A study on the positive effects of vitamin C was performed by Dr Miller at at John Hopkins Univ. The study was reported in sciencedaily and the Maya center [1,2]
Dr Miller found that “…taking an average of 500 milligrams of vitamin C daily reduced blood pressure by 3.84 millimeters of mercury. Among those diagnosed with hypertension, the drop was nearly 5 millimeters of mercury. To see how significant those numbers are let us quote a Table from the National Heart , Lung and Blood Institute 
Systolic (top number) Diastolic (bottom number)
Normal Less than 120 And Less than 80 ( mmHg)
Prehypertension 120–139 Or 80–89
High Blood Pressure > 140 > 90
So 4 to 5 millimeters of mercury is nothing to sneeze at……
But what would make vitamin C decrease your blood pressure?
“…vitamin C may act as a diuretic, causing the kidneys to remove more sodium and water from the body, which helps to relax the blood vessel walls, thereby lowering blood pressure…”
Even though the science daily quotes Dr Miller as being opposed to supplements, it says that 500 mg of vitamin C is contained in 6 glasses of orange juice. That is a lot of juice, and a lot of sugar, so one might be better off with quality supplements…
Another peculiarity of Dr Miller’s study is that the 500mg of vitamin C are quoted as “high dose”. This probably would make enthusiats of the vitamin C megadoses laugh, since they won’t consider anything below several grams, or even twenty, as therapy 
Note that, contrary to popular belief, even though vitamin C is water soluble, there is such a thing as vitamin C overdose, possibly leading to iron poisoning, kidney stones, poor copper absorption, miscarriages 
So more is not necessarily better.
Talk to your Doctor