Blueberries - Healthy Benefits Through Anthocyanins
Blueberries, which belong to the heath family, are closely related to cranberries. Due to their rich variety of ingredients and bioactive compounds, they are often referred to as superfood, superfruit, or functional food in the literature 1 2 3 4. The bioactive compounds primarily include secondary plant substances such as phenolic acids and flavonoids, as well as vitamins like vitamin C and minerals with antioxidant benefits. They are responsible for a range of benefits on health.
The healthy blueberries grow either on small flowering bushes or low on the forest floor as wild species. The fresh blueberries available in the market are derived from cultivations of the American blueberry (Vaccinium corybosum). The main cultivation areas are in Europe and North America 5. During the ripening process, the berries change their color from green to blue-purple. During the season, from early June to August, cultivated blueberries are available for purchase in fresh form.
Differences between Blueberries and Bilberries
Wild blueberries (Vaccinium myrtillus) contain 3 times more secondary plant compounds than cultivated half-shrubs 6 7. They are significantly smaller than cultivated blueberries. They grow to a maximum size of 1 cm and are much smaller than cultivated blueberries. The flesh is red-blue. They are usually available for purchase as preserved in glass jars. The fruit itself is also softer and juicier compared to cultivated blueberries.
Cultivated half-shrubs can grow up to 4 meters tall. These bilberries are also referred to as blueberries. They can reach a diameter of 2 cm. The flesh is white to slightly greenish. They are mostly sold fresh in the produce section and frozen in the frozen foods aisle.
Calories in Blueberries
Blueberries consist mainly of water (84%). Accordingly, their calorie content is very low at 57 kcal per 100 g. The majority of the calories come from carbohydrates, totaling 14.49 g. Among those, 4.97 g is fructose and 4.88 g is glucose. Compared to other fruits, they have relatively low sugar content.
Blueberries contain protein and fat in very small amounts, with 0.74 g and 0.33 g, respectively.
With a fiber content of 2.4g, blueberries are in the midfield of the fiber-rich fruits. Fiber cannot be digested by the body. It serves as a source of nourishment for intestinal bacteria, contributing to a healthy gut flora.
Minerals and Vitamins
Blueberries are also a good source of vitamin C (9.7mg) and vitamin K1 (19.3µg). They also contain bioactive carotenoids in very high concentrations, with 2,140μg/100g in the healthy berries. 8 9. Carotenoids are primarily used as provitamin A for the body's own production of vitamin A.
For more nutritional values of blueberries, click here.
Health Benefits of Antioxidants
Many scientific studies confirm that blueberries have one of the highest antioxidant capacities among all fruits. 10 11 12 13. The antioxidant capacity of a food expresses its ability to scavenge free radicals and deactivate oxygen radicals. Rutin, cyanidin, myricetin, syringic acid, and chlorogenic acid exhibit the highest antioxidant capacity 14 15 16 17 18. Chlorogenic acid is the most abundant phenolic acid (tannin) in the healthy blueberries 19 20.
So protect the body from aggressive free radicals. These radicals can cause cell damage and lead to cancer. 27 Antioxidant compounds may also help reduce the occurrence of cancer, cardiovascular diseases, neurodegenerative diseases, DNA damage, and aging processes. 28 DNA damage can trigger cancer and other diseases. 29 Additionally, DNA damage negatively affects aging in the body.
In addition, blueberry antioxidants protect red blood cells (erythrocytes). 30
The majority of antioxidants found in blueberries belong to the group of flavonoids, which are classified as polyphenols. Flavonoids have health benefits for the vascular system and the brain. 31 One group of flavonoids stands out – anthocyanins. They are responsible for the blue color of the fruits.
Fresh cultivated blueberries contain up to 438 mg of anthocyanins per 100 g (2,762 mg dry weight), and wild blueberries contain up to 1,017 mg (7,465 mg dry weight) 37. The most valuable part of cultivated blueberries for health is the skin, as it contains nearly all the anthocyanins 38.
