Exercise increases tryptophan availability to the brain in older men age 57-70 years.
Level 4 - case-series / case-control
Single-arm pre-post physiological study without a non-exercise control group
PubMed 22051569 · doi:10.1249/MSS.0b013e31823ede8e
What was done
Nineteen men aged 57–70 years (mean age 64 ± 3 yr) performed a 60-minute treadmill exercise session at ~68% of peak oxygen uptake (VO2peak). Fasting blood samples were drawn at rest (baseline), at 30 and 60 minutes of exercise, and at 90 minutes (30 minutes post-exercise). Researchers measured total and free tryptophan (TRP), branched-chain amino acids (BCAA), prolactin, nonesterified fatty acids (NEFA), ammonia, glucose, and lactate to evaluate peripheral proxies of central serotonin availability and synthesis.
What was found
The serum free TRP/BCAA ratio increased by 102% from baseline after 1 hour of exercise (P < 0.0001) and remained 78% above baseline at 90 minutes (P < 0.001). Serum free TRP rose from 2.8 ± 0.7 µmol·L⁻¹ at baseline to 5.7 ± 1.8 µmol·L⁻¹ at 1 hour (P < 0.001) and correlated strongly with plasma NEFA concentrations across all time points (r = 0.887, P < 0.0001). Serum prolactin increased significantly to 8.6 ± 2.4 µg·L⁻¹ after 1 hour (P < 0.001) and showed a moderate positive correlation with the free TRP/BCAA ratio (r = 0.48, P < 0.05).
Why it matters
This study confirms that acute moderate-intensity exercise elevates peripheral markers of brain tryptophan availability in older adults, mimicking responses observed in younger cohorts. It supports the mechanistic hypothesis that exercise-induced enhancements in central serotonergic pathway substrate availability may contribute to mood improvements in aging populations.
Limits
The study is limited by a small sample size (n = 19) consisting exclusively of older men, precluding generalization to women. There was no non-exercise resting control condition. Central serotonin synthesis and brain activity were not measured directly, relying entirely on circulating peripheral proxies (free TRP/BCAA ratio and prolactin), and no clinical mood or depressive symptom outcomes were assessed.
Cited by
- supports Exercise causes branched-chain amino acids to be taken up into muscle cells, reducing competition for tryptophan transport across the blood-brain barrier.