Green tea extract and white blood cell activity in 20 people
What it found
Taking green tea extract for 14 days increased the response of white blood cells and raised antioxidant levels in the blood of 20 healthy people.
These changes returned to normal after four weeks off the supplement.
What they found
Studies in people
White blood cell response
After 14 days, stimulated white blood cells released more myeloperoxidase and lactoferrin, two proteins involved in fighting bacteria. For some people the release roughly doubled, but 15% of subjects showed no increase at all.
Blood antioxidant levels
The ability of the blood to neutralise free radicals rose significantly after 14 days of taking the extract. Three people saw no change in this measure.
White blood cell counts
Total white blood cell numbers dipped slightly during the trial, with one person dropping by 30%. All counts stayed within the normal range of 4 to 11 x 10^9/L for healthy adults.
Effects faded after stopping
Four weeks after volunteers stopped taking the extract, protein release, antioxidant levels and cell counts all returned to where they started on day 0.
What the authors conclude
- They conclude that taking green tea extract as a supplement for 14 days can boost white blood cell activity and raise antioxidant levels in the blood.
- They suggest this might help the body respond better to bacterial infections while the supplement is being taken.
- They note that more work is needed to identify which parts of the extract cause these effects.
How it was done
White blood cells help defend the body against infections, and green tea contains compounds known to reduce inflammation. The authors wanted to see if a green tea extract could boost white blood cell function in people.
Ten men and ten women aged 20 to 55 took three pills daily, providing 300 mg of green tea extract, for 14 days. Blood samples were taken before starting, after 14 days, and again after a four-week break from the pills. Their usual diet and lifestyle stayed the same throughout.
What it can’t tell you
- This trial lasted only 14 days, so it cannot show what happens when people take green tea extract for months or years.
- It measured lab markers of immune response rather than tracking actual infections, so it cannot prove whether people got sick less often.
- With only 20 volunteers, the results may not apply to everyone.
The paper
- Title
- Dietary supplementation with green tea extract promotes enhanced human leukocyte activity
- Type
- Clinical trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Lowe GM, Gana K, Rahman K (2015). Dietary supplementation with green tea extract promotes enhanced human leukocyte activity. Journal of complementary & integrative medicine. doi:10.1515/jcim-2014-0042Free full textPubMed 26259232DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error