Sun Exposure

The traditional dermatological position has been "the safest sun is no sun," and it stands up well for one outcome: melanoma and non-melanoma skin cancer scale roughly with cumulative UV dose. But long-running European cohorts point to strict avoidance being itself a measurable risk factor for all-cause, cardiovascular, and internal-cancer mortality. Read alongside the evidence on cumulative damage, the shape that best fits the data looks roughly J-like: low exposure is bad, very high exposure is bad, and a non-burning middle is best. A newer UK Biobank analysis — still an unreviewed preprint — finds the protective half of that curve but not the harmful half. The caveat is that the mortality evidence is entirely observational, and the most rigorous recent synthesis judged it mixed and insufficient to justify changing sun-protection guidance — so the framing below is a defensible reading of confounded data, not a settled fact.

What the evidence actually supports

Strong:

• Strict sun avoidance is associated with higher all-cause mortality in observational cohorts. The Melanoma in Southern Sweden (MISS) cohort followed 29,518 Swedish women for about 20 years; avoiders of sun exposure had roughly double the mortality of the highest-exposure group (HR 2.0, 95% CI 1.6–2.5), and those with moderate exposure a 40% higher rate (HR 1.4, 95% CI 1.1–1.7)^[1]. The range printed after each ratio is its 95% confidence interval — the span in which the true effect most plausibly sits; when that span crosses 1.0, the result is compatible with no effect at all. A follow-up analysis found the survival gap sat almost entirely in cardiovascular and other non-cancer deaths, and put the life-expectancy cost of avoidance at 0.6–2.1 years^[2]. The signal is biologically plausible but "avoidance" was self-reported and correlates with indoor lifestyle, lower activity, and comorbidity, so reverse causation and confounding are live concerns.
• Cumulative UV is the dominant driver of skin aging. Wrinkling, sun spots, the loss of elastic recoil dermatologists call solar elastosis, and the whole leathery weather-beaten look come from UV-driven matrix-metalloproteinase (MMP-1, -3, -9) activation degrading dermal collagen — not from chronological aging^[3][4].
• UVB-driven cutaneous vitamin D synthesis is the human default. Diet contributes a small fraction of typical vitamin D status; without sun or supplements, deficiency is the rule at temperate latitudes^[5].

Moderate:

• The dose-response looks roughly J-shaped, but the evidence is mixed. Strict avoidance and sunburn-level overexposure both appear worse than a non-burning middle. Markers of cumulative excess UV track with mortality: in the first National Health and Nutrition Examination Survey (NHANES I) follow-up of 8,472 white participants (1971–1992), severe sun damage visible on examination — sun spots, thread veins, coarsened texture — carried about 45% higher all-cause mortality (HR 1.45, 95% CI 1.22–1.72) and moderate damage 20% higher (HR 1.20, 95% CI 1.08–1.32)^[6]. Smoking was adjusted for and does not appear to drive that association, but visible damage remains a crude proxy for a lifetime UV dose nobody measured. The caveat that downgrades this from Strong: the leading 2025 systematic review — 55 studies, overwhelmingly ecological, not a single randomised trial among them — found the mortality evidence "too variable to provide a rationale for changes to sun protection guidance," with all included studies at some-to-very-high risk of bias^[7].
• Low vitamin D is largely a marker of low UV exposure, not the causal agent. Randomised and genetic evidence converge here: in the 25,871-participant VITAL trial, 2000 IU/day vitamin D3 left total invasive cancer essentially unchanged — a 4% difference well inside the range expected from chance (HR 0.96, 95% CI 0.88–1.06) — and did not reduce major cardiovascular events, leaving only a non-significant hint of fewer cancer deaths (about 17% fewer, HR 0.83, 95% CI 0.67–1.02)^[8]. Non-linear Mendelian randomization in the UK Biobank (n=307,601) found an L-shaped relationship — genetically low 25-hydroxyvitamin D, the standard blood measure of vitamin D status, raised mortality only in the deficient range, with no benefit from raising already-adequate levels^[9]. This is why supplement trials are largely null while sun-exposure cohorts show benefit: sunlight likely acts through non-vitamin-D pathways (nitric oxide, circadian, immune) — a pill replaces only one of the things sun deprivation removes.
• Steady exposure is melanoma-neutral; intermittent burning drives the risk. The foundational meta-analysis of 57 studies found intermittent sun exposure raised melanoma risk by about 60% (summary RR 1.61, 95% CI 1.31–1.99), while chronic outdoor and occupational exposure showed no association and if anything a slight protective tilt (RR 0.95, 95% CI 0.87–1.04). Sunburn history was a consistent risk factor throughout^[10].
• UVA-driven nitric-oxide release lowers blood pressure. Skin holds large stores of nitrogen-oxide species that UVA mobilises into bioactive nitric oxide; population blood pressure tracks with latitude and season, and an analysis of 342,457 dialysis patients across 2,178 US clinics found ambient UV linearly and inversely associated with pre-dialysis systolic blood pressure even after adjusting for temperature^[11][12]. The mechanism is genuine and the direction is consistent, but the magnitude is modest — on the order of a single millimetre of mercury across a seasonal swing, not the double-digit drop the raw regression coefficients look like at first glance. There is no individual UV dosimetry, and several authors hold relevant commercial ties (AOBiome, Relaxsol, Fresenius), so residual confounding remains live.
• UV exposure activates a real skin-brain axis. On UV exposure, keratinocytes locally synthesise corticotropin-releasing hormone, proopiomelanocortin, β-endorphin, and serotonin, and UVB induces β-endorphin in human skin. The opioid-like analgesia, naloxone-precipitated withdrawal, and conditioned aversion that define "UV addiction," however, come from mice; human relevance is inferred rather than demonstrated, and the human-focused syntheses are reviews, not outcome trials^[13][14].
• Bright morning sun anchors the circadian clock. Daylight intensity at the eyes, sensed by a dedicated class of light-detecting retinal cells, suppresses morning melatonin and sets the evening melatonin rise. This is the single highest-leverage cue for sleep timing — see Circadian rhythms.

