An optimal blood level of vitamin D is essential for a strong immune system, disease prevention, and healing.
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 of Americans are clinically deficient (under 19.6 ng/ml).
Vitamin D (25-hydroxyvitamin D) blood levels of 50 ng/ml or higher have been found to protect against respiratory infections like influenza and coronavirus-type viruses.
Vitamin D increases the production of cathelicidins, anti-microbial peptides that destroy viruses, bacteria, parasites, and pathogens.
Adequate sunshine and/or Vitamin D3 supplementation are among the cheapest and best ways to support your innate immune system against infections, cancer, and other chronic diseases.
Is vitamin D actually a vitamin?
Vitamin D3 (cholecalciferol) is a steroid 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, bacteria, 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, like influenza, etc., 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 comparison, 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 received 1200 IU of vitamin D per day from December through March had nearly half as many influenza A cases (10% vs 18%) as those in the placebo group. The children taking D3 also had fewer asthma attacks (2 vs 12).
A study of 1850 patients found that Vitamin D accelerated clearance of drug-resistant tuberculosis when combined with standard antibiotic treatment.
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.
Why Vitamin D Recommendations Are Dangerously Low
For decades, official vitamin D recommendations have been built on a serious statistical mistake. A reanalysis published in Nutrients revealed the Institute of Medicine misread its own data. Researchers used values meant for population averages, not individuals, to set the RDA. As a result, the current recommendation of 600 IU per day leaves most people deficient.
The corrected analysis shows 8,895 IU per day is required for 97.5% of people to reach even a modest blood level of 50 nmol/L. This explains why deficiency remains widespread despite people “meeting” the RDA. Public health guidance failed at the math level, and the consequences show up as reduced immune resilience and increased risk of chronic disease.
Instead of relying on injections and seasonal flu campaigns, public health would benefit far more from deliberate education on sun exposure, outdoor time, and vitamin D testing.
The fix is simple. Get outside. Measure levels. Correct the deficiency.
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 40 ng/ml had a 67% lower risk of cancer compared to women with levels lower than 20 ng/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 determine whether supplementation or sun exposure was the best way to obtain vitamin D. However, the researchers concluded that vitamin D only begins protecting against cancer once your blood level reaches 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 30 ng/ml or higher compared to those lower than 18 ng/ml.
A 2018 pooled analysis of 17 studies found that vitamin D deficiency in men and women increased the risk of colorectal cancer by 31%. Conversely, sufficient levels between 40-50 ng/ml (75-100 nmol/L) were associated with a 19% lower risk of colorectal cancer
A study found Vitamin D supplementation significantly improves treatment outcomes. Patients taking 50,000 units of D3 weekly saw a 233% increase in pathological complete response rates. Incredible results for breast cancer patients
Higher than 60ng/ml could be even better…
A 2005 study found that women with blood vitamin D concentrations above 60 ng/ml had an 83% reduction in breast cancer risk compared with those with concentrations below 20 ng/ml.
I’ve observed many integrative doctors and experts recommending that their cancer patients aim 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 derive 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.
D3 plus immunotherapy increases survival
A 2025 study found that higher vitamin D levels were associated with a 53% improvement in overall survival among cancer patients with solid tumors receiving immune checkpoint inhibitors.
D3 reduces the risk of colitis from immunotherapy
A 2020 study found that patients taking D3 while taking immune checkpoint inhibitors for melanoma had a 54-65% reduced risk of colitis. Vitamin D has also been found to make melanoma cells less aggressive.
Vitamin D can also reduce the gastrointestinal effects of chemotherapy by suppressing inflammation and enhancing T-cell function, thereby increasing immunity.
This study found that cancer patients with insufficient levels of vitamin D prior to treatment with paclitaxel are at higher risk for developing chemotherapy-induced peripheral neuropathy.
In the SUNSHINE trial, patients receiving high-dose vitamin D (8,000 IU/day for two weeks, followed by 4,000 IU/day) combined with standard chemotherapy had a 36% lower risk of disease progression or death during the 22-month follow-up period.
