Vitamin D and Skin Health

Evidence Snapshot

• 41.6% of US adults have vitamin D deficiency (defined as serum levels ≤20 ng/mL), with even higher rates among Black Americans (82.1%) and Hispanic Americans (69.2%)—a public health issue with significant skin health implications.

• Sunscreen does NOT meaningfully reduce vitamin D levels in real-world use: while laboratory studies show sunscreen reduces cutaneous vitamin D synthesis by 75-92%, actual circulating vitamin D levels decrease only 7-13%, suggesting the body compensates through diet and incidental sun exposure.

• The UV paradox is real: the same UVB wavelengths that cause vitamin D synthesis (290-320 nm) also cause DNA mutations leading to skin cancer—regular sunscreen use (SPF 15+) reduces melanoma risk by ~50% while dietary or supplemental vitamin D provides protection without UV damage.

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What Is Vitamin D and What Does It Do for Your Skin?

Vitamin D is a hormone your body produces naturally when sunlight hits your skin, and it's also found in certain foods and supplements. But vitamin D is far more than just a "sunshine vitamin"—it's a critical regulatory molecule that controls dozens of processes in your skin.

Within skin cells, vitamin D works through a receptor called the vitamin D receptor (VDR), which acts like a master switch. When vitamin D binds to VDR, it turns on genes that control how your skin cells grow, divide, and die. It also regulates your skin's outer barrier—the layer of dead cells and lipids that protect you from infection and water loss. Vitamin D stimulates the production of barrier proteins like loricrin and filaggrin, which are essential for maintaining that protective wall.

Beyond barrier function, vitamin D acts as an immunomodulator in your skin. It enhances the function of immune cells like dendritic cells and macrophages, boosting their ability to fight bacteria and other pathogens. At the same time, it tamps down excessive inflammation by promoting specific types of immune responses (Th2 cells) while dampening inflammatory ones (Th1 cells). This is why vitamin D deficiency has been linked to worse outcomes in inflammatory skin diseases like psoriasis, atopic dermatitis, and acne.

Vitamin D also protects against oxidative stress—the cellular damage caused by free radicals. It activates antioxidant defense systems in your skin cells, including pathways that produce protective enzymes like superoxide dismutase and glutathione peroxidase. This matters especially as you age, since oxidative stress accumulates over time and contributes to photoaging (sun-induced aging) and skin degradation.

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How Does Your Skin Actually Make Vitamin D?

Your skin makes vitamin D through a straightforward but sun-dependent process. When UVB radiation (specifically wavelengths between 290-320 nanometers) from sunlight penetrates your skin, it converts a cholesterol-like molecule called 7-dehydrocholesterol into previtamin D3. Heat from your body then converts this previtamin D3 into active vitamin D3.

This newly formed vitamin D3 then travels to your liver, where it's converted into 25-hydroxyvitamin D [25(OH)D]—the form doctors measure in blood tests to assess your vitamin D status. Finally, your kidneys convert this to the most active form, 1,25-dihydroxyvitamin D, which does the work we described above.

The problem is that vitamin D synthesis from sun exposure is highly variable and depends on several factors: your skin tone (darker skin requires 3-6 times more sun exposure), your age (older skin is less efficient), the time of day (midday sun produces more vitamin D than morning or evening sun), the season, your latitude, and even the amount of skin exposed.

The latitude factor matters especially if you live in the Midwest. At latitudes above 33 degrees North—which includes Kansas, Missouri, and most of the northern US—the sun's angle during winter months (roughly September through May) is so low that UVB rays don't penetrate the atmosphere effectively. Residents of Overland Park, Kansas (latitude ~39° N) can expect essentially zero vitamin D synthesis from sun exposure during these winter months, despite clear skies. This means that from fall through spring, dietary sources and supplements become the primary way to maintain adequate vitamin D levels in this region.

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The UV Paradox: You Need Sun for Vitamin D, But Sun Causes Skin Cancer

This is the central tension in vitamin D and skin health: the UVB wavelengths that make vitamin D are the same wavelengths that cause melanoma and non-melanoma skin cancers. Both vitamin D synthesis and skin cancer risk depend on the very same 290-320 nm wavelengths of ultraviolet radiation.

Here's what the evidence shows. Chronic sun exposure increases your risk of melanoma and squamous cell carcinoma (the two most common skin cancers) by damaging DNA in skin cells. UV radiation causes genetic mutations—primarily in the BRAF and KIT genes for melanoma—that can accumulate over decades and eventually trigger cancer. There's no "safe" threshold for cumulative UV exposure; each sunburn and each hour of sun exposure adds to your lifetime risk.

