Blueberry

Background:

Diets with high amounts of fruits and vegetables have been associated with a decreased risk of developing depression. This is thought to be due to the high flavonoid content found in plants.

Flavonoids are phytonutrients, meaning nutrients found in plants. There are over 6,000 types, and different types have different health benefits.

Blueberries contain many flavonoids and of their various phytochemicals, anthocyanins probably have the greatest health effects. Blueberries are thought to be one of the greatest antioxidants of all common fruits and vegetables.

Blueberries are native to North America, but are not grown around the world.

Mechanism of action:

Pro-cognitive effects: Flavonoid consumption is associated with vascular and cognitive benefits. Increasing blood flow to the brain and improving brain functioning can both be helpful in treating depression.

Antioxidant effects: The antioxidant effects of blueberries protects the brain against neuronal stress.

Anti-inflammatory effects: Depression is often associated with a chronic, low-grade inflammation in the brain and people with depression often have higher levels of inflammation markers. Decreasing inflammation can help the brain to function properly and help treat depression.

Dosing:

The studies used a freeze-dried blueberry powder that was equivalent to one cup of blueberries daily. Another study used 10 mg of blueberry extract daily.

Effectiveness:

One study looked at the short-term effects of blueberry consumption on mood. The participants in the trial included 21 young adults age 18-21 and 50 children age 7-10 years old. The participants where given a mood questionnaire to assess their baseline, then given a blueberry drink or a placebo drink (matched with the same amount of vitamin C and sugar as the blueberry drink) and then given the mood questionnaire two hours later. Interestingly, the positive affect scores improved in the blueberry group but not in the placebo group. The positive affect scores included measures such as joyfulness and liveliness. ¹

A second study had similar protocols to the first trial, but looked at longer term effects by having the 64 participants (age 12-17) consume the blueberry product daily for four weeks. This study showed the blueberry group had less symptoms of depression compared to the placebo group at the conclusion of the four weeks. ²

A study of 124 patients aimed to determine if blueberry would decrease cerebral venous thrombosis (CVT) induced mild to moderate depression. CVT is a clot in the cerebral vein in the brain and is associated with depression. Participants either received 10 mg of blueberry extract daily or placebo daily. After three months, the blueberry group had their depression symptoms lessened by 48.7% and had 83.9% less gastrointestinal infections. Brain derived neurotropic factor (BDNF), which can be thought of as fertilizer for brain cells was increased in the blueberry group. ³

Safety:

No adverse effects have been reported in clinical trials. Blueberries do contain sugar and could increase blood sugar and high fruit consumption can contribute to cavities.

Other:

There is also some evidence that shows potential cognitive improvements after blueberry consumption.

One study had 35 participants age 40-65. The participants attended two sessions. They consumed blueberry in one session and a matched placebo in another session and then completed cognitive sessions. The blueberry group did better in demanding tasks and had less cognitive fatigue. ⁴

References:

1. Khalid S, Barfoot KL, May G, et al. Effects of acute blueberry flavonoids on mood in children and young adults.Nutrients. 2017;9(2):158.
2. Fisk J, Khalid S, Reynolds SA, Williams CM. Effect of 4 weeks daily wild blueberry supplementation on symptoms of depression in adolescents.Br J Nutr. 2020;10:1-8.
3. Xu N, Meng H, Liu T, Feng Y, Qi Y, Zhang D, Wang H. Blueberry phenolics reduce gastrointestinal infection in patients with cerebral venous thrombosis by improving depressant-induced autoimmune disorder via miR-155-mediated brain-derived neurotrophic factor. Front Pharmacol 2017;8:853.
4. Whyte A, Rahman S, Bell L, et al. Improved metabolic function and cognitive performance in middle-aged adults following a single dose of wild blueberry. Eur J Nutr 2021 Apr;60(3):1521-1536.