What is Doctor’s Best Sustained Plus Immediate Release Arginine? Doctor’s Best Sustained Plus Immediate Release Arginine promotes a healthy cardiovascular system, enhances healthy circulation and supports heart function. L-arginine has been shown to support the cardiovascular system, through its conversion to nitric oxide. Research suggests L-arginine supplementation may also have positive benefits on athletic performance. Two tablets of Doctor’s Best Sustained Plus Immediate Release Arginine delivers 1000mg L-arginine in a bilayer tablet, with two tablets providing 500 mg of sustained release and 500 mg of immediate release L-arginine. This technology allows for enhanced blood levels of L-Arginine for a continuous period of up to 8 hours. How does it work? Oral L-arginine supplementation has been shown in clinical studies to support various aspects of cardiovascular health. A randomized double-blind placebo-controlled trial found that six weeks of L-arginine supplementation enhanced circulation and supported healthy heart function compared to placebo. The L-arginine effect was due to its role in NO production. Other clinical trials have shown that oral L-arginine supplementation contributes to enhanced exercise tolerance because of its ability to enhance cardiac circulation and vasodilation of blood vessels. L-arginine enrichment of the diet in healthy individuals was shown to support blood pressure already in the normal range. The overall results of these and other clinical trials showed that long-term administration of this amino acid significantly enhanced endothelial function. Why take Sustained and Immediate Release Arginine? The normal aging process in humans has been found to be associated with progressive changes in endothelial function (cells that line the inner surfaces of blood vessels). Research suggests that a major reason for these common changes associated with aging is reduced production or bioavailability of nitric oxide (NO) in vessels and tissues. L-arginine is a substrate for the enzyme nitric oxide synthase, required for the production of nitric oxide in the body. Nitric oxide is a substance critical for the maintenance of normal vascular function. NO mediates a number of physiological effects on the cardiovascular system, including supporting healthy endothelial function, enhancing cardiovascular health and displaying potent antioxidant properties against free radicals.