Meta-analysis concludes that supplementing with vitamin C is associated with lower blood pressure

On April 4, 2012, the American Journal of Clinical Nutrition published a review by researchers from Johns Hopkins in Baltimore which reports a reduction in systolic and diastolic blood pressure in associated with vitamin C supplementation.

For their analysis, Edgar R. Miller III and colleagues selected 29 randomized clinical trials conducted between 1996 and 2011 that involved the oral administration of vitamin C for at least two weeks. Average pre-treatment systolic blood pressure ranged from 117 to 175 mmHg, and diastolic from 73 to 97 mmHg. The dose of vitamin C used in the studies varied from 60 to 4000 milligrams per day, with a median dose of 500 milligrams daily.

In a pooled analysis of the trials’ participants, vitamin C supplementation was associated with a 3.84 mmHg reduction in systolic blood pressure and a 1.48 mmHg reduction in diastolic pressure. When trials involving patients with hypertension were analyzed, reductions averaged 4.85 mmHg and 1.67 mmHg respectively.

What could explain this? Mechanisms posited for vitamin C in reducing blood pressure include an increase in a cofactor for endothelial nitric oxide synthase (which increases the production of nitric oxide), and improvement of endothelial function of brachial and coronary arteries.

“This meta-analysis is the first quantitative review of randomized trials evaluating the effect of vitamin C supplementation on blood pressure,” the authors announce. “In short-term trials, vitamin C supplementation reduced systolic blood pressure and diastolic blood pressure. Long-term trials on the effects of vitamin C supplementation on blood pressure and clinical events are needed.”