By Dr Chun Tang — MBChB (Manchester), MRCGP, MBA · Practising NHS & Private GP · Founder, Little Ox

NMN and Spring Immunity: Colds That Linger, Hay Fever Season and What Your Cells Actually Need Right Now

April is an interesting month clinically. In my surgery I see two seemingly contradictory patient groups simultaneously: people who have had a cold or chest infection that simply will not clear, dragging on for three, four, five weeks — and people whose hay fever has arrived early and aggressively, leaving them miserable on sunny days that should feel like a relief after winter.

Both groups are dealing with immune system problems. One is a failure of immune resolution — the infection has cleared but the inflammatory response hasn't fully switched off. The other is an immune overreaction — a misdirected response to harmless pollen that causes real suffering. And both have a meaningful connection to NAD+ that is worth understanding as we move into spring.

Why Your Immune System Is Under Particular Pressure Right Now

The end of winter is not a clean transition for your immune system. The UK cold and flu season runs from roughly October through March — five months of repeated viral exposures, each of which triggers an immune response, each of which consumes NAD+ through PARP enzyme activation. Every time your immune cells identify and fight an infection, they generate oxidative stress and DNA damage as a byproduct of the inflammatory response. PARP enzymes — which repair that DNA damage — are NAD+-hungry. A significant viral illness can substantially deplete cellular NAD+ levels.

For people over 40, whose baseline NAD+ is already declining at 1–2% per year, the cumulative NAD+ consumption across a winter of repeated immune challenges leaves them entering spring with depleted cellular metabolism reserves. This is one plausible explanation for the lingering fatigue and immune sluggishness that many people notice in March and April — not a new illness, but a system that hasn't fully recovered from the last several.

At the same time, pollen season is arriving. In the UK, tree pollen typically begins in March and peaks through April and May, with grass pollen following from May through July. For the 13 million UK adults with hay fever, this means months of histamine-mediated symptoms: sneezing, congestion, itching eyes, and the inflammatory fatigue that comes with a chronically activated immune system.

How NAD+ Is Involved in Both

For infections and lingering immune activation: NAD+ is required for every immune cell in your body to function. T cells, B cells, natural killer cells, macrophages — all depend on NAD+ for energy production, proliferation, signalling and the DNA repair that accompanies an immune response. Research published in Trends in Immunology confirmed that viral infections induce measurable NAD+ depletion through PARP activation, and that boosting NAD+ via precursors may help maintain immune capacity during and after infection.

Critically, NAD+ also supports the resolution of inflammation — the process by which the immune system stands down once a threat has cleared. Regulatory T cells (Tregs), which suppress excessive immune activation and restore immune homeostasis after an infection, are particularly dependent on adequate NAD+ for their function. When NAD+ is depleted, the resolution process slows. This is one cellular mechanism behind infections that "won't quite clear" — the immune system has enough energy to fight, but not enough to properly resolve.

For hay fever and seasonal allergies: The most directly relevant mechanism involves mast cells — the immune cells responsible for releasing histamine when they encounter allergens like pollen. Standard antihistamines work by blocking histamine receptors after histamine has already been released. The NAD+ mechanism appears to work upstream: laboratory studies found that NAD+-boosting molecules can inhibit mast cell degranulation — the release of histamine — through multiple cellular signalling pathways. A separate study confirmed that NAD+ precursors including NMN significantly suppressed allergic responses in human-derived mast cells.

The practical implication: antihistamines manage acute hay fever symptoms. NAD+ support may, over time, influence the underlying immune balance that determines how aggressively those symptoms develop. These are complementary approaches — one fast-acting and symptomatic, one slower and cellular.

The Gut Microbiome Connection — Often Overlooked at This Time of Year

Spring is also the time when many people's gut health has been compromised by winter — less dietary variety, more processed food, potentially a course of antibiotics during a winter illness. The gut microbiome has a direct relationship with immune regulation: roughly 70% of the immune system is located in or around the gut, and gut bacterial diversity directly influences T regulatory cell populations and the systemic inflammatory tone that determines how aggressively the immune system responds to triggers like pollen.

For patients I see with both persistent infection and hay fever, I often suggest addressing the gut-immune axis alongside NAD+ support. Our Bio Cultures Complex — 75 billion CFU across 25 strains — is the complementary intervention that addresses the gut side of this equation. NMN addresses cellular metabolism for immune function; Bio Cultures addresses the gut environment that immune regulation depends on.

What to Do — A Practical Spring Protocol

One More Thing — Sleep

Almost every immune problem I see in spring has a sleep component. Hay fever disrupts sleep. Winter illness disrupts sleep. Disrupted sleep impairs immune function — it is one of the most well-established relationships in immunology. NAD+ regulates circadian clock genes that govern the sleep-wake cycle, and a 2024 randomised controlled trial confirmed NMN supplementation improved recovery and overnight routine in older adults after 12 weeks. Better overnight recovery means a better-functioning immune system the following day. This is a compounding effect that works in both directions — better cellular metabolism supports better overnight recovery; better overnight recovery supports better immune function. Getting one right helps both.

Shop NMN Plus — from £9.99 → Shop Bio Cultures Complex — £9.99 → Shop Magnesium Glycinate — £9.99 →

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This article is for informational purposes only and does not constitute medical advice. NMN is a food supplement, not a medicine. If you have persistent symptoms, severe allergic reactions or recurrent infections, consult your GP. Do not stop or alter prescribed medication without medical advice.