Aspirin (acetylsalicylic acid, ASA) has a protective effect against second (and subsequent) cardiac events which has been well-documented for decades. Its effect is mediated via its inhibition of platelet stickiness clumping of platelets is a key factor in clotting, an important cause of heart attacks and strokes.
About 30 years ago, it was discovered that cardiovascular events, especially heart attacks, are more common in the morning and, perhaps not coincidentally, platelets are stickier in the morning as well. These findings inspired Dutch researchers to determine if there was indeed a differential effect of ASA upon platelets, depending on the timing. The researchers wanted to see if taking aspirin at night could better thin a person's blood and potentially lower their heart attack risk, said study author Dr. Tobias Bonten to WebMD. Bonten serves in the department of clinical epidemiology at Leiden University Medical Center in the Netherlands.
Presented at the American Heart Association meetings earlier this week, the Aspirin in Reduction of Tension II trial is the first study to explore the timing of aspirin intake among cardiovascular disease patients. In the randomized, open-label study, 290 patients with a history of prior heart attack took either 100 mg of aspirin upon waking or at bedtime during two 3-month periods. At the end of each period, blood pressure and platelet activity was measured.
The researchers found that taking aspirin at bedtime reduced platelet activity more than taking it in the morning, apparently because it prevented the body's normal morning surge in platelet activity. Blood pressure was not reduced; however, bedtime platelet activity was reduced by 22 units (aspirin reaction units).
ACSH s Dr. Gilbert Ross had these comments: First of all, this is a small and preliminary study, and neither double-blinded nor journal-published. More importantly, no actual outcomes relevant to heart disease were found (nor was it sought). In fact, I am surprised that they found such an effect at all, given that aspirin inhibits platelet aggregation for about 2 months, or more. This was just a hypothesis-generating study; the next step would be a randomized controlled prospective study comparing a large group of heart patients divided into three parts: aspirin at night, or in the morning, or no aspirin at all (placebo-control group), then followed for a year or two, perhaps, to see the comparative incidence of vascular events.