Weak / preliminary:

• Non-classical UVB photoproducts (lumisterol, tachysterol) act through a different set of nuclear receptors from the classical vitamin D receptor — receptors that switch on antioxidant and anti-inflammatory gene programmes — and appear photoprotective in mechanistic and cell-culture work^[15]. Whether this matters clinically, i.e. whether sun-derived and oral vitamin D differ in long-term outcomes, is unsettled.
• Oral systemic photoprotectants — Polypodium leucotomos extract (PLE), astaxanthin, oral nicotinamide — show mechanistic and short-trial signal for reducing photoaging and actinic damage, but are not substitutes for sunscreen^[16].

Caution:

• Tanning beds, solarium use, and any history of sunburn elevate melanoma risk and should be treated as straightforwardly harmful. Pooled across 27 studies, ever having used a sunbed raised melanoma risk by about 20%, and starting before age 35 by about 87%^[17].
• Familial melanoma, a dense crop of irregular moles, very pale skin (types I–II on the Fitzpatrick skin-tone scale), or immunosuppression: there is no known "safe" intentional UV dose. Vitamin D status should be managed via oral supplementation, not sun^[18].

The mortality J-curve

Evidence: Moderate for the shape of the curve; Weak for any specific dose.

The evidence base on sun and mortality has shifted because the methodology improved. Early cohorts approximated lifetime UV exposure with proxies like birth year — which conflates UV with everything else that changed across the 20th century (indoor work, diet, smoking, screening intensity). The MISS cohort improved on that with structured sun-habit interviews. UK Biobank's Sun-BEEM index is a four-item exposure score (time outdoors, residential ambient UV, solarium use, sun-protection use); in 419,007 White-European participants it found a monotonic inverse dose-response for all-cause mortality — roughly 11% lower at medium exposure and 16% lower at high exposure compared with low (HR 0.89 and 0.84) — rather than a J-curve, with no clear dose-response for skin-cancer mortality but rising keratinocyte (non-melanoma) skin cancers. This is a medRxiv preprint that has not been peer-reviewed, so treat it as preliminary and not on the same footing as the published cohorts above^[19].

The picture across these analyses is consistent:

Skin-cancer risk and mortality risk move in opposite directions, and for a population without high melanoma genetic risk the observational balance tilts toward moderate exposure being net-positive. That said, the most rigorous synthesis to date is more cautious: across 55 studies (overwhelmingly ecological, no RCTs) the 2025 NIHR systematic review found roughly as many analyses pointing to benefit as to harm, judged every included study at some-to-very-high risk of bias, and concluded the evidence is too variable to warrant changing sun-protection guidance^[20]. The table reflects the direction of the better cohorts, not a settled consensus.

Why sun-derived vitamin D is not the same as a pill

Evidence: Strong for the kinetic difference; Weak for it mattering to any hard outcome.

