Recent research has demonstrated that insertion and rotation of acupuncture needles stimulates the body to produce adenosines. These naturally occuring chemicals have a wide range of potential functions. They help to regulate sleep, can increase energy, help certain heart and lung conditions, encourage vasodilation, assist wound healing, have anti-inflammatory properties, inhibit local nerve signals to ease pain, and create nerve signals that lead the brain to stimulate the release of natural painkilling endorphins.
The research also indicated that the effects of adenosine may be negated by individuals consuming large quantities of methylxanthines, which is the caffeine found in coffee. Theophylline (the caffeine in tea) and theobramine (chocolate) can also have this effect but are generally present in lower quantities.
This helps to provide a western bio-medical context to why many acupuncturists discourage coffee consumption by their patients.