Yet at the same time, the sun is the most abundant and cheapest source of vitamin D. The problem: you cannot reliably get enough vitamin D from sun exposure in most climates without increasing your skin cancer risk.

The scientific consensus is clear: the benefits of sunscreen in preventing skin cancer far outweigh any theoretical benefit of trying to get vitamin D from the sun. Regular use of SPF 15 or higher broad-spectrum sunscreen reduces your risk of melanoma by approximately 50% and squamous cell carcinoma by approximately 40%. These are massive protective effects.

The solution is not to abandon sun protection but to get vitamin D from sources that don't carry cancer risk: food, supplements, and brief incidental sun exposure for general health without trying to achieve vitamin D synthesis specifically.

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Does Sunscreen Cause Vitamin D Deficiency? Debunking a Common Myth

One of the most persistent myths in health is that sunscreen prevents your skin from making vitamin D, leading people to avoid sun protection because they worry about becoming deficient. The evidence on this is nuanced and more complicated than a simple "true" or "false."

What laboratory studies show: Under controlled conditions, sunscreen does block UVB radiation and reduce cutaneous vitamin D synthesis significantly. Studies applying sunscreen in a laboratory setting show reductions in vitamin D production by 75-92%, depending on SPF level and application thickness.

What real-world studies show: The picture is more complex when people use sunscreen in everyday life. A recent systematic review and meta-analysis of 22 studies involving over 9,000 participants found that sunscreen use was associated with a reduction in serum 25(OH)D levels of approximately 2 ng/mL—a statistically significant but modest decrease. However, other large observational studies found little to no association between regular sunscreen use and vitamin D deficiency when researchers accounted for dietary intake and supplements.

The most recent evidence: A 2025 randomized controlled trial called the Sun-D Trial directly tested whether daily high-SPF sunscreen use causes vitamin D deficiency. Participants who regularly applied SPF 50+ sunscreen had a vitamin D deficiency rate of 45.7%, compared to 36.9% in a control group—a meaningful difference, though still lower than rates in the general population. Importantly, the deficiency was mild in most cases, and the researchers noted that dietary intake of vitamin D (milk, fortified cereals, supplements) easily compensated for reduced skin synthesis.

Why the disconnect between lab and real-world studies? Several factors explain why sunscreen doesn't cause widespread vitamin D deficiency despite reducing synthesis:

1. Most people don't apply sunscreen perfectly. Laboratory studies use thick, uniform applications. In real life, people apply less, miss spots, and reapply inconsistently.

2. Incidental sun exposure counts. Even if you wear sunscreen daily, you're getting some UVB exposure through gaps, during reapplication, and on your face and hands when you're not trying to protect skin.

3. Dietary intake provides a cushion. One serving of wild salmon provides 450-700 IU of vitamin D—about 75% of the daily recommended amount. Fortified milk, eggs, and supplements all contribute.

4. The body has storage capacity. Vitamin D is fat-soluble, so it accumulates in body tissues over time. A few months of good sun exposure in spring and summer can build reserves that partially sustain you through winter.

Bottom line on sunscreen and vitamin D: Sunscreen use can modestly reduce vitamin D synthesis, but it does not cause deficiency if you eat a reasonable diet (that includes foods like fish, eggs, or fortified dairy) or take a supplement. The vitamin D deficiency epidemic is driven by overall lifestyle factors—more indoor time, reduced dietary sources, less incidental sun exposure—not by sunscreen use. If you're concerned about vitamin D adequacy, the solution is straightforward: get your vitamin D from food and supplements, not from trying to compensate with reduced sun protection.

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Who Is Deficient in Vitamin D and Why?

Vitamin D deficiency is remarkably common in the United States. Approximately 41.6% of US adults have serum 25(OH)D levels of 20 ng/mL or lower—the threshold for deficiency. Another large segment of the population has levels between 20-29 ng/mL, which is considered insufficient. This means roughly 60% of American adults have either deficiency or insufficiency.

The problem is not evenly distributed. Certain populations bear a disproportionate burden:

• Black Americans: 82.1% have vitamin D deficiency
• Hispanic Americans: 69.2% have vitamin D deficiency
• Older adults: Aging skin produces vitamin D less efficiently
• People with obesity: Vitamin D is fat-soluble and gets sequestered in adipose tissue, reducing circulating levels
• People with limited sun exposure: Those living in northern climates, working indoors, or who cover their skin for cultural or medical reasons

Other risk factors for deficiency include low education level, hypertension, and not consuming milk or fortified foods daily.

