15683
Serum samples were used from a recently performed clinical trial in patients with antibody deficiency or increased susceptibility to respiratory tract infections that were randomized to either placebo or high - dose ( 4000 IU / day ) vitamin D for 12 months .
 vitamin D
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 vitamin D