High Blood Pressure: Nightly Aspirin May Help

Sept. 15, 2005 -- Taking aspirin at night may help lower blood pressure more than taking aspirin in the morning, new research shows.

It's the first finding of its kind. More studies are needed to check the results before recommendations can be made.

The study was done in Spain. The researchers included Ramón Hermida, PhD, of the University of Vigo. Their report appears in the Journal of the American College of Cardiology.

Aspirin Schedule

Hermida's study included 328 people with mild, untreated stage 1 high blood pressure. Stage 1 high blood pressure is defined as a systolic reading (top number) of 140-159 and a diastolic reading (bottom number) of 90-99.

The patients were about 44 years old, on average.

All of the patients got advice on lowering their blood pressure without medicine (including dietary recommendations for high blood pressure). They were split into three groups.

One group wasn't given any aspirin (169 people). A second group took 100 milligrams of aspirin every morning (77 people). A third group took the same dose of aspirin at night (82 people).

All patients wore devices that monitored their blood pressure around the clock. Blood pressure readings were automatically recorded every 20 minutes during the day and every half hour at night.

Study's Results

After three months, these were the results:

• Aspirin at night: Significant drop in blood pressure
• Aspirin in the morning: Slightly higher blood pressure
• No aspirin: Slightly lower blood pressure

The biggest blood pressure change was in the patients who took aspirin at night, the study shows.

How much did their blood pressure drop?

• Systolic blood pressure (the top number): down 6.8
• Diastolic blood pressure (the bottom number): down 1.6

In people older than 50 a systolic blood pressure greater than 140 is a much more important risk factor for heart disease than the diastolic blood pressure reading.

Nearly nine out of 10 who took aspirin at night had a drop in blood pressure, the study shows.

The reasons for the time trends aren't clear, according to the researchers. The topic deserves further study, they write.

Second Opinion

The results are "surprising and thought provoking" and the potential implications for blood pressure treatment are "most important," writes Franz Messerli, MD, FACC, in a journal editorial.

Messerli, who works at St. Luke's Roosevelt Hospital Center in New York, writes that he "wholeheartedly agrees" that more studies are needed.

But he's not totally sold on the idea that taking aspirin at night eases high blood pressure.

Many questions need to be answered before low-dose bedtime aspirin can be routinely recommended for high blood pressure, notes Messerli.

"As provocative as these findings are, they originate from a single source only," he writes, calling for "extreme caution" in interpreting the results.