However, higher doses may be even better. In one study, those given 2 grams of vitamin C a day for 30 days had a 10 point drop in systolic blood pressure. This is comparable to the effect you can get with hypertensive drugs such as ACE inhibitors.
Taking high- dose vitamin C makes a lot of sense if you have heart disease, because it does lower LDL cholesterol when given to healthy people, diabetics and people on kidney dialysis, and it has also been shown to reduce arterial thickening. It is also an anti-inflammatory and may help, together with vitamin E, to stop the oxidation, or damage, of cholesterol.
A recent study of almost 60,000 people in Japan reports that vitamin C intake is strongly associated with a reduced risk of heart disease, especially in women, cutting risk by a third. Another reports that vitamin C, with vitamin E, slows down atherosclerosis. Many diet studies also find that the higher your dietary intake of vitamin C the lower your risk. It also lowers risk of diabetes by 62%, if you consume at least 1 gram a day. Diabetics given 1g of vit C have a significant decrease in both their blood sugar levels and glycosylated haemoglobin, as well as triglycerides and cholesterol.
Source - Patrick Holford