The term ‘superfood’ seems to be everywhere in the health space at the moment. To be honest, I often think this term is used as a marketing tool. One food that is claimed to be a so-called ‘superfood’ is the blueberry. So what actually makes blueberries a ‘superfood’? Is there any scientific merit to this claim? Naturally as a scientist, I decided to conduct my own research on the topic using credible, peer-reviewed studies.
Berries, including blueberries, do contain a large amount of vitamins A, C and E and B complex vitamins. Blueberries are high in β-carotene, which is the precursor to vitamin A (1).
According to a recent review in the journal Nutrition, blueberries contain 15-35mg/100g of calcium, 6-10mg/100mg of magnesium, 0.15-0.60mg/100g of iron, 56-80mg/100g of potassium and 0.06-0.012mg/100g of zinc (1). How does this compare to other common fruits? According to the Australian Food, Supplement and Nutrient Database (AUSNUT) for 2011 – 13, compiled by Food Standards Australia New Zealand, apricots contain 16mg/100g of calcium and oranges contain 32mg/100g of calcium, bananas contain 31mg/100g of magnesium, oranges contain 0.4mg/100g of iron, kiwifruit contain 28mg/100g of phosphorus and bananas contain 346mg/100g of potassium. And what about broccoli? Broccoli contains 32mg/100g of calcium, 21mg/100g of magnesium, 0.84mg/100g of iron and 0.mg/100g of zinc. So blueberries are comparable to other fruits and vegetables in terms of minerals.
There has been increasing interest in polyphenols in the past 10 years due to their antioxidant properties, abundance in the human diet and their likely role in the prevention of a range of diseases associated with oxidative stress, such as cancer and cardiovascular and neurodegenerative disease (2).
The polyphenols are classified into the following groups based on their structure: phenolic acids, flavonoids, stilbenes and lignans. This seems to be the feature of blueberries that makes them stand out from other fruits and vegetables.
Blueberries are one of the fruits containing the highest content of the phenolic acid hydroxycinnamic acid with 200-220 mg/100g of fresh fruit. Kiwi fruit in comparison contains 60-100mg/100g of hydroxycinnamic acid (3, 4). Blueberries are also a rich source of flavonols (the most abundant flavonoids in food) behind onions, kale, leeks and broccoli (5). Blueberries are also relatively abundant in the flavonoid anthocyanin, along with blackberries, black currants and rhubarb (6).
The polyphenol content of food can vary quite considerably due to environmental factors (soil type, sun exposure and rainfall), ripeness and storage conditions. Peeling, cooking and industrial processing can massively reduce the polyphenol content in fruit and vegetables (7). While this would not apply to fresh blueberries, I wondered what the freezing process would do to the polyphenols, particularly the anthocyanins, present in blueberries. I came across a study entitled ‘The Change of Total Anthocyanins in Blueberries and Their Antioxidant Effect After Drying and Freezing’. This study found no significant decrease in anthocyanin levels in blueberries frozen for three months compared to fresh berries and found no significant decrease in antioxidant activity between fresh, dried and frozen blueberries (8).
For this section, I limited my search to studies published in the highest ranked peer-reviewed journal in nutrition and dietetics, The American Journal of Clinical Nutrition (AJCN). AJCN has been in publication since 1952 and publishes the latest findings in basic and clinical studies relevant to human nutrition.
One study looked at the effects of blueberry consumption on cardiovascular health. In this study, 21 healthy men were given a blueberry drink containing known amounts of polyphenols. The researchers found that 1-2 hours after consumption of the blueberry drink, an increase in vasodilation of the brachial artery (the major blood vessel of the upper arm) was observed. A second increase was observed at 6 hours after consumption. Increases in the concentration of polyphenol metabolites in plasma were also observed 1-2 hours and 6 hours after consumption of the blueberry drink. This improvement in endothelial function may have been due to the inhibition of the enzyme NAPDH oxidase by the phenolic metabolites, which resulted in an increase in nitric oxide (9). Nitric oxide is a known vasodilator. This study was conducted over a short time period and the authors admit that these findings offer limited predictions for the longer-term consumption of blueberry polyphenols on vascular health.
A study published in 2012 in AJCN attempted to associate the consumption of flavonoid rich foods with the risk of type 2 diabetes in US men and women (10). Data from 3 different cohorts consisting of 70 359 women from the Nurses’ Health study (1984-2008), 89 201 women from the Nurses’ Health Study II (1991-2007) and 41 334 men from the Health Professionals Follow Up Study (1986-2006) were included in this analysis. The study found that the consumption of foods rich in anthocyanins, including blueberries, were associated with a significantly lower risk of type 2 diabetes. While this study provides correlation and not causation, it has been shown that anthocyanins can significantly decrease blood glucose concentrations and improve insulin sensitivity in a mouse model for type 2 diabetes (11).
I will mention one more study, which looked at the effect of 8 weeks of berry consumption (2 portions of berries daily) on blood pressure, plasma lipids and platelet function in 72 male and female volunteers. The researchers found that the consumption of berries for 2 months reduced systolic blood pressure, increased HDL-cholesterol concentrations (that’s a good thing) and had favourable changes on platelet function (12).
