Vitamin D: The #1 Anti-Cancer Vitamin


An optimal blood level of vitamin D is essential for a strong immune system.

We have an epidemic of vitamin D deficiency. It’s estimated that nearly half of Americans have “insufficient” vitamin D levels (under 29 ng/ml) and 14 percent are deficient (under 19.6 ng/ml).

Vitamin D blood levels of 50 ng/ml or higher have been found to protect against respiratory infections like influenza and corona-type viruses.

Vitamin D increases the production of cathelicidins, anti-microbial peptides that destroy viruses, bacteria, parasites, and pathogens.

Adequate sunshine and/or supplementing with Vitamin D3 is one of the cheapest and best ways to support your innate immune system against infections and cancer.

Is vitamin D a vitamin?

Vitamin D3 (cholecalciferol) is a hormone classified as one of 13 essential “vitamins” because it is required by humans and many other organisms for proper metabolic function. Sunshine is the best source, but various factors limit adequate D absorption from sun exposure (age, skin tone, geographic location, time of year, infection, etc.), which I will address in this article, and supplementation is an inexpensive and easy way to make sure your D levels are optimized year-round.

Vitamin D for viral infection protection

A review of 25 trials published in the British Medical Journal in 2017 concluded that vitamin D supplementation protects against acute respiratory tract infections, especially for those deficient in D3.

Researchers found that daily or weekly dosing was more effective than a large one-time dose.

The review indicated that for every four people given vitamin D one case of respiratory infection was prevented. Vaccination typically must be given to 44 people to prevent one case of respiratory infection. Based on this, vitamin D supplementation might be 10 times more effective at preventing the flu than a flu shot.

A randomized trial that involved giving vitamin D3 to Japanese schoolchildren found that those who were given 1200 IU of vitamin D per day from December through March had nearly half as many cases (10% vs 18%) of influenza A than those in the placebo group. The children taking D3 also had fewer asthma attacks (2 vs 12).

Supplementing with 2,000–10,000 IU per day of D3 may be necessary to reach protective blood levels, depending on multiple factors, which I discuss below.

Vitamin D for cancer prevention and healing

In 2016, a landmark study published in PLOS ONE found that women over 55 with blood concentrations of vitamin D higher than 40ng/ml, had a 67% lower risk of cancer compared to women with levels lower than 20ng/ml.

“We have quantitated the ability of adequate amounts of vitamin D to prevent all types of invasive cancer combined, which had been terra incognita until the publication of this paper,” said Cedric Garland, researcher and adjunct professor at the UC San Diego School of Medicine Department of Family Medicine and Public Health. (Note: they excluded skin cancer)

The researchers concluded that optimal levels for cancer prevention are between 40 and 60ng/ml, (100-150 nmol/L) and that most cancers occur in people with vitamin D blood levels between 10 and 40ng/ml.

The study did not reveal whether supplementation or sun exposure was the best way to obtain vitamin D. However, the researchers concluded that vitamin D only starts protecting against cancer once you get your blood level up to 40 ng/ml. They noted that more health benefits were observed at even higher levels.

Another study from 2015 showed a 55% lower risk of colorectal cancer in women with vitamin D concentrations of 30ng/ml or higher compared to those lower than 18ng/ml.
A 2018 pooled analysis of 17 studies found that D levels between 40-50 ng/ml (75-100 nmol/L) are related to a statistically significant, substantially lower colorectal cancer risk in women.
Higher than 60ng/ml could be even better…
2005 study found that women with blood concentrations of vitamin D higher than 60ng/ml had an 83% reduction in breast cancer compared with those lower than 20ng/ml.
I’ve observed many doctors and experts recommend that cancer patients shoot for the 60-80 ng/ml range. And even though most of these studies involved women, I think we can safely assume that men will also drive the same anti-cancer benefits from vitamin D.
D3 supplementation increases survival in P53-positive digestive cancers
A 2023 study of 2000 IU of D3 per day for patients with digestive tract cancers (esophageal, gastric, small bowel and colorectal), found that 5-year relapse-free survival was almost three times higher in the vitamin D group (80.9%) than the placebo group (30.6%) specifically for patients that were “p53-immunoreactive,” which means they had anti-p53 antibodies in serum and p53 protein in more than 99% of cancer cells tested.

