Hypertension, or high blood pressure, is classified among cardiovascular diseases, which are one of the leading causes of mortality worldwide. Its development is influenced by several factors, among them oxidative stress, which disrupts cellular signalling and causes structural and functional changes in blood vessels, kidneys, and the nervous system. In addition, it promotes systemic inflammation and activation of immune cells, all of which contribute to elevated blood pressure. Due to the increasing number of studies suggesting that oxidative stress may be one of the factors in the development of hypertension, the possibility has emerged that blood pressure regulation could also be influenced by antioxidants, including vitamin C. To determine whether vitamin C affects the reduction of blood pressure, we conducted a systematic literature review that included 435 studies from the PubMed, Google Scholar, and Web of Science databases. Nineteen studies were eligible for systematic review, as they examined the effect of vitamin C on systolic and diastolic blood pressure. All studies were first evaluated for quality, and basic data were extracted and summarized in a table. Of the studies included in the systematic review, 12 provided sufficient data for a meta-analysis. We statistically evaluated the effect of vitamin C on systolic and diastolic blood pressure both in the general population and separately in hypertensive and normotensive individuals. In total, six meta-analyses were performed; however, none demonstrated a statistically significant difference between the experimental and control groups. The most promising results were observed in the meta-analysis assessing the effect of vitamin C on systolic blood pressure in hypertensive individuals, where p-values were very low, suggesting a potential effect, although the number of included studies was very small. For the five studies not included in the meta-analysis, a qualitative comparison was performed. These studies consistently indicated that vitamin C lowers systolic blood pressure — all reported a statistically significant difference between the experimental and control groups — while an effect on diastolic blood pressure was confirmed in only three studies. Although the results of the systematic review and meta-analysis suggest a potential effect of vitamin C on blood pressure, the findings are insufficiently reliable and inconsistent. Therefore, a larger number of studies using standardized methodologies will be required in this field to ensure greater comparability of results.
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