To the Editor:

The letter by Zhiqiang Wu, Jiazhang Wu, and Zhibin Lan [1] lists several reasons for how low vitamin D levels may impact respiratory health, including providing additional mechanistic support for our findings, which suggest an association between low vitamin D levels and risk of chest illness in persons with chronic spinal cord injury. However, it should be noted that randomized controlled trials, as referenced in our report, have had mixed results on effects of vitamin D supplementation in preventing chest illnesses.

Guidelines currently exist for supplementing low vitamin D levels primarily to improve bone health [2]. Despite the mixed results of interventional studies, findings from observational studies such as ours suggest that individuals with the lowest vitamin D levels may be at increased risk of respiratory illness and could also benefit from supplementation. Further interventional studies are needed to determine whether vitamin D supplementation is beneficial in preventing respiratory illnesses and, if so, to determine which vitamin D levels should be targeted.