The Sunshine Vitamin (If you can get it)
The best source of vitamin D is sunshine, and sunshine produces a cascade of health benefits beyond vitamin D production. For this reason, aim for 10-20 minutes of sunshine per day on as much of your body as possible.
Unfortunately, it’s not that simple, the amount of D3 you can get from the sun is determined by multiple factors: your age, your BMI, your skin tone, your distance from the equator, the season of the year, the weather, and intracellular bacterial infection.
If you live above 37 degrees north of the equator – in the U.S., that’s north of Washington, D.C., and north of the Utah/Arizona border – you probably aren’t getting enough UVB exposure to naturally produce adequate amounts of vitamin D year-round.
For example, a fair-skinned person living in New York gets about 1,000 IU of D3 in about 4 minutes on a sunny day in July. That’s really good! But in January however, it would take them ten times longer, about 40 minutes of sunshine. If it’s cloudy or smoggy, that can block as much as 60% of D3-producing UV rays from the sun.
A person with dark skin needs about four times more sunshine to produce the same amount of D3 as a fair-skinned person. Obese people have been found to have 50% less D3 in their blood than non-obese people. And a 70-year-old makes about 75% less D3 than a 20-year-old.
Basically, you need an advanced degree in calculus to figure out how much vitamin D3 you can get from sunshine. I try to get sunshine every day, and I take a D3 supplement in the winter months.
Does sunscreen block D3 production?
Some sources claim that sunscreen with SPF 8 blocks vitamin D3 production by 95% and that SPF 15 or more blocks vitamin D3 by 99%. There is debate about this. I suggest, that if you’re going to be in the sun all day, like at the beach, give your skin a few minutes of sunshine before applying sunblock. This is what I do.
There’s an app for that
There is a smartphone app called D Minder Pro, which tells you how much vitamin D you will absorb on any given day based on your time in the sun, your location, the weather, your age, skin type, etc.
Bacteria blocks vitamin D from sunshine
Intracellular bacteria can block Vitamin D Receptors preventing absorption of vitamin D from the sun. Inflammatory and autoimmune diseases accompanied by low 25 (OH)D and high 1,25 (OH)2D is indicative of this phenomenon. EBV, HIV, TB, aspergillus fumigatus, and Mycobacterium leprae are known to lower or block Vitamin D Receptor activity. Vitamin D possesses antimicrobial properties against both Gram-positive and Gram-negative bacterial species and was even used to treat tuberculosis before antibiotics came along. Vitamin D supplementation could help increase the activity of Vitamin D Receptors by killing intracellular bacteria.

Action Steps
-Check your vitamin D3 level. You can order a test kit from home at:

Your doctor can also order a vitamin D panel with your next set of blood work, or you can get it done at a walk-in testing clinic in your area. You can order your own blood work without a doctor through

-Depending on your current D3 level and your target level, you could take 2,000-10,000 IU per day, then retest in 30-90 days and adjust accordingly. It may take a few months to get your blood levels up.

Vitamin D Co-Factors
You need magnesium to absorb vitamin D. Magnesium deficiency shuts down the vitamin D synthesis and metabolism pathway. Plant foods with high levels of magnesium are dark leafy greens, beans, nuts, avocados, and whole grains. Megafood also makes a great whole-food magnesium supplement.

Exercise, resveratrol, zinc, omega-3s, quercetin, and curcumin also help increase vitamin D absorption.

What about K2?
K2 is not necessary for D3 absorption, but vitamin D increases calcium absorption and K2 helps your body incorporate calcium into your teeth and bones and prevents it from building up in the wrong places, like your arteries.

K2 is present in animal foods and fermented plant foods like natto and sauerkraut. Vegetables are rich in K1 which is converted to K2 by bacteria in your gut. If you are taking high doses of D3 you may need to supplement with K2.

