Two studies yielded “diametrically opposite results. A paper in the December issue of Hypertension reports that long-term vitamin C supplementation has no effect on blood pressure, while another paper in the same journal reports that vitamin C does lower blood pressure after 1 month in type 2 diabetics.
The two studies yielded "diametrically opposite results," Dr. Laura P. Svetkey, from Duke University in Durham, North Carolina, and Dr. Catherine M. Loria, from the National Institutes of Health in Bethesda, Maryland, note in an accompanying editorial. Therefore, it remains unclear whether vitamin C should be recommended for the prevention or treatment of hypertension.
However, the most important issue, from a public health perspective, may not be whether a particular nutrient, such a vitamin C, influences blood pressure, the editorialists note. Instead, the "key question is how to optimize dietary patterns to prevent and treat high blood pressure," they suggest.
In one study, Dr. Brian A. Mullan, from the Royal Victoria Hospital in Belfast, Northern Ireland, and colleagues assessed the blood pressure-related outcomes of 30 patients with type 2 diabetes who were randomized to receive vitamin C 500 mg or placebo once daily for 4 weeks.
Vitamin C use was associated with significant reductions in brachial systolic and diastolic blood pressures. In addition, vitamin C was linked to improvements in arterial stiffness. In contrast, placebo use was not tied to any hemodynamic effects.
In the other study, Japanese researchers assessed the blood pressure effects of vitamin C use in 378 patients with atrophic gastritis. The group included 244 subjects who received either 50- or 500-mg vitamin C supplementation for 5 years and 134 subjects who did not receive the supplement.
During the study period, all of the groups experienced similar significant increases in systolic blood pressure compared with baseline values. Furthermore, diastolic blood pressure changes were also similar for the three groups. The lack of an association between vitamin C use and blood pressure held true even after accounting for antihypertensive drug use and smoking status.
Because the study populations and treatment durations were different, it is difficult to compare the findings from the two studies, Dr. Svetkey and Dr. Loria note.
Instead of testing the effect of a single nutrient, "perhaps we need to approach dietary research from the opposite direction, first testing which combination of foods…lower blood pressure or prevent the age-related rise in blood pressure," the editorialists state. After this has been done, then "we can begin disentangle the effects of individual nutrients," they add. Hypertension 2002;40:797-803