Endogenous fecal losses of calcium compromise calcium balance in pancreatic-insufficient girls with cystic fibrosis

Objective: Bone mineral density is compromised in individuals with cystic fibrosis (CF); calcium is the major bone mineral. This study examined the impact of endogenous fecal calcium (V_endo) losses on calcium balance in girls with CF. Study design: V_endo was measured in 12 girls with CF (aged 7-18 years): 7 younger, premenarcheal girls with compromised nutritional status: and 5 older, postmenarcheal girls with adequate nutritional status. V_endo was measured as the amount of intravenously administered ⁴²Ca, a calcium stable isotope, in stool relative to urine over 6 days. V_endo was compared between pre- and postmenarcheal girls by Student's t test. Actual calcium balance [absorbed calcium-(urinary calcium (V_u) + V_endo)] was compared with estimated balance (assuming V_endo = 1.6 mg/kg/day calcium) by paired t test. Results: V_endo was 99.3 ± 42.3 mg/day. By body weight, V_endo was highest among premenarcheal girls (3.37 ± 1.09 mg/kg/day), resulting in excess losses (>1.6 mg/kg/day) of 55.0 ± 45. 7 mg/day. Over 1 year, this represents 20.1 ± 16.7 g of unattained bone calcium or 6.7 ± 4.2% of die bone calcium content of these girls. Conclusions: V_endo is a significant source of calcium loss in individuals with CF and may limit calcium availability for bone mineral deposition.