Data unveiled today at the American Society of Hypertension's Twenty Third Annual Scientific Meeting and Exposition (ASH 2008) revealed for the first time that people with prehypertension who are treated with aspirin may experience significant reductions in blood pressure—but only if they take the pill before bedtime, and not when they wake up in the morning.

People with pre hypertension (a blood pressure reading between normal and high; when systolic blood pressure is between 120 and 139 or diastolic blood pressure is between 80 and 89 on multiple readings) are at significant risk of hypertension, or consistently high blood pressure—the biggest risk factor for heart disease and stroke, the two leading causes of death in the Western world.

“This is the first study to reveal that taking aspirin before bedtime as opposed to upon waking in the morning is an effective strategy to lower blood pressure and cost effective way to individualize treatment regimes in pre-hypertensive patients," said lead investigator Prof. Ramón C. Hermida, Director of Bioengineering and Chronobiology at the University of Vigo in Spain. "These findings therefore have vital treatment implications for these at-risk patients throughout the world.”

The purposeful timing of medications in order to enhance beneficial outcomes or to avert adverse effects is known as ‘chronotherapeutics’. Although factors influencing why aspirin has an impact on prehypertensive patients in the evening and not the morning are somewhat unclear, researchers indicate that it could be because aspirin slows down the production of hormones and other substances in the body that cause clotting. Many of those are produced while the body is at rest.

The study, which ran for three months, involved 244 participants (97 men and 138 women of 43.0±13.0 years of age) all of whom had all received diagnoses for prehypertension. Participants were divided into three groups: non pharmacological hygienic-dietary recommendations (HDR): HDR and a 100mg tablet of aspirin (ASA) on awakening or HDR and ASA at bedtime. Blood pressure levels were monitored at 20 minute intervals from 7:00 a.m. to 11:00 p.m. and at 30-min intervals at night for 48 consecutive hours at baseline and after three months of intervention. Physical activity was simultaneously monitored every minute by wrist (actigraphy) to accurately calculate sleeping and waking blood pressure on an individual basis.

The results showed that those who had taken aspirin before they went to bed (at an average time of 11:00 p.m.), decreased their systolic blood pressure by an average of 5.4 mmHg and their diastolic blood pressure by an average of 3.4 mmHg over the three-month study, without any change in heart rate of physical activity compared to baseline values (p<0.001). This blood pressure reduction was similar during active hours (5.6 and 3.7 mmHg reduction in systolic and diastolic BP, p<0.001) and the nocturnal resting span (5.2 and 3.1 mmHg, respectively). Those who took a morning aspirin, usually at about 8:00 a.m., saw no reduction in ambulatory blood pressure at all, nor did participants in the HDR-only group.