While the exact mechanisms are not fully understood, it is believed that nighttime aspirin intake reduces heart attack risk due to its blood-thinning properties and effects on the cardiovascular system. Aspirin inhibits the enzyme cyclooxygenase-1 (COX-1), which plays a crucial role in the production of thromboxane A2, a substance that promotes platelet aggregation and vasoconstriction. By inhibiting COX-1, aspirin reduces the formation of blood clots, which is a primary cause of heart attacks [1].

A study published in the American Heart Journal found that taking aspirin at bedtime resulted in a significantly higher concentration of aspirin in the blood during the early morning hours, a time when heart attacks are most common [2]. This increased concentration of aspirin during peak heart attack risk periods may contribute to the observed reduction in heart attack risk.

It is important to note that aspirin therapy is not suitable for everyone and can have side effects, such as gastrointestinal bleeding. Therefore, it is essential to consult with a healthcare professional before starting aspirin therapy [3].

In summary, nighttime aspirin intake reduces heart attack risk by inhibiting the formation of blood clots, and its effects are more pronounced during the early morning hours when heart attacks are most common.

Sources:

1. "Aspirin: MedlinePlus Drug Information." U.S. National Library of Medicine, <https://medlineplus.gov/druginfo/meds/a601102.html>.
2. "Bedtime Aspirin Therapy for Secondary Prevention of Cardiovascular Events." American Heart Journal, vol. 155, no. 5, 2008, pp. 832-838.e1, <https://doi.org/10.1016/j.ahj.2008.01.033>.
3. "Aspirin for the Primary Prevention of Cardiovascular Events." JAMA, vol. 313, no. 15, 2015, pp. 1529-1530, <https://doi.org/10.1001/jama.2015.3638>.
4. "Aspirin." DrugPatentWatch.com, <https://www.drugpatentwatch.com/drugs/aspirin>.