What Time of Day Is Your Blood Pressure Highest?

Blood pressure typically rises around 6:00 a.m. as you start to awaken from sleep and peaks around 10:00 a.m., commonly known as the “morning surge.” However, not everyone follows this pattern, and some will experience “reverse dipping,” in which the nighttime blood pressure is higher than the daytime blood pressure.

What Causes Blood Pressure to Fluctuate?

Numerous physiological and biochemical events contribute to morning blood pressure surges. These are primarily directed by the body’s internal clock, known as the circadian rhythm, which regulates the sleep-wake cycle.

Circadian rhythms are mainly influenced by changes in light from night to day. Decreased light after sunset triggers the release of hormones like melatonin (which promotes sleep), while increased light at sunrise signals the release of cortisol (which promotes wakefulness).

During the cycle, the brain shifts dominance between the two branches of the autonomic nervous system (ANS), which regulates involuntary functions like blood pressure.

These two branches are known as:

• Parasympathetic nervous system: This part of the ANS manages the “rest-and-digest” function at night. In addition to promoting sleep, the release of melatonin triggers vasodilation (widening of blood vessels), resulting in a 10% to 20% drop in blood pressure.
• Sympathetic nervous system: This part of the ANS prepares the body for action, including the body’s “fight-or-flight” response. In addition to promoting wakefulness, cortisol triggers vasoconstriction (narrowing of blood vessels), contributing to morning surges.

What Influences Fluctuations?

Other factors can contribute to cyclic blood pressure changes, including the extent to which blood pressure increases during the morning surge.

These include:

• Older age: Arterial stiffness and changes in the ANS with age can make the morning surge more pronounced in older adults.
• Hypertension: Pre-existing high blood pressure overactivates the sympathetic nervous system, leading to an exaggerated spike in blood pressure.
• Diabetes: Poorly controlled blood sugar also overstimulates sympathetic nerves, leading to higher blood pressure in the morning.
• Chronic kidney disease (CKD): Decreased kidney function causes fluid retention, which independently increases blood pressure.
• Alcohol: The effect of alcohol on the morning surge is dose-dependent, with evening binges causing more pronounced increases in blood pressure.
• Stress: Anxiety, depression, and general psychological stress trigger the release of cortisol as part of the body’s stress response.
• Sleep problems: Insomnia, sleep apnea, and shift work disorder (SWD) interrupt circadian rhythms and can also increase arterial stiffness over time.
• Ambient temperature: Morning surges tend to increase in winter as cold temperatures cause vasoconstriction, and decrease in summer as warm temperatures cause vasodilation.

When Are Morning Surges a Medical Concern?

In healthy people, a transient increase in the morning blood pressure is normal and generally of no concern. However, abnormal, persistent increases may be an indication of a major cardiovascular concern, even in people with normal blood pressure.

Masked hypertension occurs when blood pressure readings in a healthcare provider’s office are normal (less than 120/80 mmHg) but high at home. This is especially true when morning readings are consistently 130/80 mmHg or higher (the clinical definition of hypertension).

Studies suggest that one in eight adults in the United States—or roughly 17 million people—have masked hypertension.

This is of major concern given that the risk of death from a heart attack or stroke is nearly the same with masked hypertension as it is with “regular” sustained hypertension.

Among people with hypertension, the effects may be far worse. According to a 2023 study, adults with hypertension who experience a 10 mmHg surge in their systolic (upper) blood pressure in the morning are at:

• 177% greater risk of hospitalization for heart failure
• 192% greater risk of a heart attack
• 194% greater risk of atrial fibrillation
• 232% greater risk of stroke
• 270% greater risk of cardiovascular death

Does Everyone Experience Morning Surges?

Not everyone experiences morning surges in blood pressure. Some people, known as “reverse dippers,” have the opposite reaction, experiencing drops in blood pressure in the morning and sustained or higher blood pressure readings while asleep.

Reverse dipping affects around 13% of adults and is of concern whether or not a person has hypertension.

By exposing the body to sustained high blood pressure at night, multiple organs can sustain significant damage over time, increasing the risk of:

• Cardiovascular disease: Reverse dippers have a two-fold increased risk of heart disease compared to those with normal morning surges.
• Diabetic heart disease: Reverse dipping with diabetes is linked to a three-fold increased risk of cardiac autonomic neuropathy (CAN) and a two-fold increased risk of death from all causes.
• Dementia: Reverse dipping in older males increases the risk of dementia by any cause by 1.64-fold and the risk of Alzheimer’s disease by 1.67-fold.
• Kidney damage: Reverse dipping in people with CKD increases the risk of a major kidney event by threefold and the risk of death from all causes by fivefold.

What Can You Do?

If you have excessive morning blood pressure surge, certain lifestyle changes may help, including:

You can also meet with your healthcare provider to explore medication adjustments or rule out underlying causes.

If you have hypertension, be sure to take blood pressure readings several times a day rather than just in the morning, as reverse dipping can create the false impression that your blood pressure is under control.

If needed, your healthcare provider can also organize a 24-hour blood-pressure monitor.