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

Get Outside — But Protect Your Cells: NMN, Sunlight and What Huberman Gets Right

There is a tension at the heart of the modern conversation about sunlight. On one hand, Andrew Huberman — Stanford neuroscientist and one of the most followed science communicators alive — tells us that morning sunlight is perhaps the single most important thing we can do for our health. On the other hand, decades of dermatological advice have drilled into us that UV exposure damages skin, ages it prematurely and raises cancer risk.

Both things are true. And understanding how they can be reconciled — rather than one cancelling the other out — is where NMN becomes genuinely relevant.

Huberman's Case for Sunlight — and Why He's Right

Andrew Huberman's sunlight protocol is not wellness culture speculation. It is grounded in well-established circadian biology, and as a clinician who understands the underlying mechanisms, I think it deserves to be taken seriously.

Huberman calls morning sunlight viewing one of the top five actions that support mental health, physical health and performance — alongside sleep, movement, nutrition and relationships. His exact words on the subject: "Getting sunlight in your eyes first thing in the morning is absolutely vital to mental and physical health. It is perhaps the most important thing that any and all of us can and should do in order to promote metabolic well-being, promote the positive functioning of your hormone system, get your mental health steering in the right direction."

The mechanism is this. Specialised cells in the lower retina — intrinsically photosensitive retinal ganglion cells containing melanopsin — detect the specific wavelengths and intensity of morning sunlight and signal the suprachiasmatic nucleus (SCN) in the hypothalamus. This triggers a cortisol pulse that anchors the circadian clock, sets a 16-hour timer for melatonin release later that evening, and activates the dopamine and norepinephrine systems that drive daytime focus and motivation.

Huberman's protocol: outside within the first hour of waking, facing toward (not directly at) the sun, for 5–10 minutes on sunny days and 15–20 minutes on overcast days. No sunglasses — they filter the wavelengths that trigger the mechanism. Through glass doesn't work — windows filter too much. He also highlights afternoon skin exposure: 20–30 minutes of sunlight on arms and legs in the afternoon has been shown to increase testosterone, oestrogen, mood and reproductive-health research in both men and women.

The clinical evidence supports all of this. Morning light exposure anchors cortisol rhythm, improves recovery and overnight routine, regulates appetite hormones, supports immune function, elevates serotonin and reduces the risk of seasonal affective disorder. These are not marginal effects.

The Problem Huberman Doesn't Fully Solve — What UV Actually Does to Your Cells

Here is where the cellular biology gets interesting, and where NMN enters the picture.

When UV radiation from sunlight hits your skin cells, it causes DNA damage — specifically the formation of cyclobutane pyrimidine dimers (CPDs) and oxidative DNA lesions. Your body has repair systems for this damage, but those repair systems are energy-dependent. They require ATP and, critically, they require NAD+.

The repair enzyme primarily responsible — PARP (poly ADP-ribose polymerase) — consumes large quantities of NAD+ when it activates in response to UV-induced DNA damage. Research published in the Journal of Photochemistry and Photobiology demonstrated precisely this mechanism: UV radiation triggers PARP activation, PARP consumes NAD+, and when NAD+ runs out, skin cells can no longer proliferate or repair themselves properly. The result, over time, is photoageing, impaired skin renewal and increased vulnerability to UV-induced cellular dysfunction.

This is not a theoretical risk. Every time you spend time in the sun — even following Huberman's healthy morning protocol — you are triggering this NAD+-depleting process in your skin cells. For people over 40, whose baseline NAD+ levels are already declining by 1–2% per year, repeated UV exposure compounds the depletion.

NMN Restores What UV Takes Away

The same research group that established the UV/PARP/NAD+ depletion mechanism also demonstrated the solution: supplementing with NMN restores the skin cells' ability to recover from UV damage. When NAD+ precursors were provided to UV-damaged cells, they were able to override the PARP-induced depletion, restore energy production and resume normal cell proliferation and repair.