Why is deficiency so common? Several converging factors:

1. Modern lifestyle: Most people spend 90% of their time indoors. Office work, school, and screen time limit incidental sun exposure.

2. Geographic and seasonal constraints: At latitudes above 33° North, winter sun cannot produce vitamin D. Overland Park, Kansas residents get essentially zero vitamin D synthesis from November through March.

3. Dietary inadequacy: Average vitamin D intake from food is only 4-5 mcg per day, far below the 10-20 mcg recommended daily intake. Most Americans would need to eat wild salmon or mackerel multiple times per week to meet vitamin D needs from diet alone.

4. Skin tone: Melanin in skin absorbs UVB radiation, so people with darker skin tones require 3-6 times more sun exposure to produce the same amount of vitamin D. This contributes to dramatically higher deficiency rates in Black Americans.

5. Sunscreen use for skin cancer prevention: While not the primary driver, consistent sunscreen use without dietary compensation does reduce synthesis.

Testing for vitamin D deficiency: If you're concerned about your vitamin D status, your doctor can order a simple blood test measuring 25-hydroxyvitamin D [25(OH)D]. This is the gold standard for assessing vitamin D adequacy. Guidelines define:

• Deficiency: < 20 ng/mL (50 nmol/L)
• Insufficiency: 20-29 ng/mL
• Sufficiency: 30-100 ng/mL
• Excess: > 100 ng/mL (rare from food and sun, but possible with supplements)

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Should I Get Vitamin D From the Sun or Supplements?

This is the central practical question, and the answer is unambiguous: get your vitamin D from supplements and food, not from intentional sun exposure.

Here's why: to synthesize enough vitamin D from sun exposure without supplements, most people would need 10-30 minutes of midday sun on exposed skin several times per week during summer months. In practice, most people either:

1. Don't get enough sun exposure (and end up deficient), or
2. Get enough sun exposure (and increase their skin cancer risk)

The research is clear that intentional sun seeking for vitamin D is not an appropriate public health strategy. The number of melanomas you would prevent by achieving optimal vitamin D levels through sun exposure is vastly outweighed by the melanomas and non-melanoma skin cancers you would develop from the same sun exposure.

Instead, use this strategy:

• In summer: Wear sunscreen daily. You'll still get adequate incidental sun exposure on your face, hands, and other exposed areas without actively seeking it. This is sufficient to build and maintain vitamin D stores.

• Year-round, especially in winter: Consume vitamin D-rich foods or take a supplement.

• In northern climates like Kansas: Supplements or fortified foods are essential during winter months when sun synthesis is impossible.

This approach eliminates the false choice between skin cancer risk and vitamin D adequacy. You get cancer protection and nutritional adequacy simultaneously.

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Vitamin D Sources: Sun, Food, and Supplements Compared

Source	Typical Dose	Pros	Cons	Evidence Quality
Sun Exposure (Midday, Summer)	200-400 IU per 10-15 min (varies by skin tone, latitude, season)	Free; natural; also provides other health benefits	Increases skin cancer risk; inconsistent and variable; impossible in winter at northern latitudes	Strong evidence of skin cancer risk; inconsistent vitamin D production
Fatty Fish (Wild Salmon, 3.5 oz)	400-700 IU (wild salmon); 100-200 IU (farmed salmon)	Nutrient-dense; provides omega-3 fatty acids and other benefits; sustainable whole food	Limited availability; cost; some species concerns; variable vitamin D content	Strong evidence of vitamin D content; nutritional benefit established
Egg Yolks (1 large egg)	37 IU (conventional); 100-150 IU (pasture-raised)	Accessible; affordable; whole food	Low dose; would need many eggs daily; not a sole source	Moderate evidence; variable by farming method
Fortified Milk (1 cup)	100 IU (varies by brand)	Widely available; affordable; established standard	May not be sufficient alone; lactose issues for some; not all milk is fortified equally	Strong evidence of fortification and absorption
Fortified Cereals (1 serving)	40-100 IU (varies widely)	Convenient; affordable	Highly variable between brands; often comes with added sugars	Moderate evidence; brand-dependent
Supplements (Oral, D2 or D3)	400-4,000 IU per dose (varies by formulation)	Reliable; consistent dosing; can correct deficiency quickly; affordable; works year-round	Requires adherence; some people concerned about synthetic; risk of excess with very high doses	Very strong evidence; extensively studied

Bottom line: For most people, the ideal strategy combines modest sun exposure in summer (protected with sunscreen after 15 minutes), some dietary sources (especially fatty fish 1-2 times per week), and a supplement during winter months or year-round if you live at northern latitudes or have other risk factors.

