Background: Since homocysteine (Hcy) is a risk factor for cardiovascular and other diseases, it is important to know how exercise can modify it. Previous studies have suggested that endurance training influences Hcy. However, little is known about the effect of training intensity on Hcy. Materials and Methods: We investigated Hcy, vitamin B12, vitamin B6, folate and methylmalonic acid (MMA) before and after 3 weeks of volume-oriented training (VOL) (30 km/week) and high-intensity interval training (HIT) (20 km/week) in 20 young swimmers (16±2 years). Afterward, the athletes completed 5 days of recovery training. Results: The training induced a Hcy increase in HIT and VOL (6.47±0.95 μmol/l vs. 7.44±1.17 μmol/l and 7.33± 1.92 μmol/l vs. 8.28±1.42 μmol/l, respectively) that persisted during the recovery period (8.02±1.69 μmol/and 8.00±1.81 μmol/l, respectively). Vitamin B12 was unchanged after the training (539±166 ng/l vs. 556±192 ng/l and 480±144 ng/l vs. 491±124 ng/l, respectively) but decreased during the recovery period (459±134 ng/l and 451±116 ng/l, respectively). Folate showed an increase during the training (9.07±2.01 μg/vs. 11.71±4.08 μg/l and 10.34±2.32 μg/l vs. 11.13± 4.64 μg/l, respectively), which was reversible by the end of the recovery training (8.57±1.98 μg/l and 9.60±2.38 μg/l, respectively). Vitamin B6 and MMA did not change. For none of the measured parameters were there significant differences between HIT and VOL. Conclusion: Three weeks of strenuous swimming caused a prolonged Hcy increase, which was accompanied by changes in vitamin B12 and folate. The magnitude of these effects was not influenced by the training intensity.
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