This paper is part of NMJ's 2018 Cognition and Mental Health Special Issue. Download the full issue here.

Reference

Nilsson A, Salo I, Plaza M, Björck I. Effects of a mixed berry beverage on cognitive functions and cardiometabolic risk markers; a randomized cross-over study in healthy older adults. PLoS One. 2017;12(11):e0188173.

Objective

To evaluate the effects on cognitive function and cardiometabolic risk markers from 5 weeks of consuming a drink made primarily from dark berries.

Design

Randomized crossover trial; 5-week intervention, 5-week wash-out, 5-week intervention

Participants

Forty healthy Swedish adults aged 50 to 70 (average age 63), 30 women and 10 men, normal to slightly overweight (average BMI≤28), all nonsmokers with no evidence of disease. All participants avoided alcohol, antibiotics, probiotics, and dietary intake of berries or high-fiber foods during the study period.

Intervention

Participants were randomized into either the BC group (n=20) or the CB group (n=20); the first 5 weeks the BC group consumed the berry drink while the CB group consumed the control drink. During the second 5-week intervention period (following a 5-week washout period), the BC group consumed the control drink and the CB group consumed the berry drink.

While I must admit that I was amazed to learn about the ability of berry pigments (anthocyanins) to improve insulin response, I was not at all surprised to read about their neurological impact.

During each 5-week intervention period participants consumed 600 mL of the berry drink or control drink per day (200 mL with each meal). The berry drink was made from 150 grams of frozen blueberries and 50 grams each of frozen black currants, elderberries, lingon berries, and strawberries, all combined with 6 grams of tomato powder (from 100 g of tomatoes). The control drink (water-based) was similar in carbohydrate content, volume, and pH.

Study Parameters Assessed

Participants were assessed 4 times during the study, first at baseline then again after each of the 5-week intervention segments. Working memory and selective attention were assessed with standard neurocognitive testing methods. Vital signs were recorded and blood was drawn and assessed for the following cardiometabolic risk markers: glucose, insulin, homeostatic model assessment of insulin resistance (HOMA-IR), free fatty acids (FFAs), cholesterol, interleukin (IL)-6, IL-18, malondialdehyde (MDA), and oxidized low-density lipoprotein (LDL).

Both study and control drinks were assessed for total phenolic content, antioxidant activity, carbohydrates, fiber, protein, fat, and pH.

Primary Outcome Measures

Changes in the above parameters (cardiometabolic risk markers and cognitive performance) following a 5-week consumption of the berry drink compared to 5-week consumption of the control drink.

Key Findings

Participants

Based on cardiometabolic risk markers, all except 7 of the 40 participants who completed the study had one or more of the common diagnostic components of metabolic syndrome, as defined by the International Diabetes Federation, at baseline.

Berry Drink Analysis

The berry drinks averaged 1,300 mg of polyphenols per liter and exhibited good antioxidant ability. The control drink had no polyphenols and no antioxidant activity. Both the control and berry beverages contained 2.2% glucose and 3.4% fructose. The berry beverage also had 0.6% protein, 0.3% fat, 1.35% insoluble fiber, and 0.45% soluble fiber compared to 0% of all of those for the control beverage.

Berry vs Control Group Comparison

Five weeks of 600 mL berry beverage per day reduced total and LDL cholesterol, insulin, and insulin resistance, while 5 weeks on the control beverage increased each of those markers. The differences for all of those 4 findings were statistically significant.

Working memory, 30 minutes postprandial, was better after 5 weeks of the berry drink than it was after 5 weeks of the control drink.

Practice Implications

This group of researchers included some very nice references about the association between both type 2 diabetes mellitus and metabolic syndrome and cognitive decline.1,2 Reduced cognitive function was actually found in some to precede changes in glucose tolerance.2,3 Previous studies also found that berries improved insulin sensitivity in obese adults and slowed the rate of cognitive decline in the elderly.4,5 While I must admit that I was amazed to learn about the ability of berry pigments (anthocyanins) to improve insulin response, I was not at all surprised to read about their neurological impact. Berry pigments are able to cross the blood-brain barrier and are highly effective at reducing neuroinflammation.6 These compounds are able to reduce nuclear factor-kappaB (NF-kB) levels in the brain.7

The researchers used frozen rather than fresh berries for the study drink. Bill Mitchell, ND, an early promoter of berry pigments, frequently said that freezing broke the cell walls and allowed more of the phenolic compounds to be available. While elderberries, black currants, and lingonberries are not readily available, frozen blueberries are. One can purchase a large bag of them at any Costco and every grocery store. While some individuals have been concerned that Environmental Working Group (EWG) has listed blueberries on the “dirty dozen” list, according to the Pesticide Data Program (where EWG gets their list) website, frozen blueberries failed to show the small amounts of residue found on fresh blueberries.8 I often recommend that individuals consume a cup of blueberries each day, yet this study may indicate that 3 cups may be better if it can be tolerated.

The researchers only used 2 of the many available neurocognitive testing methods and only found modest improvement in working memory after 5 weeks of the berry drink. Neurocognitive testing is readily available to clinicians for use in their office. It is a low-cost, quick, and easy-to-use test that provides a quantitative assessment of executive functioning. With this test clinicians could easily track patients’ cognitive improvement with naturopathic care.