Diastolic blood pressure, the bottom number in a blood pressure reading, is primarily determined by how much resistance your smaller blood vessels create while your heart rests between beats. A normal diastolic reading is below 80 mm Hg, stage 1 hypertension starts at 80 to 89 mm Hg, and stage 2 hypertension is 90 mm Hg or above. Unlike systolic pressure, which depends heavily on the flexibility of your large arteries, diastolic pressure reflects what’s happening in your smaller arterioles and how elastic your arterial walls remain over time.
Peripheral Vascular Resistance
The single biggest driver of diastolic pressure is how tightly your small blood vessels constrict or relax. When these arterioles narrow, blood meets more resistance as it flows through, and pressure stays elevated even during the pause between heartbeats. Anything that increases this resistance, whether it’s chronic inflammation, hormonal signals, or structural changes in the vessel walls, pushes diastolic readings higher.
In adults under 50, rising diastolic pressure almost always points to increased vascular resistance. The vessel walls are still relatively flexible at that age, so the reading is a fairly clean signal of how constricted the arterioles have become. In younger adults (ages 20 to 39), even modestly elevated diastolic pressure carries real cardiovascular risk: one large study found that stage 1 isolated diastolic hypertension raised the risk of cardiovascular events by 32%, and stage 2 raised it by 82%, compared to people with normal blood pressure.
How Aging Changes the Pattern
Diastolic pressure doesn’t climb indefinitely. It typically rises through early and middle adulthood, peaks around age 55 in men and 58 in women, and then gradually falls. The reason is arterial stiffness. As the large arteries lose elasticity with age, they absorb less of the pulse wave from each heartbeat. That pushes systolic pressure up but actually allows diastolic pressure to drop because the stiffened arteries recoil less effectively during the resting phase.
People whose arteries stiffen faster hit this turning point earlier. Research from the American Heart Association found that individuals in the top quarter of arterial stiffness saw their diastolic pressure peak and start declining around age 51, nearly a decade earlier than those with the most flexible arteries, who didn’t reach the turning point until about age 60. This is why older adults often have a wide gap between systolic and diastolic numbers: their systolic keeps climbing while their diastolic drifts downward.
Hormones That Raise Vascular Tone
Several hormones directly influence how tightly your blood vessels constrict, which makes them powerful regulators of diastolic pressure.
Aldosterone, a hormone produced by your adrenal glands, causes your kidneys to retain sodium and water. That expands blood volume, which initially raises pressure by increasing the amount of blood your heart pumps. Over days to weeks, though, aldosterone also directly constricts blood vessels in the gut and elsewhere, sustaining higher pressure even after the heart’s output normalizes. Conditions like adrenal tumors or chronic kidney disease can cause excess aldosterone production, and the resulting blood pressure increase develops slowly, often over weeks.
Cortisol, your body’s main stress hormone, works differently. It raises blood pressure quickly, within hours, by shifting fluid into the bloodstream and increasing cardiac output. Chronic stress, sleep deprivation, and conditions like Cushing’s syndrome all elevate cortisol levels, which can keep diastolic pressure persistently higher than it should be.
Insulin Resistance and Body Weight
Carrying excess weight raises diastolic blood pressure through several overlapping mechanisms. Fat tissue is metabolically active and promotes low-grade inflammation, which stiffens blood vessel walls. But the link between weight and diastolic pressure goes deeper than that.
Insulin resistance, a condition where your cells respond poorly to insulin and your body compensates by producing more of it, reduces blood flow to skeletal muscles and promotes structural changes in the heart. High circulating insulin levels stimulate growth of heart muscle tissue and encourage the buildup of fibrous tissue between heart cells, making the heart stiffer and less efficient at filling during its resting phase. Research has confirmed that higher insulin levels correlate directly with worse diastolic heart function in people with hypertension. Because insulin resistance is closely tied to abdominal obesity, losing weight often improves both insulin sensitivity and diastolic pressure simultaneously.
Sodium Intake
Sodium raises blood pressure by pulling water into the bloodstream, increasing the volume of fluid your heart has to pump and the pressure against vessel walls. A crossover trial published in JAMA found that switching from a high-sodium diet to a low-sodium diet reduced diastolic blood pressure by about 3 mm Hg within just one week. That may sound modest, but population-wide, even small reductions translate into meaningful drops in heart attack and stroke risk. The effect tends to be larger in people who are already salt-sensitive, a trait that becomes more common with age and is more prevalent in Black adults.
Exercise and Physical Activity
Regular aerobic exercise, things like brisk walking, cycling, or swimming, is one of the most consistent ways to lower diastolic pressure without medication. Studies show drops of 5 to 8 mm Hg in diastolic readings with regular aerobic activity. The effect comes from improved blood vessel flexibility, reduced resting heart rate, and better regulation of the hormones that control vascular tone.
You don’t need marathon training to see results. Most of the benefit comes from 150 minutes per week of moderate-intensity activity. Resistance training also helps, though its effects on diastolic pressure specifically are smaller than those of cardio. The combination of both types tends to produce the best overall cardiovascular benefit.
Alcohol Consumption
Alcohol has a complicated relationship with diastolic pressure. In the hours immediately after drinking, blood pressure actually drops, with one analysis finding an average diastolic decrease of about 8 mm Hg roughly five hours after consumption. This short-term dip is caused by alcohol’s vasodilating effect: it relaxes blood vessel walls temporarily.
The rebound, however, pushes pressure in the other direction. Across studies, regular daily alcohol intake raised diastolic pressure by an average of 1.4 mm Hg. Heavier drinking magnifies the effect substantially. The pattern matters more than the total amount: binge drinking creates sharp swings in vascular tone that appear to be harder on blood vessels than the same weekly volume spread across smaller daily amounts.
Other Contributing Factors
Several additional factors influence diastolic pressure in ways worth knowing about. Chronic kidney disease impairs your body’s ability to regulate fluid balance and sodium excretion, often raising diastolic pressure as an early sign. Obstructive sleep apnea causes repeated surges of stress hormones overnight, which can keep diastolic readings elevated even during the day. Caffeine produces a temporary spike in both systolic and diastolic pressure, typically lasting a few hours, though regular coffee drinkers develop some tolerance to this effect.
Certain medications can also shift diastolic readings. Nonsteroidal anti-inflammatory drugs (like ibuprofen), decongestants, and some antidepressants promote fluid retention or vasoconstriction that raises diastolic pressure. If your diastolic readings have crept up without an obvious explanation, a medication review with your pharmacist or doctor can sometimes identify the cause.