Cutaneous vitamin D synthesis is a photochemical cascade: UVB (~290–315 nm) opens the B-ring of 7-dehydrocholesterol in epidermal keratinocyte and fibroblast membranes, generating previtamin D3, which rearranges itself over the following hours, driven by body heat alone, into cholecalciferol — vitamin D3 proper. The molecule is then released slowly to the bloodstream bound to vitamin-D-binding protein (DBP).

Three differences from oral D3 matter:

1. Sustained kinetics. The tracer study behind this claim irradiated seven volunteers and found that skin-made D3 travels in plasma almost entirely on DBP, giving slower delivery to the liver and a more sustained rise in circulating 25-hydroxyvitamin D; orally dosed vitamin D instead partitions into chylomicrons and lipoproteins and clears within roughly a day^[21]. The direction is well established. The widely repeated "2–3× longer half-life" figure is not — no head-to-head study has measured it, and the oral comparator in that experiment was vitamin D2 rather than D3.
2. No toxicity ceiling. Excess UVB photodegrades surplus previtamin D3 into lumisterol and tachysterol — sun cannot cause hypervitaminosis D. Oral D3, by contrast, can.
3. Local epidermal supply. Keratinocytes are poorly vascularised and don't reliably import DBP-bound systemic D from the bloodstream; they rely on their own UV-driven synthesis to drive antimicrobial-peptide production, differentiation, and DNA-repair signalling. Oral supplementation does not fully reach this compartment^[22].

Lumisterol and tachysterol, long dismissed as inert byproducts, are increasingly recognised as signalling molecules in their own right, binding a separate family of nuclear receptors that drive antioxidant and anti-inflammatory responses in skin^[23]. Whether this translates to differences in clinical outcomes between sun-derived and supplemented vitamin D is not yet established.

Practical implication. Maintain a steady serum 25-hydroxyvitamin D across the year. Beyond roughly 40° of latitude, north or south, sunlight is too weak to maintain vitamin D status in at least some winter months for everyone regardless of skin type — and further poleward the dead zone widens to roughly October through March — so oral vitamin D3 across the winter is the standard fix; see Vitamin D. Do not try to "bank" D in summer by deliberate overexposure: the photodegradation fail-safe means extra burning yields extra skin damage, not extra D^[24].

Cardiovascular and metabolic effects independent of vitamin D

Evidence: Strong for the mechanism; Moderate for a real but small blood-pressure effect.

UVA is the longer-wavelength, less DNA-damaging part of the spectrum, and it does something distinct: it photolyses cutaneous nitrogen-oxide stores into bioactive nitric oxide, which diffuses systemically and triggers arterial vasodilation. This is the most plausible mechanism behind the latitude and seasonal blood-pressure gradients seen across many populations: blood pressure peaks in winter and falls in summer, and the gradient survives adjustment for temperature^[25].

The effect is consistent enough to be visible in a 342,457-patient haemodialysis cohort with routine clinic blood-pressure recordings, where incident UV was inversely and linearly associated with pre-dialysis systolic pressure after adjustment for ambient temperature, age, sex, and body-mass index^[26]. Worth keeping the scale honest, because the published coefficients are easy to misread: they are expressed per 100 W/m² of incident UVB, while actual UVB at these clinics averaged about 15 W/m² and swings by only a few W/m² between winter and summer. Translated back to that real-world range, and after removing the larger temperature contribution, the attributable movement is on the order of 1 mmHg. A genuine population-level signal, not a treatment.

UV exposure also tracks with lower LDL-cholesterol, lower levels of the standard blood inflammation markers C-reactive protein and interleukin-6, and — in animal models — suppression of high-fat-diet–induced obesity that oral vitamin D does not reproduce^[27]. The implication is that low vitamin D in obese, hypertensive populations is partly a biomarker of UV deprivation rather than the upstream cause of their metabolic disease — and giving them a pill replaces only one of the things they're missing.

Mood, sleep, and the skin-brain axis

Evidence: Strong for the local hormone cascade; Weak for the addiction and mood claims in humans.

UV-exposed keratinocytes locally synthesise corticotropin-releasing hormone → proopiomelanocortin → β-endorphin and the two hormones that drive protective tanning; the skin runs its own miniature version of the brain's central stress axis. The β-endorphin reaches the systemic circulation and binds opioid receptors centrally — which is the proposed reason frequent sun exposure produces opioid-like analgesia and mood elevation, and why naloxone reliably triggers withdrawal in UV-habituated mice^[28][29]. The withdrawal and reward findings are from mice; the human end of this is inference.

