Your Menstrual Cycle and Immune Response: Training Smarter Through Hormonal Shifts

Part 2 of a series on immune system health for active people. Here's Part 1.

Your ability to fight off a cold, respond to vaccination, or recover from training stress doesn't stay constant through your cycle. Estrogen and progesterone don't just regulate reproduction — they actively rewrite which immune cells dominate your system and how aggressively they respond. The immune response is very much nuanced and research in this area is still emerging. But I want you to take note of how to best support your immune system and what factors to take into account each day of the month.

The Two Immune Responses: TH1 and TH2

Your immune system has two main strategic pathways for fighting infection. Think of them as specializations:

TH1 (Cell-Mediated Immunity):

Your bacterial and intracellular viral fighters. TH1 cells are the aggressive pathogen-hunting response — direct cell-to-cell combat against invading pathogens inside your cells.

TH2 (Humoral Immunity):

Your antibody-producing response. TH2 cells coordinate the production of antibodies that circulate in your blood tagging invaders for destruction.

You need both. But which one dominates shifts based on the predominant hormones — and this directly impacts how well you fight infection at different cycle phases.

Follicular Phase: The TH1 Window

During the follicular phase (roughly days 1–14, depending on cycle length), rising estrogen upregulates TH1 response. This is your bacterial-fighting, intracellular-pathogen-hunting phase.

  • Your immune system is biased toward direct pathogen elimination

  • You mount a faster, more aggressive response to viral and bacterial invaders

For athletes: If you're exposed to a virus during your follicular phase, your immune system is better positioned to clear it quickly. This is also why follicular phase is when you can tolerate higher training load without immune suppression — your immune cells are activated and ready.

Luteal Phase: The TH2 Shift

During the luteal phase (roughly days 15–28, specifically this is a few days after ovulation until the next period), progesterone rises and suppresses TH1 while promoting TH2 response. This shift trades direct pathogen hunting for systemic antibody production. Why does this happen? The current hypothesis is that this is to protect a developing embryo.

  • Your immune system becomes less aggressive at cellular-level pathogen killing

  • You're more dependent on circulating antibodies for defense

  • This phase naturally promotes a more tolerant, less inflammatory immune posture — useful for pregnancy maintenance, but less useful for acute infection fighting

  • Symptoms of existing illnesses (especially respiratory ones) often worsen during luteal phase because you lack the TH1 firepower to clear pathogens efficiently

This TH2 dominance also explains something athletes notice: asthma and respiratory symptoms often worsen in the luteal phase, particularly in the 5 days before menstruation. Research shows measurable increases in airway reactivity and asthma exacerbations during the late luteal phase (1).

Training Strategy Around Immune Phase

Once you know how your immune response shifts, you can be hormone-informed and know how to focus your immune support.

Follicular phase - For many cycling people, this is the window for harder training blocks, higher training volume, and greater tolerance for intense sessions. Your immune system is primed and less susceptible to exercise-induced immune suppression. Exposure to viruses is more likely to resolve quickly.

Luteal phase -  Lean toward high quality sessions. Consider lower-intensity, higher-frequency training. Higher-intensity training during luteal phase compounds immune suppression (training itself downregulates TH1 temporarily). Prioritize recovery. Track any signs of respiratory infection — you're more vulnerable to symptoms worsening during this phase. Take immediate action to support the immune system if you’re exposed to a pathogen.

Late luteal (PMS window) -  If you're planning exposure to sick people, travel, or competition, acknowledge that your immune defense is at its lowest. Extra sleep, excellent nutrition, and avoiding unnecessary high-intensity training during this window matters. If you have some high-intensity scheduled (like a competition!) you can still go all-out. But you have to really dial in the recovery.

For Athletes – RED-S (relative energy deficiency in sport) has the global effect of reducing the immune response (2).

Clinically, I see this often when my athletes (even those who don’t describe themselves as athletes) are frequently batting colds and flus.

The Practical Edge: Cycle-Informed Training

You can't change your hormones. But you can change your recovery behaviours and immune-support efforts. If you get sick during luteal phase, expect longer symptom duration — don't rush back to intensity.

Connection to Your Larger Training System

This cycle-immune interaction is one piece of the larger hormone-informed performance puzzle. If you're already tracking how your cycle affects motivation and dopamine (see The Hormone-Dopamine Connection: Training With Your Cycle for Peak Drive), the immune pattern is the next logical layer. They're working in parallel — same hormonal shifts, different physiological systems.

PART 3 - Next in this series: Returning to Intense Training After Viral Infection: The Recovery Timeline That Actually Works

References

1 - 1- Farha S, Asosingh K, Laskowski D, Hammel J, Dweik RA, Wiedemann HP, Erzurum SC. Effects of the menstrual cycle on lung function variables in women with asthma. Am J Respir Crit Care Med. 2009 Aug 15;180(4):304-10. doi: 10.1164/rccm.200904-0497OC. Epub 2009 Jun 11. PMID: 19520904; PMCID: PMC2731807.

2 - Cabre HE, Moore SR, Smith-Ryan AE, Hackney AC. Relative Energy Deficiency in Sport (RED-S): Scientific, Clinical, and Practical Implications for the Female Athlete. Dtsch Z Sportmed. 2022;73(7):225-234. doi: 10.5960/dzsm.2022.546. Epub 2022 Nov 1. PMID: 36479178; PMCID: PMC9724109.