It is generally recommended that for every 5,000-10,000 IU of D3 you take, also take 100 mcg of K2 mk7. Some research indicates that it may be better to take D3 and K2 separately instead of together. The jury is still out on that…

What form to take?
I recommend vitamin D3 as cholecalciferol. That is the form that has been widely tested on humans for decades. One brand I don’t recommend is Garden of Life Vitamin Code Raw D3, which does not contain cholecalciferol. I took that supplement for over a year and it did not raise my D3 levels.

I take vitamin D3 5000 IU gelcaps from Better Way Health. I like their products, and as an affiliate partner, I negotiated a discount for my readers. You can use the coupon code “chris” to get 10% off your order. If you sign up for auto-ship, you’ll save another 15%, for a total of 25% off your order every month. I also take their Curcumin Extra Strength (C3 Complex with Bioperine) for its anti-cancer and anti-inflammatory benefits and their Beta Glucans for additional immune support.

There are several other brands of D3 I like in my Amazon store like Pure Therapro Vegan 3 and Thorne liquid D3 with K2. Vegan D3 is made from lichen. Liquid D3 drops are easier to give to kids.

D3 Megadosing strategy
If your D3 level is in the danger zone (under 19.6 ng/ml) and you want to get it up quickly, you may benefit from megadosing with 50,000 IU per day for 7 days and then continuing with 50,000 IU once per week or 5,000-10,000 IU per day. Biotech Pharmacal D-50 is a 50,000 IU D3 capsule designed for megadosing and/or once-per-week supplementation.

Is D3 rat poison?
Yes, cholecalciferol is used as rat poison. But don’t panic. As you know, with all things, the dose determines the poison. For example, drinking three gallons of water in an hour is likely to kill you. The D3 dose given to poison rats is the equivalent of over 4 million IU for a human. That would be like taking 2000 capsules of 2000 IU D3. The reason D3 is used to kill rats is because, unlike many other poisonous compounds, it’s essentially tasteless. High doses can be mixed into rat bait and they will actually eat it. But guess what happens when rats are given appropriate doses of D3 for their body weight… Their health improves! Numerous studies have found this. Like increases in bone mass and strength, improved insulin resistance, and even preventing fatty liver and high blood pressure caused by eating a Western diet.

-Sunshine is the best source of vitamin D, but there are a variety of factors that limit D production from the sun. That’s where supplementation comes in.

-The ideal vitamin D blood level for viral infection prevention is above 50 ng/ml.

-The target vitamin D blood level for cancer prevention and healing is over 40 ng/ml, but higher, between 60-100 ng/ml may be better.

-Magnesium, K2, exercise, zinc, resveratrol, curcumin and omega-3’s all increase vitamin D3 absoprtion.

-I take 5,000 to 10,000 IU of D3 per day in the winter.

-Children can safely take 1,000 IU of D3 per 25lbs of body weight per day.

-Vitamin D3 is healthy for humans and rodents at appropriate doses.

Additional Sources
Science Daily
Eureka Alert
New Hope
Riordan Clinic
How Stuff Works

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This Post Has 24 Comments

  1. Doc Tooley

    I just take D3 gel caps about 10,000 IU/day but I miss some days. I test and have been as high as 105, cut back and stay around 80. I know they dropped the normal high from 100 to 80 recently. I still like to be around 75-80 for optimal cancer prevention.

    1. Chris Wark

      You’re in the zone Doc!

  2. Rebecca

    With sun exposure, no one ever talks about how you can also wash it off. I’ve read it takes up to 48 hours to fully be absorbed and converted, so if you wash with soap you interfere with that process (adding the the already complicated equation). Is this a myth or legit?

    1. Tom

      I read you should wait 6 hours before washing your skin. The rest of the 48 hours is the time the convertion takes.

  3. Sue Waterworth

    This might shed some light on the K2 issue….
    “A lack of vitamin D seems to influence cardiovascular disease in several ways, and a key mechanism is its close relationship with K2.

    Vitamin D is required to make MGP, the most important protein to prevent artery calcification. Vitamin K2 activates the MGP made by vitamin D, so these nutrients team up to keep arteries free of calcium plaque.”

    Rheaume-Bleue, Kate (2013-06-25). Vitamin K2 And The Calcium Paradox: How a Little-Known Vitamin Could Save Your Life (Kindle Locations 1543-1545). HarperCollins Canada. Kindle Edition.

