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Story at-a-glance

• A study conducted by researchers from the University of Finland found that melanoma risk dropped by nearly 50% with consistent vitamin D supplementation, even among individuals with high-risk skin types or previous melanoma diagnoses
• The protective benefits of vitamin D occurred regardless of measured blood levels, suggesting consistency in supplementation might matter more than test results when it comes to reducing melanoma risk
• Vitamin D sufficiency was linked to thinner melanoma tumors and better survival, with even small increases in blood levels providing measurable improvements in relapse-free outcomes
• Vitamin D influences how your cells grow, repair, and die, helping prevent cancer by activating receptors that suppress tumor growth, reduce DNA damage, and support healthy immune responses
• Safe sun exposure, not just supplements, is a vital vitamin D source, especially when paired with reduced seed oil intake and enhanced skin protection strategies like astaxanthin and niacinamide

The National Cancer Institute estimates that around 104,960 new melanoma cases will be diagnosed this year, and 8,430 people will succumb to this disease.1 It's the most dangerous type of skin cancer — it often starts from a simple mole or freckle that changes shape, color, and size, then spreads and becomes life-threatening.

As a result, many people started avoiding the sun, thinking it would help reduce their risk of this aggressive form of cancer. However, by doing so, they are also being deprived of a powerful nutrient that will help reduce melanoma risk — vitamin D.

A Healthy Vitamin D Status Is Strongly Linked to Reduced Risk of Melanoma

A recent study published in Melanoma Research investigated whether taking vitamin D supplements on a regular basis was linked to a lower risk of developing melanoma. Conducted by researchers at the University of Eastern Finland in the North Savo Skin Cancer Programme, the study examined 498 adults with a risk for skin cancers like melanoma, basal cell carcinoma, and squamous cell carcinoma to figure out whether vitamin D supplementation could play a role in preventing these diseases.2,3,4

• The participants have a history of abnormal moles or other skin abnormalities — They included both men and women; some had already been diagnosed with melanoma in the past, while others had precancerous skin changes. They were divided into three groups according to their self-reported vitamin D use — Regular users, occasional users, and non-users.

• Those who regularly took vitamin D had a significantly lower risk of melanoma than non-users — Even among those who had other risk factors, this simple daily habit seemed to make a noticeable difference. Among regular vitamin D users, only 18.1% had a current or previous diagnosis of melanoma, but in the non-user group, that number jumped to 32.3%. That's a nearly 50% reduction in melanoma risk simply based on whether someone consistently took this one nutrient.

• Even those who took vitamin D occasionally have a lower risk — However, the researchers did not find significant links between vitamin D intake and the severity of photoaging, facial photoaging, actinic keratoses, basal cell carcinoma, and squamous cell carcinoma.

Even participants with a weakened immune system decreased their risk of this type of skin cancer when they regularly took vitamin D. According to MindBodyGreen:

"This research suggests that regularly maintaining healthy vitamin D status may decrease your chance of developing melanoma, but scientists still aren't sure why … While further evidence is needed to understand exactly how your vitamin D status affects your risk of developing skin cancer, there is no denying the importance of this vitamin."5

• This protective effect showed up regardless of blood levels — To put it simply, it didn't matter if someone's lab test showed they had "adequate" levels of vitamin D in their blood. What mattered more was whether they reported regular use of a vitamin D supplement. Ilkka Harvima, a professor of Dermatology and Allergology and one of the study authors, said:

"Earlier studies back our new findings from the North Savo region here in Finland. However, the question about the optimal dose of oral vitamin D in order for it to have beneficial effects remains to be answered. Until we know more, national intake recommendations should be followed."6

Regular, Consistent Vitamin D Intake Is Key to a Lower Cancer Risk

Calcidiol, also known as 25-hydroxyvitamin D (25(OH)D), is the primary storage form of vitamin D in your body and the form measured in blood tests to assess your vitamin D status. Calcidiol is subsequently converted in your kidneys and other tissues to the active hormonal form, 1,25-dihydroxyvitamin D (1,25(OH)2D), also known as calcitriol.

While the featured study didn't find any link between calcidiol blood levels and protective effects against cancer, previous studies have found notable associations. For example, a review published in Anticancer Research analyzed prior studies to determine what level of calcidiol is truly protective.7

• It's not as simple as "more is better" — In fact, both low and high levels of calcidiol may increase your risk — meaning the key is keeping your vitamin D levels within a healthy range.

The review found evidence suggesting that while low calcidiol levels are linked to a higher risk for many cancers, very high levels were actually associated with increased rates of certain cancers, including pancreatic and esophageal. This challenges the long-standing assumption that cancer risk drops continuously as vitamin D levels rise.

• Instead, the researchers proposed a U-shaped relationship — Your risk goes up when levels are either too low or too high, and there's a "sweet spot" in between where your risk is lowest.

