A Cup of Blueberries a Day: What It Does for Your Blood Vessels

Key points

One full cup of blueberries a day is a simple habit that helps blood vessels dilate better. In adults with disturbed metabolism this was shown over six months, and the benefit appeared only with a full cup, about 150 g. One measure of artery stiffness also improved. Berries are sold fresh and frozen, and need no preparation.

How to use it

Keep a bag of berries in the freezer and put a cup into a bowl of yoghurt or kefir instead of sweet pastry. A habit tied to breakfast sticks better than "I will eat blueberries when I remember". A cup is about 150 g.

The trials gave powder from dried blueberries equal to a cup of berries. Fresh and frozen berries were not compared directly in these trials, so the main guide is the amount.

What the studies showed

In the longest human trial, 115 adults with a mean age of 63 and metabolic syndrome received for six months a powder from dried blueberries equal to 150 g of berries, or 75 g, or placebo. With the full cup vessel dilation rose by 1.45 percentage points versus 0.39 on placebo (difference 1.06), and the augmentation index fell by 2.24 versus a rise of 0.24 on placebo. Half a cup improved neither vessels nor artery stiffness, and triglycerides rose against placebo (p = 0.01) (Curtis P Am J Clin Nutr 2019. PMID 31136659^[1]).

In 71 participants who were not taking cholesterol-lowering medicine, "good" cholesterol (HDL) was higher on the full cup by 0.08 mmol/L (3 mg/dL) (Curtis P Am J Clin Nutr 2019. PMID 31136659^[1]).

In 48 postmenopausal women with raised blood pressure, 22 g of freeze-dried blueberry powder lowered systolic pressure from 138 to 131 mm Hg and diastolic from 80 to 75 over 8 weeks, while the control group did not change (Johnson S J Acad Nutr Diet 2015. PMID 25578927^[2]).

These are different trials with different people and durations, which is why pressure fell in one and did not change in the six-month trial. The cup of blueberries was most reliable for blood vessels; do not rely on it for blood pressure or insulin resistance.

A real-life example

Picture a person in their sixties with excess weight and disturbed metabolism, like the trial participants. They do not rebuild their life: every morning they eat a cup of berries in yoghurt. That is what was done for six months in the trial, and participants ate 94.1% of the portions they were given (by returned wrappers). So the habit is doable, and people keep it.

What "vessels dilate better" means

A thin layer of cells lines the inside of a vessel. When the body needs more blood, it helps the artery widen. Doctors test this with ultrasound: a cuff squeezes the upper arm, is released, and they see how far the artery opens. The better it opens, the better this layer works. A rise of 1.45 percentage points is a modest but measurable shift in people whose metabolism is already disturbed.

What not to expect

Do not expect quick results: the trial assessed changes after six months. Do not expect half a cup to give "at least something": in the trial half a cup showed no effect. Do not expect lower blood pressure or insulin resistance: in the six-month trial they did not change. And do not expect berries to replace exercise, sleep and work on blood pressure.

Who these data apply to

Participants in the six-month trial were adults aged 63 ± 7, 68% men, body mass index about 31 kg/m², with metabolic syndrome. The blood pressure trial had 48 postmenopausal women. Such studies did not examine these measures in young and healthy people, so the numbers should not be carried over to them.

Who should see a doctor first

Blood pressure, sugar, cholesterol and prescribed treatment stay with your doctor: berries do not replace them, and treatment is not changed on your own. See a doctor if blood pressure stays high on repeat measurements, or with chest pain, shortness of breath or swelling.

Bottom line

A full cup of blueberries a day is a tasty habit with which blood vessels worked better in a six-month trial. Half a cup was not enough, and blood pressure did not change in that trial.