Berries are generally considered to be beneficial for a number of human body systems, including the cardiovascular system. Blueberries have been shown to reduce type 2 diabetes and cardiovascular disease risk, both in the short-term and the long-term for normal and at-risk populations.
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The mechanisms by which berries cause these beneficial effects are found to include downregulation of digestive enzymes that act on carbohydrates, upregulation of endothelial nitric oxide synthase, inhibition of foam cell formation and inflammatory gene expression, and decreased oxidative stress.
Composition of blueberries
Fresh blueberries contain 84% water, 9.7% carbohydrates, 0.6% proteins, and 0.4% fat.
Berries are rich sources of polyphenols such as anthocyanins, micronutrients, and fiber. These improve LDL oxidation, lipid peroxidation, total plasma antioxidant capacity, dyslipidemia, and glucose metabolism, thereby resulting in improved cardiovascular risk profiles.
Blueberries, in particular, contain elevated levels of anthocyanidin and flavan-3-ols compared to other berries, while still containing moderate levels of flavonols, fiber, vitamin C, and vitamin E. Of these, anthocyanins are of particular interest for cardiovascular disease, as they have been repeatedly linked to the reduced risk of cardiovascular health complications.
Also, the vitamin C content of blueberries is an average of 10 mg ascorbic acid per 100 g, which equals one-third of our recommended daily intake.
How do blueberries help reduce cardiovascular risk?
One of the major ways through which blueberries reduce the risk of cardiovascular disease is by the inflammation pathway. Cardiovascular disease is often initiated and progresses due to oxidative stress and inflammation.
Anthocyanins, present at high levels in blueberries, have been found to reduce inflammation by reducing the upregulation of inflammatory mediators. When this occurs in vascular endothelial cells, reduced inflammation is beneficial for cardiovascular health.
Cardiovascular disease can also be triggered by metabolic syndrome, which is partly characterized by abnormal lipid contents in the vascular system, known as dyslipidemia. Anthocyanin has been shown to prevent dyslipidemia by manifesting and promoting healthy lipid metabolism. Furthermore, anthocyanins can regulate the distribution of cholesterol, thereby preventing clots and inhibiting pro-inflammatory signaling.
Another pathway through which blueberries help reduce the risk of cardiovascular disease involves anthocyanin mediating an increase in the activity of guanylate cyclase in vascular smooth muscle coupling.
Healthy doses of blueberries
Studies linking the benefits of blueberries for cardiovascular disease typically use moderate volumes and some over extended periods of time. Consuming blueberries once per week has been linked to the reduced relative risk of cardiovascular mortality in shorter-term studies.
Long-term studies, where consumption is monitored over the course of 6 months, showed that daily intake of one cup of blueberries significantly improved cardiovascular function and reduced the risk of associated disease. There was no improvement when half a cup was consumed. However, this study was carried out in patients with metabolic syndrome who are at risk of cardiovascular disease.
The active ingredient of blueberries that is of interest for cardiovascular disease risk management, anthocyanin, has been found to reduce cardiovascular risk at doses of 0.2 mg per day.
Treatment of certain cardiovascular risk groups, such as those afflicted with metabolic syndrome, often involves lifestyle changes, with medications such as statins added as the disease progresses. In order to prevent the need for medication, adding blueberries to the diet is increasingly seen as a key lifestyle modification recommended for those at risk of cardiovascular disease.
Volunteer-led human studies can be quite hard to control because of the lifestyle changes from one individual to another. Therefore, some discrepancies exist between studies.
For example, one long-term study on berry intake surveyed the frequency of consumption and followed up 11 years later with information on cardiovascular disease state. Blueberries were found to not have an association with the risk of cardiovascular disease in this particular study.
The form of berry intervention can also have an effect on the study results. While most studies using whole blueberries have found a reduced risk of cardiovascular disease, some studies using blueberry juice, rather than whole berries, in women found no effect on cardiovascular health.
However, another study using blueberry juice, this time on men, found that there was a significant improvement in cardiovascular health. Therefore, it seems that the benefits of blueberries on cardiovascular health may be gender-dependent, perhaps because of males being more predisposed to poor cardiovascular health compared to women.