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What About Vitamin D and Melanoma Risk?

The relationship between vitamin D and melanoma is complex and sometimes contradictory. There are two competing sets of observations:

Observational evidence suggesting low vitamin D worsens melanoma outcomes:

Research has found that patients with metastatic melanoma who have vitamin D deficiency (≤20 ng/mL) have worse survival outcomes. In one study of 71 patients with stage IV metastatic melanoma, those with deficiency had a hazard ratio of 2.06—meaning roughly double the risk of death during follow-up compared to those with adequate vitamin D. Notably, patients who started deficient and remained deficient or improved minimally had even worse outcomes, with a hazard ratio of 4.68. Additionally, melanomas in vitamin D-deficient patients tend to be thicker and have higher-risk features like ulceration and higher mitotic index.

The prevalence of vitamin D deficiency is also higher in melanoma patients than in controls: 49.4% of melanoma patients versus only 19.2% of controls in one analysis.

Intervention evidence suggesting supplementation doesn't prevent or improve melanoma:

Despite the association between low vitamin D and worse melanoma outcomes, attempts to improve outcomes through supplementation have been unsuccessful. The ViDMe trial, a randomized controlled trial published in 2024, tested whether high-dose vitamin D supplementation (4,000 IU monthly) could improve outcomes in cutaneous melanoma patients. The study found that supplementation was safe and successfully increased 25(OH)D levels, but it did not improve relapse-free survival, melanoma-related death, or overall survival. This suggests that while low vitamin D is associated with worse outcomes, simply correcting the deficiency through supplementation may not improve melanoma prognosis.

What does this mean? The most likely explanation is that vitamin D deficiency is a marker of overall poor health, limited sun exposure (paradoxically protective for melanoma risk), or other unfavorable prognostic factors—rather than a direct cause of worse melanoma outcomes. While maintaining adequate vitamin D is important for general skin health and immune function, it should not be pursued through sun exposure in the hopes of reducing melanoma risk. The melanoma risk from increased UV exposure far exceeds any benefit from improved vitamin D status.

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How Much Vitamin D Do You Need? Guidelines and Recommendations

Different expert organizations have slightly different recommendations, but they're generally consistent:

National Academy of Medicine (formerly National Academies of Sciences, Engineering, and Medicine):

• 400 IU daily for children and adults up to age 70
• 600 IU daily for children and adults ages 1-70 years
• 800 IU daily for adults over 70 years
• Upper safe limit: 4,000 IU daily for adults

Endocrine Society Clinical Practice Guidelines:

• Higher recommendation: 1,500-2,000 IU daily for adults (to target levels of 30 ng/mL)
• This is higher than the NAS recommendation and is increasingly accepted by specialists

For deficiency correction: If you have documented vitamin D deficiency (< 20 ng/mL), your doctor may recommend higher doses—typically 2,000-4,000 IU daily or even higher doses to correct the deficit more rapidly, sometimes followed by a maintenance dose.

Special populations:

• Breastfed infants: 400 IU daily supplement
• Older adults with poor mobility: 800 IU daily is the minimum; many specialists recommend up to 2,000 IU
• People with darker skin tones: May benefit from higher supplementation given reduced skin synthesis
• People living at northern latitudes (like Kansas): Should consider year-round supplementation, especially October-April
• People with malabsorption disorders: May need higher doses

Important note on upper limits: The safe upper limit is 4,000 IU daily for adults. Doses above this can cause vitamin D toxicity, which is rare but serious, causing hypercalcemia (too much calcium in the blood). This is primarily a risk with supplements, not with sun exposure or food.

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Should You Take a Vitamin D Supplement?

