Beet the Cold: The Effect of Inorganic Nitrate Supplementation in Individuals With Raynaud's Phenomenon

Overview

Individuals with Raynaud's phenomenon often experience episodes of reduced blood flow to their fingers and toes during times of stress or cold exposure, causing significant discomfort and pain. Typically, treatment for these individuals involves using drugs like Glyceryl Trinitrate (GTN), which increases blood flow to the fingers and toes by increasing a substance called nitric oxide in the blood. Unfortunately, repeated use of these drugs increases tolerance to them, meaning higher doses are required to produce the same effect. However, increasing the dose can cause more side effects like headaches, and is therefore not considered an ideal long-term therapy. Leafy green vegetables, especially beetroot, contain high amounts of nitrate and are beneficial to blood vessel health, since nitrate from the diet can also be turned into the important blood vessel relaxer, nitric oxide. Unlike GTN, people don't appear to develop a tolerance to dietary nitrate or experience negative side effects. Therefore, this study aims to see if short and longer term beetroot juice supplementation can improve blood flow to the hands and feet in individuals with Raynaud's phenomenon, as well as reduce their pain. This study will tell us how many people are needed for a definitive trial investigating whether beetroot juice can help treat Raynaud's phenomenon. Raynaud's phenomenon can cause significant discomfort and pain to individuals. Dietary nitrate appears to offer a simple, low cost means of improving blood flow to the hands and feet which should reduce both the discomfort and pain experienced characterising this condition. This study will advance our understanding of the causes of Raynaud's phenomenon, specifically the role that the nitrate-nitrite-nitric oxide pathway might play in changing Raynaud's phenomenon symptoms and identifying targets for intervention.

Raynaud's phenomenon (RP) is characterised by a recurrent transient vasospasm of the fingers or toes in response to a cold or stressful stimulus. Nitric oxide (NO•) is a known vasodilator and NO• donors, such as Glyceryl Trinitrate (GTN), improve blood flow in patients with RP and in cold sensitive individuals (Figure 1, see accompanying document). However, individuals develop a tolerance to GTN and show diminishing vasodilatory effects with chronic treatment. In addition, the deleterious side effects such as headaches means that organic nitrates (i.e. GTN and isosorbide mononitrate) are not optimal longterm therapies for RP. Alternative treatments therefore, warrant further investigation. Diets rich in fruit and vegetables has been shown to be effective in reducing blood pressure. In addition, it lowers the risk of morbidity and mortality from cardiovascular disease and are thought to be beneficial to cardiovascular health due to their vasodilatory effects. As diet exhibits such tremendous intra- and inter-individual variation, elucidating which components of such a diet are responsible for this effect is difficult. There is a growing weight of evidence from both human and animal studies that nitrate and nitrite derived from the diet can serve as a source for nitric oxide (NO; please see below), particularly where it is deficient. Indeed, the greatest protective effect on cardiovascular disease is to be found in those diets with the greatest consumption of green leafy and or cruciferous vegetables which typically have high nitrate content. NO is produced in the body in two ways. The first requires the availability the amino acid L-arginine, molecular oxygen, and families of enzymes, the nitric oxide synthases (NOS); that is the NOS pathway. The second pathway is independent of NOS pathway and involves the stepwise enzymatic and chemical reduction of inorganic nitrate to nitrite. A major source of nitrite in humans is the reduction of dietary nitrate by facultative anaerobic bacteria in the mouth. The remaining nitrite is then absorbed into the circulation where it acts as a storage pool for subsequent NO• production, which is expedited in hypoxaemia. Localised hypoxemia such as that observed in the digital vasculature of individuals with RP is a potential therapeutic target for dietary nitrate supplementation. In contrast to organic nitrates (GTN), inorganic nitrate (in the form of beetroot juice) does not cause the same negative side effects or demonstrate tachyphylaxis whilst it does notable improve skin blood flow, microvascular function and lower blood pressure (BP) in healthy individuals and chronic conditions such as hypertension, peripheral arterial disease, heart failure and chronic obstructive pulmonary disease. Thus concentrated beetroot juice (CBJ) may offer an inexpensive, safe and potentially effective intervention to improve the pain and reduced peripheral blood flow characterising individuals with RP. RP can cause significant discomfort and pain to individuals during a vasospasm. Dietary nitrate appears to offer a simple, low cost means of modifying blood flow to the peripheries and, ultimately, reducing both the discomfort and pain experienced by individuals with RP. This study will also advance our understanding of the aetiology and pathophysiology of RP, specifically the role that the nitrate-nitrite-nitric oxide pathway might play in modulating RP symptoms. An understanding of the effects of concentrated beetroot juice on microvascular blood flow and pain may lead to a range of simple, low cost and effective therapeutic interventions to prevent and treat episodes of RP.