The vitamins seem to help because they are antioxidants, the study authors write. The oxygen tanks scuba divers use underwater expose their blood vessels to high levels of oxygen.

When the divers return to the surface, this exposure can leave their blood vessels dilated and can impair the lining of their arteries for days afterward, they write. All it took was a single dose of vitamin C powder (2 grams) and a dose of vitamin E (400 international units) to mitigate the effects.

What the vitamins didn't help, the authors report, was the decrease in lung function and heart output that can be caused by scuba diving.   More detail...