Background/aims. Steroids influence bone mineral but there is little data of their effect in the newborn. This study aimed to measure the effects of dexamethasone, used in bronchopulmonary dysplasia (BPD), on bone mineralisation and on calcium and phosphorus balance.

Subjects. Infants <1500g birthweight with BPD, divided into those given steroids (“steroid”, n=16) and those not treated(“controls”, n=12).

Methods. All had two 3 day mineral balances: during the second week, before start of any steroids, and at 8-10 weeks of age. The steroid group had an extra balance during the first week of treatment. Weekly measurements were made of bone mineral content (BMC) and of plasma calcium, phosphate, and 1,25 dihydroxycholecalciferol (1,25 diOHD).

Results. The BMC was similar in both groups until 9 weeks of age, when the rate of accretion was then slower in the steroid group (0.05 vs 0.13 mg/mm/week, p=0.001). Steroids caused a fall in calcium absorption (62.5% to 44.7%, p<0.001), calcium retention (55.9% to 40.9%, p=0.002) and phosphate retention (56.4% to 39.5%, p=0.02). Calcium absorption (60.9% vs 70.4%, p=0.01) and retention (58.2% vs 67.7%, p=0.01) remained lower after the end of treatment compared with the controls. In the steroid group plasma calcium, phosphate and 1,25 diOHD fell during the first 4 weeks and were significantly lower than in the control group.

Conclusions. This confirms that steroids reduce absorption of calcium, probably by an effect on vitamin D, and reduce mineral retention. An effect on plasma calcium and phosphate was seen and, although in the short term no difference was shown in BMC, later mineralisation was reduced in the steroid group, possibly due to persisting poorer mineral absorption and retention.