DIURNAL-VARIATION OF BONE-MINERAL TURNOVER IN ELDERLY MEN AND WOMEN

The diurnal variation of markers of bone mineral metabolism have been documented in pre- and early postmenopausal women. Such rhythms have c linical implications for timing of sample collection and assessment of therapeutic intervention. To examine the diurnal variation of bone tu rnover in the elderly, we examined markers of bone formation [serum os teocalcin (OC) and bone-specific alkaline phosphatase (B-ALP)]; a mark er of bone resorption (urinary N-telopeptide cross-linked collagen typ e 1 [NTX]); and serum calcium and parathyroid hormone (PTH) over 24 ho urs. Subjects were healthy community-dwelling elderly who were on no m edications known to significantly alter bone mineral metabolism, Subje cts included 14 women [74 +/- 6 years (mean +/- SD)] and 14 men (80 +/ - 5 years). Over the 24-hour sampling period, mean serum OC, B-ALP, an d calcium values were similar in elderly men and women. However, mean serum PTH was significantly higher in elderly men compared with women (P < 0.05). The magnitude of the diurnal variation of urinary NTX was significantly higher in women compared with men (P < 0.05), There was a significant diurnal variation for serum OC, B-ALP, calcium, PTH, and urinary NTX in both elderly men and women, The magnitude of the diurn al variation was approximately 10-20% of mean value for OC and B-ALP, 30% for PTH, and up to 40% for urinary NTX. We conclude that there is significant diurnal variation in the markers of bone mineral metabolis m for elderly men and women. The peak value, which on average would be 20% higher than the mean value for urinary NTX, highlights the import ance of the timing of sample collection for appropriate interpretation of therapeutic response, In addition, gender-related differences, inc luding relatively higher levels of serum PTH and lower levels of urina ry NTX in elderly men, may help explain differences in rates of bone l oss in this age group.