levels of E3 G were significantly higher in the 30-39 years group when compared with the 40-49 age group (P<0.0001). Uncorrected P3 G output was significantly higher in women aged 20-29 years than in women aged 40-49 years (P<0.001) and levels of uncorrected T17 G were higher in the 20-29 year age group when compared with the 30-39 or 40-49 years age group (P<0.0001). The present study is consistent with previous reports that have revealed a decline in creatinine clearance with increasing age, and therefore casts into some doubt the validity of using creatinine clearance as a procedure to correct for volume fluctuations in differing age groups of women. The study also demonstrates unequivocally that age-related variations in hormone levels are not restricted to women over 40 years of age. The novel finding of highly significant differences in mean levels of T17 G between the age groups is of considerable interest. It is presently unclear whether this resulted from specifically increased ovarian and/or adrenal secretion. The possible impacts of changes in testosterone levels during the female reproductive lifespan merits further study.