Short-term units of vitamin C supplementation can reduce systolic and diastolic BP, indicated a systematic review and meta-analysis of clinical trials. 

Increased vitamin C intake, vitamin C supplementation, and higher blood concentrations of vitamin C have been associated with lower BP. Despite this, evidence from clinical trials regarding the BP-lowering effects of vitamin C is inconsistent. Now, an analysis of 29 clinical trials examining the effects of short-term vitamin C supplementation on BP has demonstrated some benefit.

The median dose of vitamin C supplementation was 500 mg per day over a median duration of eight weeks. The trials included 10 to 120 participants. The pooled changes in systolic BP (SBP) and diastolic BP (DBP) were -3.84 mm Hg and -1.48 mm Hg, respectively. In trials involving persons with hypertension, SBP fell by 4.85 and DBP decreased by 1.67. 

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Long-term trials on the effects of vitamin C supplementation are needed, contend the investigators (Am J Clin Nutr. 2012;95:1079-1088). According to a different study, neither short-term nor long-term use of another substance related to BP will protect people from colorectal cancer (CRC).

Beta blockers might reduce the risk of CRC due to the weakening of norepinephrine signaling. After studying 1,762 persons with CRC and 1,708 control individuals in Germany, Lina Jansen, MSc, and colleagues reported in the journal Cancer that they found no association between beta blocker use and CRC risk reduction. In fact, the team noted a connection between long-term use of the drug (six years or longer) and risk of stage IV CRC.