In one lung rehabilitation study, 50 people, average age 67, with a history of COPD flare-ups took 100,000 IU of vitamin D per month (equal to 3,333 IU per day) or a placebo.
After three months, while the placebo group did not change, the vitamin D group saw levels of vitamin D increase from 22 to 53 ng/mL.
The vitamin D group utilized more oxygen while the placebo group utilized less, and walking distance increased 118 feet in six minutes for vitamin D compared to increasing 36 feet for placebo.