Primary Raynaud's phenomenon (PRP) is characterised by periodic vasospasm of the fingers and toes precipitated by exposure to cold or emotional stimuli and stress. Previous studies have demonstrated that underlying this condition there can be vascular endothelium dysfunction. Pharmacological interventions used to relieve symptoms and complications in PRP include drugs targeted at increasing nitric oxide (NO; transdermal nitrates) levels. Cocoa derived products, rich in the phytonutrients 'flavanols', have been shown to increase the bioavailability of NO at the vascular endothelium and promote vasodilation, which may address an underlying cause of PRP and mitigate symptoms. Previous work carried out in the research group has indicated that the acute consumption of cocoa does not compromise the counter-regulatory responses to localised cold exposure in those with PRP.

30 individuals with PRP will be recruited. Those interested in taking part will attend a medical screening and consent visit. If recruited, a participant number will be assigned to them sequentially and they will be randomised to either experimental or control group, with neither the participants nor the research team knowing which group they have been allocated to. Participants will be asked to complete a diet diary before attending 4 further visits over a period of 3 months.

Visit 1 (pre-intervention) and 4 (end of intervention); immediately on arrival, participants will be asked to lie semi-supine on a hospital bed. Skin temperature (surface thermocouples) and 'core' temperature (infrared tympanic thermometer) will start to be recorded to identify when these parameters have stabilized in room temperature (set at 25oC). Blood pressure will be taken using an arm cuff. Then a Finometer cuff will be attached to the left middle finger to record cardiovascular parameters (Blood pressure /heart rate/ cardiac output) and a laser Doppler probe will be attached to the dorsum of both index fingers to assess skin blood flow. Once the finger skin temperature has remained stable for 6 minutes, baseline Finometer and laser Doppler measurements will be recorded and the skin and 'core' temperature will be noted. Then, the right hand will be placed in a temperature regulated box which is set at an air temperature of 0oC. The hand will be cooled to a finger skin temperature of 15oC, then the box temperature will be modified to maintain the skin temperature at 15oC. The time that it takes for the skin temperature on the fingers to reach 15oC will be recorded. With the finger skin temperature stable at 15oC, Finometer and laser Doppler measurements will be repeated and the 'core' temperature at this point noted. Then, the hand will be removed from the chamber, and allowed to equilibrate in room temperature. The time taken for the skin temperature to reach stability will be recorded, as will the absolute temperature that it stabilises to. Measures above will be repeated once hand temperature is stable. Once these measures have been made, all equipment will be removed and a 15ml blood sample will be taken (for epicatechin, glucose and insulin analysis). The participant will be asked to complete 3 questionnaires (SF-36, Raynaud's symptoms and a food frequency questionnaire). Participants will also return a 4-day diet diary at visits 1 and 4, and their symptom diary at visit 4.

Visits 2 (end of month 1) and 3 (end of month 2); participants will return a 4-day diet diary, symptom diary and any unused capsules. They will also have a resting blood pressure measurement made, weight measured and be asked to complete 3 questionnaires (SF-36, Raynaud's symptoms and a food frequency questionnaire).

At the end of Visits 1, 2 and 3, participants will be given a months' supply of capsules, a symptom diary and a diet diary (to be completed in the week prior to the next visit).