Study results have shown that anthocyanins reach the intestine, are well absorbed by the body, and increase the antioxidant level in the body 39 40 41 42. Overall, the polyphenols are thoroughly metabolized by enzymes and intestinal flora 43. The anthocyanins pass through the blood-brain barrier into the organs and the brain 44. Out of 25 anthocyanins, 19 were detected in the blood 45. These compounds are of great benefit to health as natural antioxidants.
Anthocyanins in berry fruits trigger genetic messaging that promotes human health and prevents diseases 46. Anthocyanins improve neural and cognitive functions of the brain, promote eye health, and protect DNA, ensuring cell survival 47 48.
Antioxidants in blueberries can neutralize free radicals by improving the cells' antioxidant defense. 49 50. This can help prevent DNA damage. In a 6-week study, daily consumption of a glass of wild blueberry juice reduced oxidative DNA damage by 12.5% to 9.6% 51. Another study with 168 participants over four weeks showed that daily consumption of an apple-blueberry beverage reduced oxidative DNA damage by 20% 52 53.
Blueberries Protect Cholesterol from Oxidation
In addition, the antioxidants found in blueberries also protect cholesterol from oxidative damage. A study involving 14 participants showed that consuming 75g of blueberries significantly protects lipoproteins from oxidative damage 55. Lipoproteins are responsible for transporting fats like cholesterol in the blood.
In a further study, the reduced oxidation of LDL cholesterol was observed with blueberries. 56. LDL cholesterol (LDL = Low-Density Lipoprotein) is the "bad" cholesterol associated with several heart diseases.
Blueberries Improve Insulin Sensitivity
Study findings suggest that blueberries also have an antidiabetic benefit. 57. Thus, anthocyanins have a positive impact on insulin sensitivity and blood sugar metabolism.
Even twice-daily consumption of blueberry smoothies contributed to a significant improvement in insulin sensitivity among 15 overweight, non-diabetic, and insulin-resistant study participants. 58.
In a study involving subjects with metabolic syndrome, insulin sensitivity was not affected by daily consumption of blueberries. 59.
Blueberries have a glycemic index of 53 and a glycemic load of 5. 60. Thus, blueberries result in very minimal blood sugar spikes.
Anti-inflammatory and Pain-relieving Benefits
Flavonoids exhibit a wide range of biological activities, which include anti-inflammatory properties 63. Thus, blueberry powder suppresses the production of pro-inflammatory mediators such as IL-1β and IL-6 64.
In a further study, especially wild blueberries showed anti-inflammatory activities 65 66 67. The contained polyphenols and flavonoids (especially quercetin, epicatechin, and resveratrol) inhibit the activation of NF-κB (nuclear factor 'kappa-light-chain-enhancer' of activated B-cells) and the formation of inflammation-promoting cytokines such as TNF-α and IL-6. NF-κB controls gene expressions involved in inflammatory reactions.
In addition, in runners who consumed 375g of blueberries one hour before training, inflammatory markers and oxidative stress, which occur during physical activities, were reduced 68.
Due to the pain and inflammation-reducing activities of blueberries, their consumption could be helpful in the treatment of inflammatory diseases 69.
Blueberries also demonstrate a clear therapeutic potential in ulcerative colitis (chronic inflammatory bowel disease) 70. Inflammatory markers decreased due to the anthocyanins.
Blueberry extracts also have antiproliferative activities (directed against tissue proliferation) against human liver cancer cells 71.
Blueberries contribute to muscle regeneration
In a small New Zealand study involving 10 female athletes, it was demonstrated that consuming a blueberry smoothie can contribute to muscle recovery after strenuous leg strength training 72. The participants consumed the drinks 5 and 10 hours before, as well as 12 and 36 hours after exercise-induced muscle damage. The results suggest that consuming blueberries aids in muscle repair and accelerates muscle regeneration.
