C12 Peptide has been promoted for blood pressure control. I could only find one small and brief study regarding the role of C12 peptide in blood pressure control. For suggestions on diet and natural supplements that influence blood pressure, see hypertension. At this point it difficult to say whether C12 peptide will be helpful for blood pressure lowering.

C12 Peptide Research
A randomized, double-blind, placebo-controlled trial of casein protein hydrolysate (C12 peptide) in human essential hypertension.
Am J Hypertension. 2004 Nov;17(11 Pt 1):1056-8. Department of Medicine, Renal Electrolyte and Hypertension Division, University of Pennsylvania, Philadelphia, Pennsylvania
Many patients seek complementary medicine treatments like neutraceuticals for common conditions such as hypertension. We conducted a placebo-controlled prospective randomized crossover study in 10 hypertensive subjects to determine whether a single dose of a hydrolysate of bovine milk protein (designated C12 peptide; low and high dose), either alone or combined with alginic acid (low and high dose), reduced daytime blood pressure (BP), as determined by ambulatory BP monitoring. Within the five treatment regimens a significant reduction of 9 mm Hg in systolic BP at h 6 compared with h 2 occurred on the higher dose of alginic acid (1754 mg) combined with C12. The C12 peptide with the higher dose of alginic acid also showed a significant reduction of 6.0 +/- 2.0 mm Hg in diastolic BP at h 6 compared with h 2. These preliminary data are encouraging and deserve testing in a larger and longer treatment trial.

C12 Peptide Emails
Q. Hi, I came across this advertisement: A group of small peptides (proteins) from the bonito fish, a member of the tuna family are used to create Anti-ACE Peptides. This product lowers blood pressure by inhibiting an enzyme known as ACE (angiotensin converting enzyme). This enzyme causes a reaction that increases both the volume of blood flowing through arteries and the degree of constriction of the blood vessels - like pinching off a garden hose while turning up the flow of water full blast! Anti-ACE Peptides relax arterial walls and reduce fluid volume, inhibiting the enzyme's action. What do you think?
   A. C12 peptide looks interesting, however we can only find one study supporting its use. Long term effectiveness, risks, cautions, etc, are not clear at this time.