VITAMIN C AND BLOOD PRESSURE

The past few years have not been very kind to antioxidant vitamins like Vitamin C, Vitamin E, and Vitamin A and its derivatives. Large-scale, high-powered prospective clinical trials have recently dashed prior hopes that these vitamins can significantly reduce the risk of cancer or cardiovascular disease. Despite intriguing results from earlier and much lower powered research studies, we simply have not been able to show that any of these potential health benefits are associated with antioxidant vitamin supplements in humans. However, a new clinical research study in the Nutrition Journal suggests that there may still be some potential long-term cardiovascular health benefit from high Vitamin C levels in the blood.

High blood pressure is generally defined as a systolic blood pressure (the “top number”) greater than or equal to 140 mm Hg, or/and a diastolic blood pressure (the “bottom number”) greater than or equal to 90 mm Hg. As we age, our blood pressure tends to gradually rise, and by the time we reach our 60s, the majority of us will have elevated blood pressure. Hypertension is known as “the silent killer” for good reason, as it can cause gradual, asymptomatic, and irreversible damage to the body’s vital organs, including the heart, brain, and kidneys, if left untreated.

More than 240 African-American and Caucasian women participating in a large prospective study (the National Heart, Lung and Blood Institute Growth and Health Study) were evaluated in this smaller study. All of these women were between 18 and 21 years of age when they enrolled in this large public health study. During their 10th year of participation in this ongoing clinical study, blood levels of Vitamin C were measured in all of these women. Blood pressure readings during the 9th and 10th years of participation were then analyzed as a function of Vitamin C levels in the blood of these 242 patient volunteers. These patient volunteers were then divided into 4 groups, based upon the level of Vitamin C in their blood.

The women in the group with the highest blood levels of Vitamin C had, on average, significantly lower systolic and diastolic blood pressure readings when compared to the women in the group with the lowest Vitamin C levels, even after adjusting for differences between the two groups of women in terms of other hypertension risk factors like race, obesity, dietary intake of fat and salt, and education levels. The average systolic blood pressure among the women with the highest levels of Vitamin C in their blood was almost 5 mm Hg lower than the systolic blood pressure among the women with low Vitamin C levels. Likewise, the average diastolic blood pressure reading among the women with highest Vitamin C levels was 6 mm Hg lower than what was observed among the women with very low Vitamin C levels in their blood.

When blood pressure readings in the 10th year of this study were compared with the blood pressure results from the previous year, higher Vitamin C levels also appeared to be associated with a smaller annual increase in blood pressure when compared with very low Vitamin C levels.

Thus, in this prospective clinical research study, high levels of Vitamin C in the blood appeared to be linked with, on average, lower blood pressure readings and with significantly less increase in blood pressure readings over a period of one year.

While the results of this cohort study are very intriguing there are, as always, a few caveats that must be mentioned. First of all, this study did not link dietary Vitamin C intake with Vitamin C levels in the blood, so it is not possible to know, from this study, if a diet rich in vitamin C (which is rapidly excreted from the body following ingestion) resulted in the higher blood levels of this vitamin that were observed, or if there are other factors, including genetic factors, that determine a person’s average Vitamin C levels in the blood. Similarly, if genetic factors are primarily responsible for the level of Vitamin C in the blood, these same genetic factors could also be affecting blood pressure independent of any direct action by Vitamin C. Also, while this study of young women strongly suggests that high levels of Vitamin C in the blood may decrease the natural rise in blood pressure that occurs with aging, it cannot yet tell us if these favorable changes in blood pressure, presumably due to Vitamin C, will be sustained as these women grow older. This study also cannot tell us whether or not, in the long run, the apparently favorable effects of Vitamin C on blood pressure will actually lead to any clinically significant improvements in health, either.

Given the recent drumbeat of dismal news regarding the antioxidant vitamins and other related dietary supplements, this small study does offer some hope that Vitamin C might still be associated with potential health benefits beyond its primary role in the synthesis of collagen (a critical structural protein found throughout the body). However, it will take many more years before we know whether or not Vitamin C supplementation can truly reduce the inexorable rise in blood pressure that occurs with aging, and if so, whether or not this effect has any clinically meaningful impact on health.