The skin also generates serotonin from tryptophan independently of the central serotonin system. Cutaneous serotonin synthesis falls in winter, contributing to the signature of depression with a seasonal pattern, formerly called seasonal affective disorder^[30].

For sleep specifically: bright morning sunlight at the eyes is the strongest single time cue the body clock has. A dedicated nerve pathway carries the signal from the retina to the clock nucleus in the hypothalamus, which then sets the evening melatonin rise that allows sleep onset 14–16 hours later. The dose that matters is daytime brightness (10,000+ lux outdoors vs. 100–500 lux indoors), not UV per se — see Circadian rhythms.

What UV actually does to skin

Evidence: Strong — the mechanisms here are settled cell and molecular biology.

The visible signs of "old skin" — coarse wrinkling, leathery texture, sagging, sun spots, and the fine broken surface veins called telangiectasias — are mostly photoaging, not chronological aging. Compare sun-protected skin (e.g., the underside of an upper arm) with sun-exposed skin (the back of the same hand) in any 70-year-old: the difference is the cumulative UV history.

Mechanism. UV photons drive an immediate burst of reactive oxygen species in the epidermis and upper dermis. Those free radicals switch on a stress-signalling cascade that ends at two transcription factors — the master switches that decide which genes a cell transcribes. Their combined output is to:

• Massively upregulate MMP-1, the collagenase that makes the first cut in intact fibrillar collagen — the dermis's main load-bearing protein.
• Upregulate MMP-3 (stromelysin-1) — breaks down proteoglycans and fibronectin, and activates other latent MMPs.
• Upregulate MMP-9 (gelatinase B) — finishes off the fragmented collagen pieces.
• Down-regulate fibroblast procollagen synthesis at the same time, producing a structural deficit^[31].

UV also covalently modifies the collagen that survives, permanently oxidising specific amino-acid sites along the fibre in a way that disrupts how fibroblasts grip and contract the matrix^[32]. The matrix doesn't just thin; it stops working.

UVA penetrates deeply into the dermis and is the dominant driver of these changes. UVB penetrates less but causes most of the direct DNA damage — welding adjacent bases together into lesions the cell must cut out and rebuild — and is the dominant driver of skin cancer.

UV is also immunosuppressive. UVB-induced DNA damage triggers systemic, antigen-specific T-cell-mediated immunosuppression. The clinical signature is stark: solid-organ transplant recipients, who are pharmacologically immunosuppressed, develop cutaneous squamous-cell carcinoma at more than 65 times the background rate, with a smaller but real excess of basal-cell carcinoma^[33] — direct evidence that immune surveillance normally restrains UV-driven skin cancer. This is a distinct hazard from photoaging and from the direct mutagenesis above, and it is part of why a healthy immune system tolerates incidental sun that an immunosuppressed one cannot.

Repair runs on a clock. Nucleotide excision repair — the system that excises UV-induced DNA lesions — is itself circadian, with peak capacity at specific phases of the 24-hour cycle. UV exposure at hours of low repair activity (deep evening, night — e.g., tanning beds) measurably amplifies the per-photon mutagenic load^[34]. Solar UV during normal daytime hours hits the body when DNA repair is most active.

Skin type changes everything

Evidence: Strong — skin pigmentation is the single largest modifier of every trade-off on this page.

The Fitzpatrick scale tracks the eumelanin / pheomelanin balance. Lighter skin (Types I–III) is heavier in pheomelanin, which is a pro-oxidant under UV and amplifies free-radical damage. Darker skin (Types IV–VI) is heavier in eumelanin, a broad-spectrum filter and antioxidant.

Two practical numbers:

• Innate sun protection factor (SPF). Type I/II skin has an intrinsic SPF of about 3.3. Type V/VI skin has roughly 13.4. Eumelanin functions as built-in sunscreen^[35].
• Vitamin D synthesis time. Deeply pigmented skin needs several times the UVB exposure of pale skin to make the same amount of vitamin D. The best modelling estimates put the penalty at roughly three- to fivefold: the exposure-time model scales type V by about 2.5× and type VI by about 4×, and its worked equatorial example runs from about 3 minutes at noon for the palest skin to about 15 minutes for the darkest. Blanket sun-avoidance guidelines apply that penalty without compensating with stronger oral repletion advice — which is part of why severe vitamin D deficiency is endemic in dark-skinned populations at temperate latitudes^[36].

