Many factors can cause blood pressure fluctuations

My blood pressure readings vary throughout the day. Sometimes they’re high and sometimes they’re low. So I’m not sure if I have high blood pressure or not.


Santa Monica

Blood pressure varies throughout the day and is influenced by a number of factors, says Dr. Joshua Penn, a cardiologist with Cedars-Sinai Medical Group and in private practice in Beverly Hills.

For starters, all humans have a natural daily rise and fall in blood pressure that corresponds with their circadian rhythm.

For most people, blood pressure will be at its lowest in the early morning hours and then rise through the late morning and peak in midafternoon.

Typically, this range will be about 10 to 15 millimeters of mercury on the upper, or systolic, value, which represents the peak pressure in the arteries; and five to 10 millimeters of mercury on the lower, or diastolic, value, which represents the lowest pressure at the resting phase of the cardiac cycle.

Thus, a person with a resting blood pressure of 125/70 at 3 a.m., might have a reading of 140/80 by late afternoon.

Other factors contribute to fluctuations in blood pressure, but the most common one is hypertension, a condition characterized by chronic high blood pressure.

“When a person has a history of hypertension, or if the blood pressure has not been well-controlled over a period of years, then the vessels themselves become more reactive, meaning they tighten up with less provocation than they would in an average person,” Penn says.

One of the manifestations of poorly controlled blood pressure is a high degree of variability, he says. A person with a lot of variation could easily have a blood pressure of 140/90 in the morning and a reading of 200/100 later in the day.

Other factors, such as stress, emotional upsets and food sensitivities can cause an increase in blood pressure. Someone who is salt sensitive, for example, could get a double-digit boost from a big dose of salt. Certain street drugs, such as cocaine and methamphetamine, can cause a spike.

Finally, there’s a phenomenon known as “white coat hypertension,” in which the stress of a visit to the doctor’s office causes an elevation in blood pressure.

On the other side of the coin, alcohol, cessation of exercise and a warm environment can lower blood pressure.

Penn has found home blood pressure devices (particularly the ones that measure blood pressure at the biceps, rather than the wrist or finger) to be reasonably accurate — “usually within 10 points on the upper and five on the lower. They can actually be quite helpful,” he says.

Many physicians think that optimal blood pressure is below 120/80 and that blood pressure from 120/80 to 139/89 signifies that the patient may be at risk for hypertension. Blood pressure above 139/89 in several readings would be considered mild hypertension.

“We know from data that lower natural blood pressure is associated with longevity,” Penn says.

Hypertension, which is partly genetic and tends to increase with age, can usually be controlled with proper medical attention, diet and exercise.

— Janet Cromley