Effect of blueberry ingestion on natural killer cell counts, oxidative stress, and inflammation prior to and after 2.5 h of running.
Journal Title (Medline/Pubmed accepted abbreviation):  Appl. Physiol. Nutr. Metab.
Year: 2011
Volume: 36
Page numbers: 976-984

Summary of background and research design:

Background: Reactive oxygen species are compounds that are involved in the development of many chronic diseases including cancer. Frequent intake of antioxidants, such as those found in blueberries, may help combat oxidative stress and place the body in an overall healthier state. Exercise, although it promotes oxidative stress to some degree, also induces the body's natural defenses to better cope with oxidative stressors encountered in everyday life.

Natural killer cells (NK cells)- these are immune cells, most commonly recognized to fight against cancer cells. In this case, the higher the number, the better.

Hypothesis: Six weeks of 250 g blueberries/day will lead to better control of exercise-induced oxidative stress.

Subjects: 25 well-trained participants, age ~20-40 yrs old

Experimental Design: randomized, parallel group

Procedure: About 1 week before the start of the study, the participants were familiarized with the exercise procedures and the VO2max was determined. The blueberry group was provided blueberries that they were encouraged to incorporate into their diet at 250 g/day. The control group followed their normal diets. After 6 weeks, the participants reported to the laboratory fasted in the morning. They ran on the treadmill for 2.5 hrs at ~72% their previously determined VO2max. The blueberry group consumed 375 g blueberries after the baseline blood draw and muscle biopsy. Additional blood samples and muscle biopsies were acquired immediately after exercise, and 1 hr post-workout. During the study, all participants followed a diet composed of foods from a dietitian's list (certain foods high in vitamins C and E were avoided). Blood was subjected to a battery of tests that assessed oxidative stress and activation of the immune system including: F2 isoproastanes (marker of oxidative stress), oxidative nucleic bases (sign of oxidative stress), ferric reducing antioxidant potential (FRAP, measure of antioxidant capacity), homocysteine, inflammatory cytokines, lymphocyte subset (white blood cells, provides information regarding inflammation), and others.

Summary of research findings:
  • Blueberries did not enhance performance.
  • F2-isoprostanes increased 129% from baseline to immediately post-exercise in the control group and only 55% in the blueberry group.
  • From pre-exercise to 1 hr post-exercise, cortisol concentration decreased 10% in the blueberry group and 23% in the control group.
  • NF-κB increased from baseline to post-workout similarly in both groups.
  • One RNA base marker showed a decrease in modification in the blueberry group and not the control group but there was no change in the DNA marker.
  • Inflammatory cytokines IL-10, IL-1ra, IL-6, and IL-8 all increased after exercise with no difference between groups.
  • The lymphocyte proliferation response decreased post-exercise for both groups to a similar extent.
  • Natural killer cells were elevated almost 2-fold before exercise and remained elevated after exercise. The blueberry treatment tended to be associated with increased levels of natural killers cells compared with control.

Key practice applications:

Daily consumption of blueberries for 6 wks led to an increase in immunity and a decrease in exercise-induced oxidative stress. One components of the blueberries that may have led to these health benefits is antioxidants including flavonoids (anthocyanins, specifically).


  • Vitamins C and E were avoided for 6 weeks. It is unknown if the control group showed higher signs of oxidative stress because the diet was insufficient in these nutrients.
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