Lymphocytes

When low (lymphopenia, <1.0 x10^9/L):

Common causes in athletes: Overtraining syndrome, severe caloric deficit (contest prep), chronic psychological stress, high-dose corticosteroids.

Supplements:

• Zinc -- 30mg/day (critical for T-cell development)
• Vitamin D3 -- 5000 IU/day (immune modulation)
• Glutamine -- 5-10g/day (immune cell fuel, especially during caloric deficit)
• Probiotics -- 10-20 billion CFU/day

Lifestyle:

• Reduce training volume -- overtraining is the most common cause in athletes
• Increase caloric intake if in severe deficit
• Improve sleep quality and duration (7-9h)
• If persistent, rule out viral infection (HIV, hepatitis) or autoimmune conditions

When high (lymphocytosis, >4.0 x10^9/L):

• Usually viral infection (EBV, CMV, influenza) -- transient and self-limiting
• Persistent lymphocytosis without infection warrants investigation

References:

• Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3), 266-281. DOI: 10.1056/NEJMra070553
• Prasad, A. S., Mantzoros, C. S., Beck, F. W. J., Hess, J. W., & Brewer, G. J. (1996). Zinc status and serum testosterone levels of healthy adults. Nutrition, 12(5), 344-348. DOI: 10.1016/S0899-9007(96)80058-X