Urine calcium and urine sodium concentrations are not related, after adjustment for urine magnesium.
OBJECTIVE
Urine calcium correlates with urine sodium. The aims of this study were to investigate whether the urine sodium-calcium relationship persists into old age and whether it holds after adjustment for urine magnesium.


METHODS
Cross-sectional descriptive analysis.


METHODS
Residents of two aged care institutions (median age 84 years) who were not taking diuretics, calcium or vitamin D supplements.


METHODS
Early morning urine calcium, sodium and magnesium, plasma creatinine and serum 25-hydroxyvitamin D and parathyroid hormone.


RESULTS
Urine calcium correlated with urine sodium (r = 0.29, P < 0.01) and with urine magnesium (r = 0.56, P < 0.001). After adjustment for urine magnesium, the relationship between urine sodium and urine calcium was no longer significant. Forty-five percent of the interindividual variation in urine calcium was explained by a linear model on the basis of urine magnesium and plasma creatinine.


CONCLUSIONS
The data indicate that a correlation between urine sodium and calcium persists in very old age. However, this correlation no longer holds after adjustment for urine magnesium. Further studies examining urine calcium excretion should also consider urine magnesium.
University of Melbourne, Department of Medicine, The Royal Melbourne Hospital, Victoria, Australia.
M S
MS
Stein
L
L
Flicker
S C
SC
Scherer
K E
KE
Mead
S L
SL
Walton
P
P
Chick
M
M
Di Carlantonio
J D
JD
Zajac
J D
JD
Wark
D015652:25-Hydroxyvitamin D 2 / Q000097:blood; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood / Q000652:urine*; D002118:Calcium / Q000652:urine*; D003404:Creatinine / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D016014:Linear Models; D008274:Magnesium / Q000652:urine*; D008297:Male; D010281:Parathyroid Hormone / Q000032:analysis; D012964:Sodium / Q000652:urine*
D010281:Parathyroid Hormone; D015652:25-Hydroxyvitamin D 2; D012964:Sodium; D003404:Creatinine; D008274:Magnesium; D002118:Calcium