Aspirin AM or PM: Effect on Circadian Rhythm of Platelet Reactivity

Low-dose aspirin is a cornerstone in the secondary prevention of cardiovascular disease (CVD) and is usually taken on awakening, although evidence regarding optimal time of intake is lacking. Platelet reactivity follows a circadian rhythm, with a peak in the morning, contributing to the morning peak of cardiovascular disease. Due to its short half life, aspirin only inhibits platelets which are present at the time of intake. Thus, the timing of aspirin intake may influence its inhibitory effect on platelets and intake of aspirin at bedtime may attenuate the morning peak of platelet reactivity. The time-dependent effect of aspirin on circadian rhythm of platelet function has never been studied before. We hypothesize that aspirin intake at bedtime compared with intake on awakening results in a reduction of the morning peak in platelet reactivity.