Role of calcium intake in modulating age-related increases in parathyroid function and bone resorption.
Serum parathyroid hormone (PTH) and bone resorption increase in elderly women and contribute to age-related bone loss. Whether these abnormalities are caused by calcium deficiency resulting from age-related decreases in absorption and renal conservation is unclear. We studied 28 normal elderly women (mean +/- SD, age 69.3 +/- 2.7 yr) who were maintained for 3 yr on usual calcium intake levels (20.4 +/- 7.2 mmol/day [815 +/- 289 mg/day]; n = 15) (known as the usual calcium group) or high calcium intake levels (60.4 +/- 6.5 mmol/day [2414+/260 mg/day]; n = 13) (known as the high calcium group) and a reference group of 12 normal young adult women (age 30.1 +/- 4.4 yr), whose calcium intake was 23.0 +/- 4.8 mmol/day (918 +/- 193 mg/day) (known as the young group). Serum PTH was measured every 2 h, and urinary excretion of deoxypyridinoline (Dpd), a new marker for bone resorption, was measured in 4 h collections. Parathyroid gland secretory capacity was assessed during induced hypocalcemia. The mean 24 h serum PTH was 40% lower (P < 0.001), and the mean 24 h urinary Dpd was 35% lower (P < 0.005) in the high than in the usual calcium group. Mean parathyroid gland secretory capacity also was 47% lower (P < 0.005) in the high calcium group than in the usual calcium group. However, the usual calcium group had a mean 24 h serum PTH level that was 70% higher (P < 0.001) and a mean 24 h urinary Dpd level that was 30% higher (P < 0.005) than the young group, whereas the high calcium group was indistinguishable from the young group. Thus, failure of elderly women to increase their calcium intake to offset age-related increases in calcium requirement contributes substantially to their development of increased parathyroid activity and increased bone resorption, whereas a high calcium intake can reverse both abnormalities.
McKane
W R
WR
Division of Endocrinology and Metabolism, Mayo Clinic, Rochester, Minnesota 55905, USA.
Khosla
S
S
Egan
K S
KS
Robins
S P
SP
Burritt
M F
MF
Riggs
B L
BL
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000596:Amino Acids / Q000652:urine; D001862:Bone Resorption; D002118:Calcium / Q000008:administration & dosage* / Q000097:blood; D002940:Circadian Rhythm; D004032:Diet; D005260:Female; D006801:Humans; D010280:Parathyroid Glands / Q000502:physiology*; D010281:Parathyroid Hormone / Q000097:blood
D000596:Amino Acids; D010281:Parathyroid Hormone; C036020:deoxypyridinoline; D002118:Calcium