A supplement makes sense if any of these apply to you:

• You live north of 33° latitude (which includes virtually all of Kansas, Missouri, Illinois, and the northern US) and experience winter months—you should supplement October through April at minimum, or year-round
• You have documented vitamin D deficiency (measured blood level < 20 ng/mL)
• You spend most of your time indoors for work or medical reasons
• You follow strict sun protection with sunscreen and protective clothing
• You have darker skin (increased melanin reduces vitamin D synthesis)
• You have limited access to vitamin D-rich foods (fatty fish, fortified dairy, eggs)
• You are over 70 years old (skin synthesis declines with age)
• You have a malabsorption disorder (celiac disease, Crohn's disease, cystic fibrosis, etc.)
• You take medications that interfere with vitamin D (some anticonvulsants, glucocorticoids)

How to choose a supplement:

Look for supplements labeled "vitamin D2" (ergocalciferol) or "vitamin D3" (cholecalciferol). Vitamin D3 is slightly more effective at raising blood levels, especially with smaller doses. Doses typically range from 400 to 5,000 IU per capsule or gummy. For most people, 1,000-2,000 IU daily is sufficient for maintenance; if you have deficiency, your doctor may recommend 2,000-4,000 IU daily until levels normalize, then switch to maintenance.

Cost is minimal—bottles of 100-200 tablets are typically $5-15 for several months' worth of supplementation.

Timing and absorption: Take vitamin D with a meal containing fat (olive oil, nuts, fish, avocado, etc.) for optimal absorption, since vitamin D is fat-soluble.

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Vitamin D and Other Skin Conditions

Beyond its general role in skin barrier function and immune regulation, vitamin D has been studied in several specific skin conditions:

Psoriasis: Observational studies show an inverse relationship between vitamin D levels and psoriasis severity. Patients with psoriasis have lower average vitamin D levels than controls, and some small trials suggest that vitamin D supplementation or topical vitamin D analogs (calcipotriene) can improve symptoms. However, large randomized trials demonstrating definitive benefit are lacking.

Atopic Dermatitis (Eczema): Multiple studies have found that vitamin D deficiency is more common in patients with atopic dermatitis, and disease severity correlates inversely with vitamin D levels. Vitamin D supports the production of antimicrobial peptides and maintains tight junction proteins essential for barrier function—both of which are impaired in atopic dermatitis. Small supplementation trials have shown promise, though larger trials are needed.

Acne Vulgaris: Some research suggests vitamin D deficiency is more common in acne patients, particularly those with severe acne. This may relate to vitamin D's role in regulating sebaceous gland function and its antibacterial properties against Propionibacterium acnes. However, evidence for supplementation is limited.

Hidradenitis Suppurativa: This chronic inflammatory condition of the apocrine glands is associated with vitamin D deficiency in some studies. Given the disease's inflammatory nature and vitamin D's immunomodulatory properties, supplementation is sometimes recommended, though robust evidence is limited.

General skin aging and photoaging: Vitamin D's antioxidant and anti-inflammatory properties suggest it may protect against photoaging (sun-induced aging). Its role in regulating tight junction proteins and promoting barrier integrity also suggests potential benefits for maintaining skin health with aging.

Bottom line: While vitamin D appears to play a role in multiple inflammatory skin conditions, supplementation is not yet definitively proven to improve outcomes in any of them beyond maintaining general health. Maintaining adequate vitamin D levels is reasonable for overall skin health, but it should not be viewed as a substitute for proven treatments like topical corticosteroids for eczema or standard acne therapies.

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FAQ: Your Vitamin D and Skin Questions Answered

Q1: Can I get all the vitamin D I need from food?

It's possible but challenging. One serving of wild salmon provides 450-700 IU, and three servings per week could meet your needs if combined with other dietary sources like fortified milk, eggs, and mushrooms. However, farmed salmon has only about 100-200 IU per serving. Most Americans don't eat enough vitamin D-rich foods, which is why supplements are often necessary, especially in winter at northern latitudes.

Q2: Is vitamin D3 better than vitamin D2?

Vitamin D3 (cholecalciferol) is slightly more effective at raising blood levels, particularly with smaller doses, and is the form your skin naturally produces. Vitamin D2 (ergocalciferol) comes from plant sources and is less expensive but slightly less potent. For most people, either is acceptable, but D3 is preferred if available.

Q3: Can you get too much vitamin D?

Yes, but it's rare with reasonable supplementation. Toxicity typically occurs with doses above 10,000 IU daily sustained over weeks to months, causing high blood calcium levels (hypercalcemia). The safe upper limit is 4,000 IU daily. You cannot get too much vitamin D from sun exposure or food—toxicity is almost exclusively a supplement issue with very high doses.

Q4: Does vitamin D help with rosacea?

There is limited research on vitamin D specifically for rosacea. However, given vitamin D's anti-inflammatory properties and its role in immune regulation, maintaining adequate levels is reasonable for overall skin health. Rosacea treatment is best discussed with your dermatologist, as proven treatments include topical medications, oral antibiotics, and laser therapy.

