Whether or not vitamin C (ascorbic acid) lowers blood pressure has been somewhat controversial, with some studies suggesting that it does, while others found no effect. It has also been suggested that one of the reasons why the DASH (Dietary Approaches to Stop Hypertension) diet lowers blood pressure is because the fruits and vegetables which it contains are rich in vitamin C.

A new study in which 68 men with mostly normal blood pressures were fed diets which had varying amounts of vitamin C has now looked at this question again. The participants were provided with different foods to eat over a 17-week period. During the later part of the study they had their blood pressure measured while they were fed a diet that was high in vitamin C (117 milligrams a day) for one month, then a diet that had very little (9 milligrams) for a second month, followed by the high C diet for a third month. The high C diet was associated with a reduction of about 1 mmHg of systolic pressure, and 2 mmHg of diastolic. There was also a correlation between the blood levels of vitamin C and blood pressure.

Doctor's Comments

The way this study was conducted enabled the detection of quite modest changes of pressure in response to the dietary changes. The changes are consistent with the findings of the DASH study, in which it was found that a diet rich in fruits and vegetables resulted in a modest reduction of blood pressure (in DASH, the biggest changes were seen when low-fat dairy products were added). The amount of vitamin C used in this study was not large, and the low and high intakes in the study were equivalent to a little less and a little more than what the average American consumes. The study did not investigate the effects of mega-doses of vitamin C -- some studies have used up to 2 or 3 grams (2000 to 3000 milligrams). An interesting aspect of the study is that African-Americans, who tend to have higher blood pressure than whites, also have somewhat lower blood levels of vitamin C (presumably because they eat less of it), so this may be one reason for the higher blood pressure in African-Americans than in whites. Of all the supplements that people commonly take, vitamin C is the only one for which there is consistent evidence that it lowers the blood pressure.