Further findings indicate that blueberries, with their high content of malvidin, could alleviate muscle damage caused by oxidative stress 73.
Benefits Against Cancer
Blueberries prevent carcinogenesis by inhibiting the formation of inflammation-promoting molecules, oxidative stress, and body products derived from oxidative stress 74. The latter include DNA damage, inhibition of cancer cell proliferation, and increased apoptosis (cell death).
The anthocyanins and their metabolic intermediates have shown anti-cancer benefits on breast cancer cell lines in studies. 78 79. They inhibited cancer cell proliferation as well as the invasion of cancer cells into surrounding tissue.
In addition, anthocyanins promote the cell death of oral cancer cell lines. 80.
Blueberry juice has potential chemopreventive activity and could be helpful in preventing tumor development. 81.
Beneficial for the Skin
Blueberry extracts reduce oxidative stress in human skin cell lines induced by UVA radiation, thanks to their antioxidant properties 84. Additionally, they were able to reduce the DNA damage caused by UVA and UVB radiation. UVA radiation penetrates deep into the skin and can be a cause of skin cancer.
Fighting Periodontitis and Gingivitis with Blueberries
Blueberry extracts, which are rich in flavonoids, have shown antibacterial activities against bacteria (Fusobacterium nucleatum) that cause periodontitis (inflammation of the gum tissue surrounding the roots of teeth) 85. The formation of bacterial biofilms (slimy films in which microorganisms colonize) could be inhibited by 87.5%. Furthermore, a pre-treatment of phagocytes with the extracts achieved an anti-inflammatory benefit.
Additionally, there is evidence that consuming 500g of blueberries reduces inflammation in gingivitis (bacterial-induced gum inflammation) to a similar extent as a standard treatment 86.
Improving Cognitive Function with Blueberries?
Scientists generally believe that a flavonoid-rich diet can positively influence cognitive development 87. Blueberries can protect the brain through their antioxidant and anti-inflammatory compounds, thereby reducing motor deficits as well 88.
So, the cognitive performance of 7- to 10-year-old children improved with the consumption of a powder made from freeze-dried wild blueberries, which was mixed into a beverage. 89 The best results were achieved with 30g of blueberry powder.
Blueberries may potentially protect against age-related deficits in cognitive and motor functions. 90 The scientists attribute these speculations to the ability of blueberries to reduce oxidative stress and inflammation or through direct modulation of neuronal communication.
Other researchers associate higher consumption of blueberries and strawberries in individuals over 70 years old with reduced cognitive decline. 91 The results suggest that cognitive aging can be delayed by 2.5 years.
Other scientists suggest an increased neural signal transmission in brain centers caused by anthocyanins, which can alleviate neurodegeneration. In this context, nine elderly individuals with a higher risk of dementia were provided with blueberry juice daily for 12 weeks 92. The result was a neurocognitive benefit, as the juice improved memory functions.
In a 7-day study involving 14 schoolchildren, the cognitive benefit of flavonoid-rich blueberry beverages was assessed 93. Significant improvements in memory retention were achieved with the beverage. The children remembered the words they had memorized earlier at a slower rate compared to the control group. However, there were negative effects when decoding words in groups with new words.
The anthocyanins contained in blueberries accelerate the recovery of visual acuity after retinal bleaching (fading of retinal pigments) 94. It is still unclear whether anthocyanins also have an impact on vision.
In addition, blueberries appear to limit or prevent eye diseases caused by oxidative stress through their antioxidant benefit 95. Thus, blueberries protect retinal cells from damaging influences.
Anthocyanin extracts are also beneficial for the health of the retinal pigment epithelium (outermost layer of the retina) 96. The extracts are capable of protecting cells from light-induced damage. This is achieved by suppressing cell aging and death and downregulating vascular endothelial growth factor (VEGF) to a normal level. Additionally, there is evidence that blueberry extracts can be helpful in the homeostasis and renewal of retinal cells.
