Pregnancy and Lactation Affect Markers of Calcium and Bone Metabolism Differently in Adolescent and Adult Women with Low Calcium Intakes

Abstract

Physiologic adaptation to the high calcium demand during pregnancy and lactation may be different in adolescents than in adults, particularly at low calcium intake. The aim of this cross-sectional study was to compare biochemical markers of calcium and bone metabolism between adolescent (14-19 y) and adult (21-35 y) women with calcium intake approximately 500 mg/d, in three different physiologic states, i.e., control (nonpregnant, nonlactating; NPNL), pregnant and lactating. Markers of calcium metabolism [serum Ca, P and intact parathyroid hormone (iPTH); urinary Ca and P] and of bone turnover [urinary deoxypyridinoline (D-Pyr) and plasma bone alkaline phosphatase (BAP)] were measured in NPNL (adolescents, n = 12 and adults, n = 25), pregnant (adolescents, n = 30 and adults, n = 36) and lactating (adolescents, n = 19 and adults, n = 26) women. In the NPNL women, iPTH, D-Pyr and BAP were higher (P < 0.001) and urinary Ca was lower (P < 0.001) in adolescents than in adults. Serum iPTH was higher (P < 0.001) and urinary Ca was lower (P < 0.01) in adolescents than in adults also in pregnancy and lactation. Compared with NPNL women, serum Ca decreased (P < 0.001) with pregnancy in adolescents but not in adults. The increase in D-Pyr with pregnancy and lactation was very pronounced in adults ( approximately 130%, P < 0.001) but less in adolescents (<25%, P < 0.01). BAP increased (P < 0.001) with pregnancy and lactation in adults ( approximately 60%) but decreased (P < 0.001) with pregnancy in adolescents ( approximately 13%). Pregnancy and lactation appear to affect bone turnover in adolescent and adult women with low calcium intake differently.

Serum calcium and phosphate level in normal pregnant women

“…Serum inorganic phosphate level found to the almost similar during pregnancy in different trimester. The lower level of serum calcium at third trimester is in agreement with others [17][18][19][20][21] . It is argued that increased need to the growing fetus and at the same time dilution of the molecule owing to increased extracellular fluid may explain the lower level of calcium level in third trimester.…”

“…This is contrast to other investigators, who demonstrated lower phosphorus during pregnancy (17). It was hypothesized that serum phosphate level falls during pregnancy due to low intake, hypoalbuminemia and increase demand for fetal growth (17).…”

Effect of calcium plus vitamin D supplementation during pregnancy in Brazilian adolescent mothers: a randomized, placebo-controlled trial

“…Moreover, irrespective of supplementation, serum PTH increased from midpregnancy to lactation in the adolescent mothers. Serum PTH does not typically increase from pregnancy to lactation in adult women with an adequate calcium intake (17), but it was shown to be higher in lactation than during pregnancy in adult mothers accustomed to a low-calcium diet (18,33) and in adolescent mothers (23). Therefore, increased PTH during lactation may have a homeostatic bone role in adolescent mothers.…”

“…Compliance was controlled by counting the remaining capsules at each visit and by telephone reminders. The dose of 600 mg Ca/d was chosen to bring the total daily calcium intake close to 1300 mg/d (22), with consideration that Brazilian adolescent mothers habitually consume a low-calcium diet (w500 mg/d) (7,23). The dose of 200 IU vitamin D/d was chosen to provide the current Adequate Intake of vitamin D for pregnant adolescents at the time when our study recruitment started (September 2009) (22).…”

Correlation between vitamin D3 deficiency and insulin resistance in pregnancy

“…The mechanism underlying the increased serum 1,25(OH)2D concentrations during pregnancy is not clear. PTH, which is usually considered the stimulus for increased renal hydroxylation of 25(OH)D to 1,25(OH)2D, has not been shown to increase during pregnancy [8][9][10].…”