The 2024 revised Australian position statement formalises this with three risk groups^[37]:

1. Very high skin-cancer risk — Fitzpatrick I/II, immunosuppression, melanoma history, a dense crop of atypical moles. Year-round photoprotection; manage vitamin D with supplements.
2. High vitamin-D-deficiency risk, low skin-cancer risk — Fitzpatrick V/VI. Routine daily sunscreen during ordinary outdoor activity is discouraged; deliberate brief unprotected exposure to maintain vitamin D status is appropriate.
3. Intermediate — most of the population. Sub-erythemal exposure — short of the dose that reddens the skin — during incidental outdoor activity for systemic benefit; sunscreen for longer outdoor stretches and high UV index.

Practical guidance

Evidence: Moderate — the direction is well supported; the specific minute counts are modelled population averages, not measured doses.

Aim for micro-doses, not "tans"

The conversion of 7-dehydrocholesterol to previtamin D3 saturates quickly. Past that plateau, additional UV adds skin damage without adding vitamin D. The biologically efficient form is brief exposures of a lot of skin, repeated, not long exposures of small areas^[38].

A reasonable rule of thumb, for an intermediate skin type at midday with arms and legs uncovered:

These are population approximations from exposure modelling, not titratable prescriptions: real dose varies widely with how much skin is uncovered, age (the 7-dehydrocholesterol supply in skin declines over the years), and skin type, and the modellers' own conclusion is that precise self-titration is impractical. Spread exposure across the week; do not "stack" it. Time between sessions is what lets DNA repair clear UV-induced lesions before they accumulate.

Protect when exposure exceeds the synthesis dose

Once you're past the brief window that buys vitamin D and the nitric-oxide release — long beach days, alpine hiking, sustained outdoor work — the calculation flips and the goal is photoprotection.

• Broad-spectrum sunscreen (UVA + UVB). SPF 30–50 is sufficient for most skin types; SPF 50+ for Fitzpatrick I/II or with melanoma history. Trials of everyday sunscreen at around SPF 16 found no effect on vitamin D status, but the 2025 Sun-D randomised trial — the first to test high-SPF product — found that daily SPF 50+ use modestly lowered 25-hydroxyvitamin D — about 5 nmol/L lower than the control group over a year — and left more people below the deficiency threshold (45.7% vs 36.9%), so regular high-SPF users may need supplementation^[39].
• Hat, long sleeves, UV-blocking sunglasses. UV-driven cataracts, macular degeneration, and pterygium are real and largely preventable.
• Avoid sunburn. This is the single most useful bright line. Burning is what tracks with melanoma risk; exposure that stops short of reddening the skin largely does not.
• No tanning beds, ever. Their UV profile is not the daytime spectrum, exposure lands at hours when DNA repair capacity is lowest, and the risk-benefit balance is straightforwardly negative.

Oral systemic photoprotection — useful but adjunctive

A small, mechanistically coherent literature supports oral Polypodium leucotomos extract (PLE), astaxanthin, and oral nicotinamide as adjunct photoprotectants. Nicotinamide supports the energy-intensive DNA-repair machinery, and PLE — tested in skin cells and donated tissue, in combination with rooibos extract and by authors including one from the company that markets it — preserves vitamin D receptor levels in skin under oxidative stress^[40]. The strongest datapoint by some distance is the ONTRAC trial in 386 patients with prior non-melanoma skin cancers, where 500 mg nicotinamide twice daily cut new non-melanoma skin cancers by 23% over a year (95% CI 4–38)^[41]. That is a modest effect in high-risk patients only and should not be generalised to healthy adults; these are useful additions for high-exposure days, not substitutes for sunscreen or for not burning.

Cautions and contraindications

• Personal or strong family history of melanoma, a dense crop of atypical moles, prior skin cancer, immunosuppression, photosensitising medications (some antibiotics, retinoids, the antiarrhythmic amiodarone, some anti-inflammatory painkillers): treat sun primarily as a hazard. Get a yearly dermatology check; manage vitamin D with supplements.
• Pregnancy: moderate, non-burning sun is fine and relevant for vitamin D status. Watch for melasma, the blotchy facial pigmentation that sun and pregnancy hormones together provoke, especially in mid-tone to deep skin.
• Eye health: the lens absorbs most UVB; chronic UVA exposure is the macular-degeneration and cataract risk. Real UV-blocking sunglasses are cheap and worth wearing on bright days.
• Children: their thinner outer skin layer and higher remaining lifetime dose make burn-prevention the dominant priority; play in the sun short of any reddening is fine and useful for vitamin D.

