Interrelationship among vitamin D metabolism, true calcium absorption, parathyroid function, and age in women: evidence of an age-related intestinal resistance to 1,25-dihydroxyvitamin D action.
We studied the mechanism of impaired calcium absorption with aging in 51 healthy women whose ages ranged from 26 to 88 years. Serum concentrations of 1,25-dihydroxyvitamin D [1,25-(OH)2D, mean of four measurements per subject] increased with age by 22% (P less than 0.05) but, by split-point analysis, plateaued or decreased slightly after age 65. In a subset of 20 subjects, [3H]1,25-(OH)2D3 kinetic analysis showed that this increase with age resulted from both increased production and decreased metabolic clearance of 1,25-(OH)2D. Despite the increase in serum 1,25-(OH)2D concentration, true calcium absorption did not change with age. The expected inverse correlation between true fractional calcium absorption and dietary calcium intake, however, was easily demonstrated (r = 0.66, P less than 0.001). Serum intact parathyroid hormone (PTH) increased with age by 35% (P less than 0.02) and serum bone gla protein (BGP, osteocalcin) increased by 47% (P less than 0.001); the increases in serum PTH and serum BGP were directly correlated (r = 0.32, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Eastell
R
R
Endocrine Research Unit, Mayo Clinic, Rochester, MN 55905.
Yergey
A L
AL
Vieira
N E
NE
Cedel
S L
SL
Kumar
R
R
Riggs
B L
BL
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D015415:Biomarkers / Q000097:blood; D002117:Calcitriol / Q000378:metabolism* / Q000502:physiology; D002136:Calcium, Dietary / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D007408:Intestinal Absorption / Q000502:physiology*; D008875:Middle Aged; D015675:Osteocalcin / Q000097:blood; D010280:Parathyroid Glands / Q000502:physiology*; D010281:Parathyroid Hormone / Q000097:blood
D015415:Biomarkers; D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D015675:Osteocalcin; D002117:Calcitriol