• However, take note that there's a lot of controversy over taking higher doses of vitamin D — This is because excessive vitamin D, particularly in combination with lack of vitamin K2 and magnesium, may cause overabsorption of calcium, which in turn may result in calcium deposits in your heart and kidneys.

Personally, I strongly disagree with high-dose therapy as it is unnecessary and non-biological and if you are supplementing, I would recommend taking it once a day. What I do advise instead is to meet — and stay within — the optimal levels (more on this later).

However, what links this earlier study to the Finnish research is its focus on consistency. Regular vitamin D users had significantly fewer melanoma cases — even when their calcidiol levels didn't seem to explain the difference. This supports the idea that stable, balanced calcidiol levels — not extreme highs or lows — are what truly matters for preventing cancers like melanoma.

Melanoma Patients Were Found to Have Lower Vitamin D Levels

The featured Finnish study was not the first to examine the link between melanoma and vitamin D deficiency. An earlier study published in Molecular Oncology, conducted by researchers at the University of Leeds, investigated findings from lab studies, animal models, genetic investigations, and human epidemiological data to reveal how vitamin D might influence both the development and the outcome of melanoma.8

• The study focused on individuals with melanoma and the severity of their disease — The researchers looked at whether the participants' vitamin D levels at the time of diagnosis played a role in how aggressive their cancer was — and how likely it was to come back.

• People who had higher vitamin D levels at diagnosis tended to have thinner tumors and better survival outcomes — Specifically, patients with serum levels above 65.6 nmol/L (26.3 ng/mL) had a lower rate of melanoma relapse compared to those with levels below 48.7 nmol/L (19.5 ng/mL). The relapse-free survival curve showed that only 18% of patients with the highest vitamin D levels experienced relapse, compared to 23% among those with the lowest levels.

• Even a small boost helped — For every 20 nmol/L increase in serum vitamin D, there was a 21% improvement in relapse-free survival (Hazard Ratio: 0.79, 95% CI: 0.64–0.96). That means that going from 50 to 70 nmol/L, for example, could provide a measurable survival advantage.

• Tumor thickness was also inversely correlated with vitamin D levels — Melanoma tumors are measured using the Breslow thickness (or Breslow depth), which indicates how deeply the tumor has grown in the skin. It's a key factor in determining melanoma severity. Thinner tumors are easier to treat and have a much better prognosis.

• The biggest benefits were seen in those who were the least deficient — The researchers found that individuals who had enough vitamin D to start with or who managed to increase their levels to 70 nmol/L or above had the best outcomes. Interestingly, patients with very low levels at diagnosis didn't experience the same protective effect — possibly because the damage was already done, or their levels were too low to activate the necessary biological pathways.

This highlights the importance of prevention and maintenance rather than trying to "catch up" after the fact. If you're managing a melanoma diagnosis — or are at an increased risk, simply ensuring your vitamin D levels are optimal from the outset might improve your odds dramatically.

Vitamin D's Role in Cancer Protection

As I've noted in previous articles, vitamin D is one of the most important nutrients that your body needs to stay optimally healthy. It plays an essential role in your bone health, immunity, and brain function, to name a few. Now, more and more research is showing how it protects against different types of cancer.

• Vitamin D reduces the risk of cancer mortality — A 2023 systematic review and meta-analysis published in Ageing Research Reviews found supplementing with vitamin D3 lowered the risk of dying from cancer by 6%. When the researchers only analyzed studies involving daily vitamin D intake, they found that cancer mortality dropped by a significant 12%.9

• Having optimal levels reduces breast cancer risk — A GrassrootsHealth analysis published in June 2018 in PLOS ONE found that women with a vitamin D level at or above 60 ng/mL (150 nmol/L) had an 82% lower risk of breast cancer compared to those with levels below 20 ng/mL (50 nmol/L).10

• How does this nutrient help with cancer protection? Vitamin D acts by attaching to vitamin D receptors (VDR) found in your cells. When this occurs, a series of signals are released that affect how your cells grow, die and repair themselves.11 However, having poor vitamin D levels weakens these protective effects, allowing abnormal cells to survive and multiply instead.

• Vitamin D's effects on VDR lead to many beneficial effects — In lab and animal studies, the active form of vitamin D was shown to reduce DNA damage after UVB exposure, prevent cell death in skin cells, slow down tumor grown and metastasis in some melanoma cell lines, and increase cell differentiation, allowing them to behave more normally.12

• VDR also inhibits MAPK signaling — This is a cell-signaling system that is typically hyperactive in melanoma cells. It does this by suppressing epidermal growth factor receptor pathway (EGFR), a pathway that is upregulated in melanoma.13

What's the Best Way to Get Vitamin D?

While the previous research focused on getting this nutrient from supplements, I do believe that safe daily sun exposure — emphasis on "safe" — is still the best option for optimizing your vitamin D levels. When sunlight hits your skin, it turns a substance in your body into vitamin D3.

Of course, with melanoma being strongly associated with sunburn, many people would hesitate to bare their skin to the sun, especially if their risk for this type of disease is already high. The key here is to do it safely and in moderation.

