The purpose of this study is to assess the effects of electronic cigarettes-nicotine and electronic cigarette-nicotine free on endothelial function as compared to traditional cigarettes. Due to ethical reasons, we cannot fully randomise all particpants to the three arms.

Participants who wish to quit smoking will be randomized to

1. Switch to electronic cigarettes containing nicotine plus flavor
2. Switch to electronic cigarettes containing flavor alone Those who do not wish to quit smoking will continue on the Tobacco Cigarette arm Treatment period will be 28 days

Electronic cigarettes (EC) are gaining popularity as an alternative to Traditional Cigarettes (TC). Despite not containing all the harmful substances seen in TC, EC are known to contain impurities that may have a detrimental impact on human health. The effects of ECs compared with TC on vascular function, inflammation and oxidative stress are unknown. It is increasingly recognised that nicotine itself has significant atherothrombotic effects. Therefore, clinicians are unable to confidently recommend ECs as a less risky alternative to TC.

Hypothesis: Endothelial function will be improved on EC compared to TC when measured by flow mediated dilatation (FMD).

Potential benefit: This study will provide further information on the potential use these devices and the risks and/or benefits associated with them, specifically in relation to vascular health.

Inclusion Criteria:

• Aged 18 years and over
• Currently smoking ≥15 full strength tobacco cigarettes per day for at least 2 years, or roll-up tobacco equivalent (cigar or pipe smokers not included).
• Willing to stop tobacco cigarettes for period of study if required
• Willing not to use electronic cigarettes if required
• Able to give informed consent

Exclusion Criteria:

• Pregnant or lactating.
• Women of childbearing potential who do not abstain from sex or use effective contraception.
• On current prescribed medication for cardiovascular disease.
• History of cardiovascular disease (excluding hypertension), diabetes, active malignance or chronic renal disease.
• Nut allergy
• Participation in another clinical trial (other than observational trials and registries) with an investigational product and/or intervention within 30 days before visit 1.