Are Blueberries Good for Your Heart and Brain?
By Chloe Arzy
Does an apple a day keep the doctor away? Based on what we know about the health benefits of eating apples, in particular when they become a regular component of our diet, the answer is a definite yes. Fruits and vegetables are one of the pillars of a healthy diet. In addition to this general recommendation, studies have shown that there are different benefits from each subgroup of fruits. Berries, in particular, have attracted a lot of attention as they contain high amounts of flavonoid polyphenols. Blueberries and lingonberries were found to contain 1100 mg/100 g dwt of flavonoids, which is almost twice the content of raspberries and strawberries. Anthocyanins are the dominant flavonoids in all berries. Berries also contain significant amounts of dietary fiber, which amongst berries’ many health benefits help to regulate blood sugar and reduce the risk for dyslipidemia. In particular, blueberries have attracted much attention as epidemiological studies suggest they can reduce the risk of cardiovascular disease (CVD).
CVD is commonly associated with co-morbidities such as high blood pressure, type 2 diabetes, obesity, and dyslipidemia all of which increase the risk for CVD. In a systematic review and meta-analysis of randomized controlled trials, the supplementation of blueberry powder was found to have a favorable impact on reducing body weight, and “significant weight loss was indicated from studies longer with a follow-up of more than 6 weeks or with blueberry powder or freeze-dried blueberry”. When viewed together, these results demonstrate that the supplementation of blueberries in one’s diet in combination with other lifestyle modifications can help reduce the risk for obesity and for low grade systemic immune activation, thus reducing the risk for CVD. In regards to dyslipidemia, a meta-analysis of clinical studies analyzed the effects of Vaccinium berries (a genome of plants consisting of blueberries, cranberries, lingonberries, and bilberries) intake on serum lipids when consumed as whole fruits, juices, purified extracts, and capsules. Among these studies, the average consumption of anthocyanins ranged from 2.1 mg/d – 742 mg/d and the duration of intervention ranged from 2-24 weeks. These studies showed that in patients with elevated blood lipids, regular berry intake could lower “bad” cholesterol (LDL cholesterol) while increasing the “good” cholesterol (HDL cholesterol).
“Based on the emerging evidence, dietary berries and berry products hold promise as a natural and alternative means to lower blood lipids in adults with CVD risks.”
In addition to their high concentration of the polyphenol anthocyanin, blueberries also contain significant amounts of dietary fiber. Amongst their many health benefits, dietary fiber has also been shown to decrease “bad” cholesterol blood levels, while a deficiency of fiber intake is associated with an increased risk for CVD. The complex carbohydrates making up dietary fiber are metabolized by the gut microbiota into different types of short chain fatty acids, including butyrate. Amongst its many beneficial functions, butyrate reduces the intestinal absorption of cholesterol, and leads to a reduction in cholesterol blood levels. In one experiment, investigators evaluated the effects of dietary fiber on cholesterol concentrations, and based on their results concluded that dietary fiber intervention decreased plasma concentrations of “bad” cholesterol (LDL cholesterol). The mechanism of the cholesterol lowering effect of fiber was demonstrated by showing a reduction in cholesteryl ester transfer protein activity leading ultimately to a reduced formation of “bad” cholesterol. At the same time, an increase in the turnover of LDL-Apolipoprotein B-100 (LDL-ApoB), the dominant protein found on the surface of “bad” cholesterol (LDL cholesterol) was found. This higher turnover lead to a faster clearance of LDL-ApoB. LDL-ApoB concentrations can be measured to determine one’s risk of CVD, the higher levels of these proteins corresponding to an increased risk for CVD.
“Increasing dietary fiber intake with natural foods is associated with reductions in classical and novel cardiovascular risk factors”
The intake of wild blueberries has shown to improve cognitive performance and vascular function in healthy individuals. In a double-blind randomized trial, 61 healthy older individuals aged 65-80 years old were either given 26 g of freeze-dried wild blueberry powder which is equivalent to 3/4 cups of fresh wild blueberries, or a matched placebo for 12 weeks. Results showed that there was a significant increase in flow-mediated dilation, meaning more efficient blood circulation. Additionally, the study showed a reduction in 24 hour ambulatory systolic blood pressure in the group that consumed wild blueberry powder compared with the placebo group. The wild blueberry group also performed with better accuracy on immediate recall on the auditory verbal learning task, which measures an individual’s ability to recall and recognize items that they have previously heard. They also showed improved responses in the task-switch task, which tests the unconscious, rapid shifting between two tasks such as pressing two computer keys, one corresponding to a shape presented and the other key for a color presented. Moreover, the 24 hour urinary polyphenol metabolite excretion increased significantly in the wild blueberry group. Primary metabolites present included pyrogallol-O-sulfate, 2 methylpyrogallol-O-sulfate, 4-methylcatechol-O-sulfate, 4-methylcatechol, and isoferulic acid. These findings illustrate that daily consumption of wild blueberry powder or consumed as intact blueberries, can improve cognitive performance and vascular function as well as decreasing blood pressure in healthy, older individuals presumably due to the berries’ high content of flavonoid polyphenols. Furthermore, the enhanced cognitive performance with wild blueberry supplementation suggests that an older population at risk for cognitive decline can improve episodic memory processes and executive function by lifestyle modifications involving increased berry consumption.
Most of the health promoting benefits of blueberries come from their abundant content of the polyphenol anthocyanin, which also contribute to their vibrant blue pigment. Polyphenols are plant derived molecules that include flavonoids, anthocyanins, ellagitannins, and quercetin. These large molecules although structurally varied, are all poorly absorbed by the small intestine (less than 5%), making their way into the end of the small and large intestine, where they are broken down into multiple metabolites by gut metabolites. These breakdown products are not only essential nutrients for the microbes (prebiotics) and improve the health of the microbial ecosystem but when absorbed, exert powerful health promoting effects on the gut, the brain and cardiovascular system..
In summary, a number of controlled studies depict that the addition of polyphenol and fiber-rich berries, especially wild blueberries, can serve as a natural and alternative means to decreasing one’s risk for developing CVD and premature cognitive decline. The addition of fresh and freeze-dried blueberries to one’s diet provide relatively the same amount of anthocyanin, even though consuming fresh berries provides a higher vitamin-C.
Chloe Arzy is a recent graduate from the University of Southern California where she earned her Bachelor of Science in Business Administration. She complemented her studies by receiving her Integrative Nutrition Health Coach certification from the Institute of Integrative Nutrition (IIN). She enjoys volunteering at Cedars Sinai Medical Center in the Advanced Heart Failure unit.