• To gauge safe sun exposure, perform a simple "sunburn test" — Pay close attention to your skin as you're in the sun. You're aiming to stay just below the point where your skin starts to turn even slightly pink. Any redness at all is a signal to get out of the direct sun, so avoid getting a sunburn.

• Before you get sun exposure during peak hours, eliminate all seed oils from your diet — Seed oils are packed with linoleic acid (LA), which then accumulates in your skin. When the LA in your skin interacts with the UV rays from the sun, it oxidizes and triggers inflammation, DNA damage, and sunburn — possibly increasing your melanoma risk. To avoid this, I recommend avoiding direct sunlight during peak hours until you've eliminated seed oils for at least six months.

One of the best ways to keep track of your LA intake is to download my Mercola Health Coach app, which will be officially released this year. One of its main features is the Seed-Oil Sleuth, which calculates your LA intake to the tenth of a gram. It's a helpful way to keep track of your seed oil consumption, to ensure that you're slowly but surely reducing your intake.

 

• A faster way to purge LA from your skin — I recently discovered that consuming pentadecanoic acid or C15:0, a special fat found in raw grass fed milk, helps purge LA embedded in your skin faster. Taking 250 mg daily may help shorten the time it takes for your skin to safely interact with sunlight again, but emerging research suggests much larger doses may be even better.14

• More protective measures to consider — In some cases, it's impossible to completely avoid peak sunlight during the period when you're purging LA from your diet. To protect yourself, I recommend these strategies:

◦ Take 12 milligrams of astaxanthin daily — This will enhance your skin's UV resistance.

◦ Apply niacinamide (vitamin B3) cream before and after sun exposure.

◦ Take a baby aspirin — This will help prevent LA from converting to harmful oxidized linoleic acid metabolites (OXLAMs). Ideally, take the aspirin 30 minutes to one hour before sun exposure.

• What's the optimal level for cancer prevention? While the studies mentioned above suggested vitamin D levels, I believe they are still insufficient to provide protective effects against cancer. Ideally, I recommend aiming for between 60 ng/mL and 80 ng/mL. The cutoff for sufficiency is around 40 ng/mL. If you live in Europe, the measurements you're looking for are 150 to 200 nmol/L and 100 nmol/L, respectively.

• Lastly, make sure to get your levels tested — To know if you're getting enough sun exposure or supplementing enough with vitamin D3, I recommend measuring your vitamin D level, ideally twice a year. Once you've confirmed your vitamin D levels via testing, adjust your sun exposure and/or vitamin D3 supplementation accordingly. Then, remember to retest in three to four months to make sure you've reached your target level.

Frequently Asked Questions (FAQs) About Vitamin D and Melanoma

Q: Can taking vitamin D reduce my risk of developing melanoma?

A: Yes. A Finnish study found that regular vitamin D supplementation was linked to nearly a 50% lower risk of melanoma, even in individuals with high-risk skin profiles or a history of abnormal moles. Consistency in use was key to this protective effect.

Q: Does my blood vitamin D level matter, or is supplement use more important?

A: Interestingly, the study found that self-reported regular supplement use correlated more strongly with lower melanoma risk than actual blood levels of vitamin D. This suggests consistent intake may offer protection independent of lab-measured calcidiol levels.

Q: Is there an optimal vitamin D level for cancer prevention?

A: Yes. Research suggests a "sweet spot" for vitamin D levels — too low or too high may increase cancer risk. The ideal range for prevention appears to be between 60 and 80 ng/mL (or 150 to 200 nmol/L), with 40 ng/mL being the minimum threshold for sufficiency.

Q: How does vitamin D help protect against cancer like melanoma?

A: Vitamin D activates receptors in your cells that regulate growth, repair, and immune function. It reduces DNA damage from UV exposure, suppresses inflammatory signals, slows tumor growth, and enhances cell differentiation to keep cells behaving normally.

Q: What's the safest way to increase my vitamin D levels?

A: Safe sun exposure is best — ideally before skin reddening occurs and only after reducing dietary seed oils, which make skin more vulnerable to sun damage. Supplementation is also effective, especially when combined with nutrients like magnesium and vitamin K2.

Sources and References

• 1 National Cancer Institute, Cancer Stat Facts: Melanoma of the Skin
• 2 Melanoma Research, April 2023, 33(2):p 126-135
• 3, 5 MindBodyGreen, June 5, 2025
• 4 Pharmacy Times, January 10, 2023
• 6 Science Daily, January 9, 2023
• 7 Anticancer Res. 2012 Jan;32(1):373-81
• 8, 13 Mol Oncol. 2011 Feb 3;5(2):197–214
• 9, 11 Ageing Research Reviews, June 2023, Volume 87, 101923
• 10 PLoS ONE, June 15, 2018, 13(6): e0199265
• 12 Melanoma Manag. 2015 Feb 25;2(1):51–61
• 14 Clinical Science (1985) 68, 449-454 (Archived)