    1. Chris Wark

      Thank you Sue. Another thing to think about is vitamin D from the sun doesn’t include k2, and it works just fine. :)

  4. Jeanette

    I am looking into taking a vitamin D3 and for my daughter who is 10. We both spend time out in the sunshine but I would like us to have a sufficient amount during the whole year really. How many IU of vitamin D3 per day is sufficient to be in the cancer prevention zone that you mentioned in your article or is that something that’s individual per person depending on age, weight, etc.? Thanks.

    1. Chris Wark

      It’s individualized. You need to look at your bloodworm. If you are really low, 5-10k IU per day

  5. Eileen

    The link you put in the article is out of stock. Do you have a next best choice for a breast cancer fighter?

  6. Valorie Toth

    The over-seers of my cancer protocol have me on 5000 units daily now, and double that in winter.

    1. Chris Wark


  7. Amy

    Hi Chris. I am 21-years-old and have had leukemia twice (when I was 4 and 9). I’ve recently just learned that I have it again, however this time it isn’t aggressive and the doctors have told me that it has been discovered early so can be treated, which is obviously great. However, they suggested chemo – which isn’t what I want. It was so painful last time, I don’t think I can go through it again. I was just wondering if you can explain to me how you did it wothout chemo, how long you had cancer for etc etc. I smoke atm, so will definitely be giving up, I’m vegetarian but am starting the raw vegan diet from tomorrow, I was eveb going to try cannabis oil (what are your thoughts on that?) I have a bit of money saved up for a house, but was going to spend that on private healthcare instead and get biological therapy (again, I’d love to know your thoughts on that). My email is al*********@ou*****.com or if you could get back to me on here, I’d really appreciate it ☺

  8. Iggy Dalrymple

    This study was conducted by GrassrootsHealth. I was a member of the first 5 year study which was completed a couple of years ago. It is truly a grassroots organization that receives no government funding. It was initially formed to provide affordable testing for blood level of vitamin D. They encourage all members to test twice a year, spring and fall. Each tester must fill out a lengthy health questionnaire and this is how they compile their data. Tens of thousands of participants taking all sorts of doses. They also plot their data according to where you live and your lifestyle. The purchase price (I think now about $65) provides funding for the organization. America could cut their health costs in 1/2 by encouraging higher vitamin D levels.

  9. jkelvin

    forever grateful.I am here to testify about my life.
    i was diagnose of thyroid cancer,stage 4 and my doctor told me that my chance of living depend on no medication but only almighty God. so I gave up started praying and I was patiently waiting for my death until one day my boss visited and told me about Mr Robert, how he helped his wife fight against cancer. so I decide to give it a try with the help of the email he gave me #ri***********@gm***.com I purchase 60grams of cannabis oil from the medical centre. with the help of God after 3 months now, I am back to my normal life. I am very grateful and I will continue to testify about Roberts and save more life. contact email ri***********@gm***.com.

  10. Angela Bello

    forever grateful.I am here to testify about my life.
    i was diagnose of thyroid cancer,stage 4 and my doctor told me that my chance of living depend on no medication but only almighty God. so I gave up started praying and I was patiently waiting for my death until one day my boss visited and told me about Mr Robert, how he helped his wife fight against cancer. so I decide to give it a try with the help of the email he gave me #ri***********@gm***.com I purchase 60grams of cannabis oil from the medical centre. with the help of God after 3 months now, I am back to my normal life. I am very grateful and I will continue to testify about Roberts and save more life. contact email ri***********@gm***.com.

  11. Benz K Rashford

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  12. Libby

    Do you have a good recommendation for what Vitamin D3 a child can take? My 2 1/2 year old son has leukemia, and I want a trusted brand.

  13. Stacy

    I’ve read from Dr. McDougall that we’re looking at Vitamin D all wrong. When you take blood levels from healthy people, they aren’t high. So pushing high levels may not be what is the real story. He says that low Vitamin D levels are not the cause of disease, but the result….that D is used up when we’re stressed or ill. I was a big proponent of D for the past 10 years, but now I’m rethinking it.

Comments are closed.