What's overrated

• "Sunscreen causes vitamin D deficiency." Overstated, but no longer dismissible: daily SPF 50+ use does modestly lower 25-hydroxyvitamin D — roughly 5 nmol/L in the Sun-D trial — so it is a small real effect rather than a wholesale cause. Most population deficiency is still from indoor lifestyles and high latitude, not from sunscreen; regular high-SPF users simply have one more reason to keep oral D3 topped up.
• Tanning as a longevity strategy. Tans are visible UV damage; they are not the source of the cardiovascular and mood benefits of sun, which appear well short of the dose that reddens skin, long before tanning.
• "You can store vitamin D in summer for winter." The half-life of 25(OH)D is several weeks; a high-latitude summer cannot cover a high-latitude winter. Use oral D3 across the dark months — see Vitamin D.
• Oral D as a full substitute for sun. It restores systemic 25-hydroxyvitamin D but doesn't reproduce UVA-driven nitric oxide, the skin-brain axis, daytime circadian entrainment, or the local epidermal vitamin D supply. Useful, necessary at temperate latitudes — but not a complete replacement. No trial has yet pitted sun against equivalent oral D3 on a hard endpoint. The Australian SEDS study was designed to do exactly that, randomising sun-exposure advice against vitamin D supplementation with immune and cardiometabolic outcomes, but it has published a protocol and no results in the decade since^[42]. The question remains genuinely open, and nothing currently running looks likely to close it.

Further reading

• Hoel D, Berwick M, de Gruijl FR, Holick MF. The risks and benefits of sun exposure 2016. Dermato-Endocrinology 2016.^[43]
• Lindqvist PG et al. Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort. J Intern Med 2014;276:77–86.^[44]
• Lindqvist PG et al. Avoidance of sun exposure as a risk factor for major causes of death: a competing risk analysis of the MISS cohort. J Intern Med 2016;280:375–87.^[45]
• He W et al. Actinic skin damage and mortality — the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. PLoS One 2011;6:e19907.^[46]
• Gandini S et al. Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure. Eur J Cancer 2005.^[47]
• Manson JE et al. Vitamin D supplements and prevention of cancer and cardiovascular disease (VITAL). NEJM 2019.^[48]
• Sutherland JP, Zhou A, Hyppönen E. Vitamin D deficiency increases mortality risk in the UK Biobank: a nonlinear Mendelian randomization study. Ann Intern Med 2022.^[49]
• Haddad JG, Matsuoka LY, Hollis BW, Hu YZ, Wortsman J. Human plasma transport of vitamin D after its endogenous synthesis. J Clin Invest 1993;91:2552–5.^[50]
• Boniol M, Autier P, Boyle P, Gandini S. Cutaneous melanoma attributable to sunbed use: systematic review and meta-analysis. BMJ 2012;345:e4757.^[51]
• Chen AC et al. A phase 3 randomized trial of nicotinamide for skin-cancer chemoprevention (ONTRAC). NEJM 2015.^[52]
• Tran V et al. Effect of daily sunscreen application on vitamin D: findings from the open-label randomized controlled Sun-D Trial. Br J Dermatol 2025.^[53]
• Weller RB et al. Does incident solar ultraviolet radiation lower blood pressure? J Am Heart Assoc 2020.^[54]
• Slominski RM, Chen JY, Raman C, Slominski AT. Photo-neuro-immuno-endocrinology: how ultraviolet radiation regulates the body, brain, and immune system. PNAS 2024.^[55]
• Fell GL, Robinson KC, Mao J, Woolf CJ, Fisher DE. Skin β-endorphin mediates addiction to UV light. Cell 2014;157:1527–34.^[56]
• Reichrath J, Nürnberg B. Cutaneous vitamin D synthesis versus skin cancer development: the Janus faces of solar UV radiation. Dermato-Endocrinology 2009.^[57]
• Kift RC, Webb AR. Globally estimated UVB exposure times required to maintain sufficiency in vitamin D levels. Nutrients 2024.^[58]
• Neale RE et al. Balancing the risks and benefits of sun exposure: a revised position statement for Australian adults. Aust N Z J Public Health 2024.^[59]
• Gu J et al. Risk–benefit balance of habitual ultraviolet exposure for cardiovascular, cancer, and skin cancer mortality: UK Biobank cohort study. medRxiv 2026 — preprint, not peer-reviewed.^[60]
• Parkhouse T et al. The effects of sunlight exposure on mortality: a systematic review of epidemiological studies. NIHR Open Res 2025.^[61]