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Intestinal calcium absorption in men with spinal osteoporosis
A G Need1, H A Morris, M Horowitz
1Division of Clinical Biochemistry, Institute of Medical and Veterinary Science, Adelaide, South Australia.
Objective:
To investigate the role of serum 1,25-dihydroxyvitamin D (1,25D) in the decreased calcium absorption found in men with osteoporosis.
Design:
Prospective study of patients referred to a university teaching hospital clinic for investigation of possible osteoporosis.
Patients:
Male patients referred for investigation for osteoporosis, from 1981 to 1995, because of specific risk factors or radiological suspicion of osteoporosis. Men with vertebral compression fractures were compared with those without.
Measurements:
Height and weight, radiocalcium absorption, serum 1,25D and fasting urinary calcium and hydroxyproline excretion.
Results:
The men with vertebral fractures had higher fasting urinary hydroxyproline excretion (P = 0.003) and lower calcium absorption (P = 0.002) than the men without. Calcium absorption was positively related to 1,25D in both groups but the estimated calcium absorption at zero 1,25D was lower in the osteoporotic than the normal group. 1,25D was lower in the osteoporotic group than in the normal group. However this difference could only explain about half of the difference in calcium absorption between the groups.
Conclusions:
Calcium absorption is low in men with osteoporosis. About half of the deficit is due to low serum 1,25-dihydroxy vitamin D levels but there appears, in addition, to be some intestinal resistance to its effect on calcium absorption.