Harvard Heart Letter

Heart Beat: Blood pressure reading affected by eating

Heart Beat

Blood pressure reading affected by eating

When you check your blood pressure, or have it measured by a nurse or doctor, it's important to sit quietly for a few minutes beforehand. Not eating for two to three hours is another way to help you get the most accurate reading possible, according to a comprehensive study by Australian researchers.

They asked 38 volunteers to fast overnight, then come to a clinic for a series of blood pressure measurements. Once the "baseline" pressure had been measured, the volunteers ate a breakfast consisting of toast, margarine, jam, and water. As soon as they were finished eating, the researchers checked their blood pressure again, and then every 15 minutes for two hours. Blood pressure went up immediately after the meal, but then it began to fall, reaching a low point about 45 minutes after the meal and gradually climbing back to the pre-meal level over the next 90 minutes or so. For systolic pressure (the top number of a blood pressure reading), the low point was an average of 3 points below the baseline pressure, while diastolic pressure (the bottom number) fell an average of 4 points (American Journal of Clinical Nutrition, August 2009).

Although these meal-induced changes are seemingly small, they could make a difference. In the study, four of the volunteers had systolic blood pressures above 130 (the cutoff for high blood pressure) before eating. But only one had high blood pressure when it was measured 30 to 50 minutes after eating.

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