Aspirin lowers blood pressure when it is taken at bedtime.

Aspirin lowers blood pressure when it is
taken at bedtime?
Potential health benefits and research finds 2007

Aspirin can reduce blood pressure, most clinical studies find, but the
time for the aspirin administration is critical. Studies have shown that
aspirin produces an administration time-dependent inhibition of
angiotensin II. [6]

Aspirin is a potent antioxidative agent that reduces vascular
production of superoxide, prevents angiotensin II-induced
hypertension, and induces NO release. Low-dose aspirin
administered at bedtime, but not on awakening, has also been
shown to reduce blood pressure, possibly enhancing the nocturnal
trough in NO production. [7]

In 1981, Walter E. reported that long-term aspirin treatment with 1.5
g/day in post-myocardial infarction patients could lead to a
significant increase in systolic and diastolic blood pressure after 6
months. He suggested that nonsteroidal antirheumatic drugs could
produce hypertension in animals, probably due to inhibition of
prostaglandin synthesis. [5]

Similar observation was found in animal studies. Acetylsalicylic acid
(ASA; 0.1-10 mg/kg), indomethacin (IND; 0.1-1.0 mg/kg), and
tartrazine (TZ; 0.1-2.0 mg/kg), given intravenously into guinea pigs
induced dose-dependent increases in mean arterial blood pressure.
[2]

Researchers in Germany treated spontaneously hypertensive rats
of the Okamoto strain with blood pressure above 161 mmHg and
SHR with blood pressure levels of less than 160 mmHg with oral
doses of aspirin (100 mg kg-1) for three days. They found that
aspirin decreased the blood pressure of the rats with blood
pressure above 161 mmHg but increased the blood pressure of the
rats with blood pressure below 160 mm Hg. [3]

Nine men undertook treadmill exercise after pretreatment with
placebo, aspirin and indomethacin. Indomethacin caused a greater
increase in systolic blood pressure during exercise than aspirin and
a smaller fall in diastolic pressure than either placebo or aspirin.
Compared with placebo both aspirin and indomethacin attenuated
to a similar degree the increase in calf blood flow and the changes
in forearm blood flow following exercise. These results suggest that
although aspirin and indomethacin both inhibit prostaglandin
production they have different effects on exercise-induced changes
in blood pressure. [1]

Low-dose aspirin has also been shown to reduce blood pressure
when administered before bedtime, as opposed to upon awakening,
in healthy subjects [8] and subjects with high blood pressure [7] and
pregnant women at high risk for preeclampsia. [6]

In a clinical study of pregnant women at risk of developing
gestational hypertension, Spanish researchers found the
time-dependent effects of aspirin on blood pressure. Aspirin
apparently asserted no effect on blood pressure on awakening,
aspirin apparently reduced blood pressure significantly 8 hours
after awakening and to a greater extent before bedtime. [4]

In a 3 month-study of 328 untreated patients with grade 1
hypertension, 44.0 +/- 12.6 years of age, Spanish researchers
randomly divided the patients into three groups: [a]
non-pharmacological hygienic-dietary recommendations, [b] the
same recommendations and aspirin (100 mg/day) on awakening,
and [c] the same recommendations and aspirin before bedtime.
They found a slightly elevated blood pressure associated with
intake of aspirin on awakening, a significant blood pressure
reduction in the patients who received aspirin before bedtime. [4]

In a 3 month-study of 257 patients with mild hypertension aged at
45+/-13, researchers also found a highly significant blood pressure
reduction in patients who received aspirin at bedtime but not on
awakening. [7]

The ability of angiotensin converting enzyme (ACE) inhibitors to
lower blood pressure may in part be due to the formation of
vasodilatory prostaglandins. Inhibition of prostaglandin synthesis
with aspirin may therefore theoretically attenuate the
antihypertensive effect of ACE inhibitors. However, research studies
have shown that intake of low-dose aspirin does not interfere the
blood pressure-lowering effect of certain angiotensin-converting
enzyme inhibitors (such as enalapril or losartan) [10, 11] and
statins. [9]

ALL RIGHTS RESERVED ZHION 2007. DISCUSS WITH YOUR DOCTOR BEFORE TAKING
ANY SUPPLEMENT OR ASPIRIN. THIS ARTICLE IS FOR YOUR REFERENCE ONLY.

[1] Cowley AJ, et al, Effect of aspirin and indomethacin on exercise-induced changes in
blood pressure and limb blood flow in normal volunteers. Cardiovasc Res. 1985
Mar;19(3):177-80. [2] D'Souza SJ, Biggs DF.Aspirin, indomethacin, and tartrazine increase
carotid-sinus-nerve activity and arterial blood pressure in guinea pigs. Pharmacology.
1987;34(2-3):96-103. [3] Schirner M, Taube C. Different effects of aspirin on blood pressure
of spontaneously hypertensive rats (SHR) with high and spontaneously low levels of blood
pressure. Br J Pharmacol. 1993 Aug;109(4):900-1. [4] Hermida RC, et al, Time-dependent
effects of low-dose aspirin administration on blood pressure in pregnant women.
Hypertension. 1997 Sep;30(3 Pt 2):589-95. [5] Walter E, et al, Does chronic aspirin
treatment increase blood pressure in man? Klin Wochenschr. 1981 Mar 16;59(6):297-9. [6]
Hermida RC, et al, Aspirin administered at bedtime, but not on awakening, has an effect on
ambulatory blood pressure in hypertensive patients. J Am Coll Cardiol. 2005 Sep
20;46(6):975-83. [7] Hermida RC, et al, Differing administration time-dependent effects of
aspirin on blood pressure in dipper and non-dipper hypertensives. Hypertension. 2005
Oct;46(4):1060-8. Epub 2005 Aug 8. [8] Hermida RC, et al, Influence of aspirin usage on
blood pressure: dose and administration-time dependencies. Chronobiol Int. 1997
Nov;14(6):619-37. [9] Magen E, et al, Effects of low-dose aspirin on blood pressure and
endothelial function of treated hypertensive hypercholesterolaemic subjects. J Hum
Hypertens. 2005 Sep;19(9):667-73. [10] Zanchetti A, et al, Low-dose aspirin does not
interfere with the blood pressure-lowering effects of antihypertensive therapy. J Hypertens.
2002 May;20(5):1015-22. [11] Nawarskas JJ, et al, Effect of aspirin on blood pressure in
hypertensive patients taking enalapril or losartan. Am J Hypertens. 1999 Aug;12(8 Pt
1):784-9.