**5. Conclusions**

Our study indicated that a 2 weeks supplementation of 1.25 g of betaine mixed with 300 mL of sports beverage twice per day significantly increased the plasma betaine concentration and effectively attenuated lymphocyte apoptosis after EEE. However, betaine supplementation had no effects on MTP decline, oxidative stress (TBARS and PC), or aerobic capacity (time to exhaustion, VO2max, HRmax, and AHR). This study provides a nutritional supplementation strategy to attenuate exercise-induced lymphocyte apoptosis for intensive training athletes. Athletes may have better physiological status to conduct the training and shorten the recovery time during long term training periods. We recommend future studies use a higher dosage (more than 3 g, but less than 6 g per day) of betaine or combine it with other nutritional supplements to evaluate the effects of betaine supplementation on other athletic performance parameters or other related biomarkers of apoptosis.

**Author Contributions:** Formal analysis, M.-T.Y. and K.-H.C.; Investigation, M.-T.Y., X.-X.L., B.-H.H., L.-H.C., and C.-C.W.; Methodology, M.-T.Y. and K.-H.C.; Project administration, K.-H.C.; Writing-original draft, M.-T.Y., X.-X.L. and K.-H.C.; Writing-review and editing, M.-T.Y. and K.-H.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by the Ministry of Science and Technology (MOST) of the Executive Yuan, Taiwan, under grant No. NSC 102-2410-H-179-002.

**Acknowledgments:** The authors are grateful to all participants who completed the study and the anonymous reviewers who aided in manuscript preparation. The authors also wish to thank Kuan-Wei Lee for the assistance with biochemical analysis and the Core Facility Center of Taipei Medical University for performing the liquid chromatography–mass spectrometry analysis.

**Conflicts of Interest:** The authors declare no conflict of interests.