Blueberries offer potential benefits for surface eye diseases such as dry eyes, thanks to their natural compounds (particularly pterostilbene) 97. Pterostilbene protects the cornea from inflammation and oxidative stress caused by hyperosmolarity (improper composition of tears).
Blueberries Can Lower Blood Pressure
Over a period of eight weeks, overweight individuals suffering from metabolic syndrome (a risk factor for heart disease) were able to lower their blood pressure by consuming 50 g of freeze-dried blueberries daily, equivalent to 350 g of fresh blueberries. 98. The systolic blood pressure decreased by 6% and the diastolic blood pressure by 4%. High blood pressure can be the cause of heart attacks and strokes.
In another study, the use of blueberry powder also demonstrated a blood pressure-lowering benefit 99. Over a period of eight weeks, researchers administered 22 grams of freeze-dried blueberry powder (equivalent to one cup of blueberries) to postmenopausal women with pre-hypertension and stage 1 hypertension. The participants were able to reduce their systolic blood pressure by 5.1% and diastolic blood pressure by 6.3%. Additionally, a 6.5% reduction in arterial stiffness was achieved. The researchers now speculate that daily consumption of blueberries could lead to improvements in blood pressure and arterial stiffness. These results may be attributed to the increased production of nitric oxide (+68.5%), which is involved in the dilation of blood vessels 100. Arterial stiffness and narrowing of blood vessels are causes of hypertension and therefore responsible for an increased risk of cardiovascular diseases.
In other studies as well, the consumption of 250g of blueberries daily for six weeks has been shown to reduce diastolic blood pressure and arterial stiffness. 101.
Furthermore, blueberries significantly improve vascular function in healthy men. 102. This benefit is likely caused by circulating phenolic metabolites.
Other active components of blueberries, such as pterostilbene, may also help in the prevention of cardiovascular diseases associated with endothelial dysfunction. 103. The endothelium refers to the cells lining the inner wall of lymph and blood vessels.
Further study results also suggest that vascular and endothelial functions are improved with the consumption of blueberries. 104 105. However, no blood pressure-improving benefit was observed in subjects with metabolic syndrome. 106. However, a large portion of the study participants were taking antihypertensive medication.
A 2016 study summary demonstrates the blood pressure-lowering benefit of blueberries (systolic blood pressure: -0.28 mmHg; diastolic blood pressure: -0.5 mmHg) 107. However, the values do not show significant results, so the scientists do not attribute clinical efficacy to the healthy berries.
Blueberries for the Immune System
Runners who consumed 250g of blueberries per day for six weeks showed a higher proportion of natural killer cells 108. Natural killer cells are part of the immune system and eliminate old and degenerated cells.
In another study, the number of natural killer cells was also increased after 6 weeks of daily consumption of 250g of blueberries 109.
In addition, blueberry phenols have antimicrobial capabilities against certain bacteria genera 110 111 112. They can inhibit the proliferation of Salmonella, Listeria, Escherichia coli, and Staphylococci.
Furthermore, blueberry juices have the potential to act against pneumococcal infections 113. Pneumococci cause respiratory diseases.
Are Blueberries Good for the Bladder?
Consuming large amounts of blueberries can have a laxative effect.
In very rare cases, an allergy may occur 116.
Proper Storage of Blueberries
Processing (such as baking or juicing) and prolonged storage of blueberries lead to a loss of some beneficial secondary plant compounds 117 118 119 120 121 122. However, a significant portion of the bioactive compounds can be preserved through gentle processing, freezing, and storage at low temperatures. The optimal storage temperature is 0 °C 123.
Healthy blueberries are a great addition to muesli, fruit salads, green salads, yogurt, vegan pancakes, sorbets, muffins, crêpes, and waffles, thanks to their sweet taste. They also complement pseudocereals like quinoa and amaranth very well in terms of flavor.
In addition, blueberries are used to make jams and ice creams.