Inorganic sulfate is a physiological anion which is utilized in the me
tabolism of both endogenous compounds and xenobiotics. Its homeostasis
is maintained predominantly by facilitated reabsorptive processes in
the kidneys. The objectives of the present investigation were to evalu
ate the effects of menopausal status and caffeine ingestion on the ser
um concentrations and clearance of inorganic sulfate. Thirty-nine wome
n who were classified as premenopausal, postmenopausal with or without
estrogen treatment, and postmenopausal with osteoporosis participated
in the study. The women were studied on two separate occasions follow
ing the ingestion of a decaffeinated beverage to which 6 mg caffeine/k
g lean body mass or no caffeine was added. All women were habitual caf
feine users (mean ingestion of 588 mg caffeine per day) but abstained
from all caffeine sources for 2 weeks prior to the control study day.
Postmenopausal women with estrogen supplementation exhibited significa
ntly lower sulfate serum concentrations (0.24 +/- 0.02 mM vs. 0.32 +/-
0.04 mM in premenopausal women, mean +/- SD, p<0.05) and a decreased
renal reabsorption of sulfate for the control (no caffeine) period. Th
ere was no difference in serum sulfate or sulfate reabsorption in estr
ogen supplemented postmenopausal women, compared with women not taking
estrogen. Postmenopausal women with osteoporosis had significantly lo
wer creatinine and sulfate clearances than postmenopausal women with e
strogen supplementation which may be related to their older age, or fa
ctors related to the disease process. The 6 mg/kg dose of caffeine cau
sed a diuresis, but no change in GFR, as indicated by urine volume and
creatinine clearance values, respectively. Caffeine administration re
sulted in an increase in the sulfate excretion rate; there was no chan
ge in sulfate serum concentrations. The results of this investigation
indicate that menopause results in decreased sulfate serum concentrati
ons that may be the consequence of a decreased renal reabsorption of s
ulfate. Secondly, this investigation demonstrated that caffeine ingest
ion increases the urinary excretion of sulfate, an effect that may be
related to the diuretic effect of caffeine or due to a caffeine-induce
d alteration in the renal reabsorption of sulfate.