Blueberries contain high levels of micronutrients and antioxidant anthocyanins. Anthocyanins help protect plants from excessive radiation and infectious pathogens, and the characteristics of helping blueberries survive better also bring benefits to human beings, such as reducing inflammation, improving metabolic function and enhancing energy production in cells.
In the United States, about 50% people develop insulin resistance around middle age, which usually leads to a disease called "pre-diabetes". Researchers recruited 33 pre-diabetic patients aged 50-65 from around Cincinnati. These patients are overweight and their memory declines slightly with age. During 12 weeks, participants were asked to abstain from any kind of berry fruit except a bag of supplementary powder that can be mixed with water for breakfast or dinner every day. Half of the participants received the powder equivalent to half a cup of whole blueberries, while the other half received a placebo. The researchers also tested the decline level of some cognitive abilities of the participants, such as working memory, psychological flexibility and self-control.
The results showed that people in blueberry treatment group showed improvement in cognitive tasks that depended on executive control, and significantly reduced the interference of external information in learning and memory. In addition, patients in the blueberry group also have lower fasting insulin levels, which means that the metabolic function of participants has been improved and they can burn fat more easily to obtain energy.
The blueberry group showed a slightly higher degree of mitochondrial uncoupling, which is a cellular process related to longer life span and reduced oxidative stress. Oxidative stress can lead to fatigue and memory loss. The main conclusion of this study is that regular supplementation of blueberries in the diet of middle-aged people at risk of Alzheimer's disease may reduce their chances of getting sick.