A 2025 study found that breast cancer patients taking 50,000 units of D3 weekly saw a 233% increase in pathological complete response rates.
A 2024 study on 19,000 adults with high blood pressure found that those with vitamin D blood levels less than 25 nmol/L were 97% more likely to die prematurely. Those with levels between 25 and 49.9 nmol/L were 71% more likely to die. However, patients with high blood pressure who took supplemental vitamin D were 25 percent less likely to die. The greatest benefits from D supplementation were observed in those who took higher doses and in those without diabetes or cardiovascular disease.
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 even bacteria in your body.
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 July day. 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, it can block up to 60% of the D3-producing UV rays from the sun.
A study on 10,000 people in Ireland found that 87% were deficient in vitamin D and 75% of them had “detrimentally low levels.” The levels of so many people were so low that the researchers initially thought their equipment was broken!
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 higher blocks vitamin D3 production 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 in the sun before applying sunblock. This is what I do.
There’s an app for that
There is a smartphone app called D Minder Pro that estimates how much vitamin D you will absorb on any given day based on your time in the sun, location, weather, age, skin type, etc.
Bacteria can block vitamin D from the sun
Intracellular bacteria can block vitamin D receptors, preventing the absorption of vitamin D from sunlight. Inflammatory and autoimmune diseases accompanied by low 25(OH)D and high 1,25(OH)2D levels are 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: https://grassrootshealth.net/project/daction/
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 www.yourlabwork.com
-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
Magnesium deficiency shuts down the vitamin D synthesis and metabolism pathway. Magnesium optimizes vitamin D levels, raising it in people with deficient levels and lowering it in people with high levels. Plant foods high in magnesium include 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?
Technically, 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.
Vegetables are rich in K1, which is converted to K2 by bacteria in your gut. K2 is present in animal foods and fermented plant foods like natto and sauerkraut. 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 suggests it may be better to take D3 and K2 separately rather than 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 5,000 IU gel caps 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 immune support.
There are several other D3 brands I like in my Amazon store, such as 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, 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.
I read online that “D3 is rat poison!”
This is a half-truth. Cholecalciferol is used as rat poison, but don’t panic. As you know, with all things, the dose determines the poison. And you can poison yourself with water. There have been multiple cases of people dying from hyponatremia, which is water intoxication (Google it). The D3 dose given as poison to rats is the equivalent of over 4 million IU for a human. That would be like taking 2,000 capsules of 2,000 IU D3 at once. The reason cholecalciferol is used to kill rats is that, unlike many other poisonous compounds, it’s essentially tasteless. Super 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 that giving rodents D3 increases their bone mass and strength, improves insulin resistance, and even prevents fatty liver and high blood pressure induced by feeding them a high-fat, high-sugar diet.
BIG TAKEAWAYS
-Sunshine is the best source of vitamin D, but there are a variety of factors that limit D production from the sun, especially in winter. That’s where supplementation helps.
-The ideal vitamin D blood level for cold/flu/covid prevention is above 50 ng/ml.
-The target vitamin D blood level for cancer prevention and healing is also over 50 ng/ml; between 60-100 ng/ml may be more beneficial.
-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
NIH
Science Daily
Eureka Alert
New Hope
Riordan Clinic
How Stuff Works
…
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This Post Has 24 Comments
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.
You’re in the zone Doc!
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?
I read you should wait 6 hours before washing your skin. The rest of the 48 hours is the time the convertion takes.
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.
Thank you Sue. Another thing to think about is vitamin D from the sun doesn’t include k2, and it works just fine. :)
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.
It’s individualized. You need to look at your bloodworm. If you are really low, 5-10k IU per day
The link you put in the article is out of stock. Do you have a next best choice for a breast cancer fighter?
The over-seers of my cancer protocol have me on 5000 units daily now, and double that in winter.
Perfect!
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 [email protected] or if you could get back to me on here, I’d really appreciate it ☺
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.
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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 #[email protected] 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 [email protected].
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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.
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.
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