( and ( it ( ( ( improves ( ( the ability ) ( of ( blood vessels ) ) ) ) ( to ( ( dilate , ) ( which ( reduces ( ( the likelihood ) ( of ( migraine headache ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (CC and) (NP (PRP it)) (VP (VBZ improves) (NP (NP (DT the) (NN ability)) (PP (IN of) (NP (NN blood) (NNS vessels)))) (PP (TO to) (NP (NP (NN dilate)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ reduces) (NP (NP (DT the) (NN likelihood)) (PP (IN of) (NP (JJ migraine) (NN headache)))))))))) (. .)))
and it improves the ability of blood vessels to dilate, which reduces the likelihood of migraine headache.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NN blood) (NNS vessels)) (PP (IN in) (NP (DT the) (NN head)))) (VP (VBP dilate)))) (, ,) (NP (NP (DT a) (NN migraine)) (, ,) (NP (DT a) (JJ severe) (NN headache)) (, ,)) (VP (MD can) (VP (VB occur))) (. .)))