One of the earliest and most important pathological changes associated with atherosclerosis (hardening of the arteries), heart disease, hypertension, and strokes is endothelial dysfunction.

The endothelium is a layer of cells on the inside of blood vessels and the heart. Because it is adjacent to the bloodstream, the endothelium can signal a blood vessel’s muscle to respond to changes in pressure and inflammation.

Endothelia are considered the “brains” of blood vessels. One human study showed that blueberries improved endothelial function and improved insulin sensitivity, both of which are impaired by metabolic syndrome, a cluster of conditions that increase risk of heart attack, diabetes, and stroke.

Researchers either gave blueberries as a smoothie or a placebo smoothie to 44 adults twice daily for six weeks. They found a significant improvement in endothelial function for blueberry drinkers over the period of the study.

Another study looked at the mechanisms by which blueberries corrected endothelial dysfunction and found that they reduced the inflammatory cytokine TNF-alpha, inhibited the inflammatory cell-signaling component NF-kb, and lowered two factors that caused angiogenesis (ICAM and VCAM).

That is powerful scientific evidence to explain why and how blueberries reduce risk of a heart attack, stroke, and atherosclerosis.

In another interesting animal study, researchers examined the hearts of animals that were made to have a heart attack, and compared the effects of bilberry on the resulting heart damage. Lower doses of bilberry significantly protected the animals’ hearts from damage. On the other hand, using very high doses (way beyond what a person would be exposed to) actually damaged the heart cells.

Human studies have shown that strawberries, blueberries, cranberries, and purified anthocyanins can improve endothelial function, lower blood pressure, reduce arterial stiffness, and correct levels of blood lipids (cholesterol and triglycerides).

Studies have also shown that chokeberries, blueberries, cranberries, blackberries, and strawberries — either fresh, freeze-dried or as purified anthocynanin extracts — could reduce oxidized LDL cholesterol, lipid peroxidation, abnormal lipids, and abnormal glucose metabolism, all of which are associated with heart attacks and strokes.

Importantly, these berries selectively increase the activity of eNOS (endothelial nitric oxide synthase), which increases nitric oxide where it is beneficial — within the blood vessels.

Pomegranate juice has been shown to reduce atherosclerosis, reduce inflammation within blood vessels, lower blood pressure, and remove dangerous free radicals and lipid peroxidation.

Patients with diabetes have high levels of lipid peroxidation, as well as elevated blood pressure and chronic heart damage. Pomegranate juice reduces angiotensin converting enzyme (ACE), which lowers blood pressure, reduces lipid peroxidation, and protects the heart.