Perhaps I have been a bit harsh on the blueberry. With the abundance of vitamins, minerals and polyphenol compounds combined with some positive results from human studies and with only 57 calories per 100g maybe blueberries really are a superfood. So if you are going to eat fruit, then blueberries are a good choice. Try them in this brownie.
1/3 cup coconut flour
1 teaspoon baking powder
½ cup almonds
1 teaspoon cinnamon
½ cup dates soaked in ½ cup hot water
1 cup coconut milk
4 tablespoons cocoa powder
1 tablespoon granulated stevia
1 teaspoon vanilla extract
1 tablespoon coconut oil
½ cup frozen blueberries
- Add the almonds to a food processor and process until they resemble the texture of coarse crumbs. Pour the processed almonds into a large mixing bowl.
- Add the coconut flour, baking powder and cinnamon and mix to combine.
- Add the dates, plus the water they were soaked in, into the food processor along with the coconut milk, cocoa powder, stevia, vanilla extract and coconut oil. Process until the dates are pulverized.
- Add the blueberries and process for about 5 seconds – just long enough to mix the blueberries and chop them slightly, but still leave them chunky.
- Add the date mixture to the dry ingredients and mix well to combine. Add the egg and mix well.
- Pour the brownie mixture into a 20cm x 20cm baking tray lined with baking paper.
- Bake in the oven at 160°C for 40 minutes. Allow to cool completely before topping with icing (recipe below).
Blueberry cinnamon icing
¼ cup blueberries
¼ cup ricotta cheese
¼ cup Greek yoghurt
1 scoop of a good quality vanilla whey protein powder
½ teaspoon cinnamon
1 teaspoon gelatin dissolved in 2 tablespoons boiling water
- Add the blueberries, ricotta cheese, Greek yoghurt, whey protein powder and cinnamon to a food processor.
- Process to combine. Pour this mixture into a mixing bowl.
- In a separate small bowl, dissolve the gelatin in the boiling water. Add the gelatin to the icing mixture and stir well. Allow the icing to set in the fridge, stirring periodically to prevent clumping.
- Nile, S. and Park, S. (2014). Edible berries: Bioactive components and their effect on human health. Nutrition. 30:134-144.
- Scalbert, A., Manach, C., Morand, C., Rémésy, C. and Jime´nez, L. (2005). Dietary Polyphenols and the Prevention of Diseases. Crit Rev Food Sci Nutr. 45: 287-306.
- Shahidi, F. and Naczk, M. (1995). Food phenolics, sources, chemistry, effects, applications. Lancaster, PA: Technomic Publishing Co Inc.
- Clifford, M. (1999). Chlorogenic acids and other cinnamates—nature, occurrence and dietary burden. J Sci Food Agric. 79:362–72.
- Justesen, U., Knuthsen, P., Leth, T. (1998). Quantitative analysis of flavonols, flavones, and flavanones in fruits, vegetables and beverages by high performance liquid chromatography with photo-diode array and mass spectrometric detection. J Chromatogr A. 799:101–10.
- Mazza, G. and Maniati, E. (1993). Anthocyanins in fruits, vegetables, and grains. Boca Raton, FL: CRC Press.
- Crozier, A., Lean, M., McDonald, M. S. and Black, C. (1997). Quantitative analysis of the flavonoid content of commercial tomatoes, onions, lettuce, and celery. J Agric Food Chem. 45:590–5.
- Lohachoompol, V., Srzednicki, G., & Craske, J. (2004). The Change of Total Anthocyanins in Blueberries and Their Antioxidant Effect After Drying and Freezing. Journal of Biomedicine and Biotechnology. 2004: 248–252.
- Rodriguez-Mateos, A., Rendeiro, C., Bergillos-Meca, T., Tabatabaee, S., George, T., Heiss, C. and Spencer, J. (2013). Intake and time dependence of blueberry flavonoid–induced improvements in vascular function: a randomized, controlled, double-blind, crossover intervention study with mechanistic insights into biological activity. Am J Clin Nutr. 98: 5 1179-1191.
- Wedick, N., Pan, A., Cassidy, A., Rimm, E., Sampson, L., Rosner, B., Willett, W., Hu, F., Sun, Q. and van Dam, R. (2012). Dietary flavonoid intakes and risk of type 2 diabetes in US men and women. Am J Clin Nutr. 95: 4 925-933.
- Sasaki, R., Nishimura, N., Hoshino, H., Isa, Y., Kadowaki, M., Ichi, T., Tanaka, A., Nishiumi, S., Fukuda, I., Ashida, H., Horio, F. and Tsuda, T. (2007). Cyanidin 3-glucoside ameliorates hyperglycemia and insulin sensitivity due to downregulation of retinol binding protein 4 expression in diabetic mice. Biochemical Pharmacology. 74: 1619-1627
- Erlund, I., Koli, R., Alfthan, G., JMarniemi, J., Puukka, P., Mustonen, P., Mattila, P. and Jula, A. (2008). Favorable effects of berry consumption on platelet function, blood pressure, and HDL cholesterol. Am J Clin Nutr. 87: 2 323-331.