Background Infants and young children might be particularly susceptible to the potential side effects from inhaled corticosteroid (ICS) on height and bone mineral content (BMC), but this has rarely been studied in long-term prospective studies.

Methods Children from two Copenhagen Prospective Studies on Asthma in Childhood cohorts were included. ICS use was registered prospectively from birth to age 6 and the cumulative dose was calculated. Primary outcomes were height and BMC from dual-energy X-ray absorptiometry (DXA) scans at age 6.

Results At age 6, a total of 930 children (84%) from the cohorts had a valid height measurement and 792 (71%) had a DXA scan. 291 children (31%) received a cumulated ICS dose equivalent to or above 10 weeks of standard treatment before age 6. We found an inverse association between ICS use and height, −0.26 cm (95% CI: −0.45 to −0.07) per 1 year standard treatment from 0 to 6 years of age, p=0.006. This effect was mainly driven by children with ongoing treatment between age 5 and 6 years (−0.31 cm (95% CI: −0.52 to −0.1), p=0.004), while there was no significant association in children who stopped treatment at least 1 year before age 6 (−0.09 cm (95% CI: −0.46 to 0.28), p=0.64). There was no association between ICS use and BMC at age 6.

Conclusions ICS use in early childhood was associated with reduced height at age 6 years but only in children with continued treatment in the sixth year of life.