A 2025 study comparing NAD+ precursors in human skin fibroblasts exposed to UV damage found that NMN outperformed NR, nicotinamide and NAD+ itself. NMN reduced cellular ageing by 30%, restored the expression of collagen-producing genes COL1A1 and COL3A1 that UV exposure suppresses, and activated the sirtuin repair proteins SIRT5 and SIRT6. Crucially, the protective effect on collagen persisted for more than 10 days after treatment — suggesting a lasting restoration of skin's self-repair capacity rather than a transient effect.

The collagen finding is particularly significant. UV-induced collagen breakdown is the primary mechanism of photoageing — the fine lines, loss of elasticity and skin thinning that sun exposure accelerates over time. NMN appears to work by restoring the cellular metabolism infrastructure that collagen synthesis and repair depends on.

Earlier clinical-grade evidence also comes from the family of NAD+ precursors: nicotinamide (vitamin B3, a related molecule) has been shown in Phase 2 randomised controlled trials to significantly reduce premalignant actinic keratoses — the sun-damaged lesions that precede non-melanoma skin cancer — and to enhance DNA repair in human keratinocytes and melanocytes following UV exposure. The mechanism runs through the same NAD+ pathway that NMN addresses more directly.

The Right Way to Think About This

NMN is not sunscreen. It does not block UV radiation. It does not replace SPF on your face in summer. These are fundamentally different mechanisms and I want to be clear about that distinction.

What NMN does is support the cellular repair infrastructure that deals with UV damage after it occurs. Think of it this way:

• Sunscreen — reduces the amount of UV that reaches your skin cells
• NMN — supports your cells' ability to repair the UV damage that gets through

These are complementary, not competing. The person who follows Huberman's protocol — getting outside in the morning and afternoon sun regularly — is doing something genuinely good for their circadian health, hormone balance and mood. They are also accumulating UV exposure that triggers PARP-mediated NAD+ depletion in their skin cells. NMN addresses the second consequence without undermining the first benefit.

The Circadian Overlap — One More Reason NMN and Sunlight Work Together

There is a deeper connection between NAD+ and Huberman's sunlight work that is worth understanding. The circadian clock genes that morning sunlight activates — CLOCK, BMAL1 and the sirtuin SIRT1 that regulates them — are the same genes that NAD+ supports. SIRT1, which is activated by NAD+, rhythmically deacetylates BMAL1 as part of the 24-hour oscillation of the circadian clock. Lower NAD+ means reduced SIRT1 activity, which means a less precise, less responsive circadian clock.

In other words: morning sunlight sets the circadian clock via the eyes. NAD+ (and therefore NMN) maintains the molecular clock machinery that makes that setting stick throughout the day. They are working on the same system from different angles. Getting sunlight without adequate NAD+ is like setting the alarm correctly but running on a battery that's running low.

The Practical Protocol

Why This Matters More After 40

The intersection of UV exposure and NAD+ decline is particularly significant for people in their 40s and beyond — exactly the age at which people are most likely to be following Huberman's protocols and most likely to have noticed their skin's recovery from sun exposure slowing down.

Baseline NAD+ levels at 50 are roughly half what they were at 25. The PARP-mediated DNA repair system in skin cells is therefore starting from a more depleted position every time you go outside. The cumulative photoageing that most people notice accelerating through their 40s is partly a consequence of this. NMN doesn't reverse existing sun damage — but it supports the cellular infrastructure to manage new UV exposure more efficiently.

At £9.99 a month for NMN Plus, it is a low-cost addition to what is already — if you follow Huberman's advice — a commitment to spending more time in natural light.

Shop NMN Plus — from £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. The protocols described are based on publicly available research and the published views of cited individuals; this does not imply endorsement of Little Ox. Always use appropriate sun protection for prolonged sun exposure and consult your GP or dermatologist regarding any concerns about your skin or sun damage.