Q5: If I'm taking vitamin D, do I still need sunscreen?

Absolutely yes. Sunscreen protects against melanoma and non-melanoma skin cancers through its ability to block UV radiation. Vitamin D supplementation does not provide this protection. Sunscreen and vitamin D supplementation are complementary strategies, not competing ones: use sunscreen for cancer prevention, and supplement with vitamin D for health.

Q6: Should I test my vitamin D level?

If you have risk factors for deficiency—living at northern latitude, limited sun exposure, dark skin tone, documented inflammatory skin disease, or age over 70—testing is reasonable. A simple blood test measuring 25-hydroxyvitamin D is the gold standard. If you're deficient, supplementation is straightforward and effective. If you're sufficient, you can feel confident in your sun protection practices without worry.

Q7: Does vitamin D help prevent melanoma?

The relationship is complex. Low vitamin D is associated with worse melanoma outcomes in observational studies, but this likely reflects overall poor health rather than a direct causal link. Importantly, attempting to improve vitamin D status through increased sun exposure would increase melanoma risk far more than any potential benefit. Get vitamin D from supplements and food, and use sunscreen for melanoma prevention.

Q8: Can I take vitamin D if I'm taking other medications?

Generally yes, but some medications interact with vitamin D. Anticonvulsants, glucocorticoids, and some anti-rejection drugs can interfere with vitamin D metabolism. If you take medications regularly, ask your doctor whether vitamin D supplementation is appropriate for you.

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Key Takeaways

Vitamin D is essential for skin barrier integrity, immune function, and protection against oxidative damage. Approximately 41.6% of US adults are deficient, with rates as high as 82% in Black Americans. The pathway from sun exposure to vitamin D synthesis is real, but it's also the same pathway that leads to skin cancer—an unacceptable trade-off.

The solution is elegant: get vitamin D from food and supplements, which carry no cancer risk, and use sunscreen to prevent melanoma and non-melanoma skin cancers. In winter months at Kansas's latitude, supplementation is essential. During summer, modest sun exposure (protected with sunscreen after the first 15 minutes) provides incidental vitamin D synthesis while maintaining cancer protection.

Low vitamin D has been associated with worse outcomes in melanoma and inflammatory skin diseases, but attempted supplementation to improve melanoma outcomes has not been successful, suggesting vitamin D deficiency is a marker of poor health rather than a direct cause. Maintaining adequate vitamin D levels supports overall skin health and immune function—and it's easily achievable without skin cancer risk.

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Medical Disclaimer

This article is for educational purposes and should not replace professional medical advice. If you have concerns about vitamin D deficiency, skin cancer risk, or any skin condition, consult a board-certified dermatologist or your primary care physician. Individual vitamin D needs vary based on age, skin tone, location, medical conditions, and medications. Testing and personalized recommendations from your healthcare provider are always appropriate.

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References

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2. Gatta E, Cappelli C. Sunscreen and 25-Hydroxyvitamin D Levels: Friends or Foes? A Systematic Review and Meta-Analysis. Nutrients. 2025;14(2):432. PMID: 40246233.

3. Timerman D, McEnery-Stonelake M, Joyce CJ, et al. Vitamin D deficiency is associated with a worse prognosis in metastatic melanoma. Oncotarget. 2016;7(51):84448-84458. PMID: 28036288.

4. Tran V, Duarte Romero BL, Andersen H, et al. Effect of daily sunscreen application on vitamin D: findings from the open-label randomized controlled Sun-D Trial. Br J Dermatol. 2025;192(4):585-597. PMID: 40927943.

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7. De Smedt J, Van Kelst S, Janssen L, et al. High-dose vitamin D supplementation does not improve outcome in a cutaneous melanoma population: results of a randomized double-blind placebo-controlled study (ViDMe trial). Br J Dermatol. 2024;191(6):886-896. PMID: 38913652.

8. Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab. 1988;67(2):373-378. PMID: 2839537.

9. Schwalfenberg GK, Whiting SJ, Wolever TMS. A review of the critical role of vitamin D in the immune system with emphasis on its role in the control of infections. Nutr Rev. 2013;71(8):438-452. Related to vitamin D immune function and skin barrier physiology.

10. Reichrath J, Lehmann B. The vitamin D receptor in dermatology: new insights into the pathogenesis of actinic keratosis, basal cell carcinoma, squamous cell carcinoma, and melanoma. Adv Exp Med Biol. 2020;1268:285-304. Related to vitamin D signaling in skin cancer prevention and photoprotection.