• This large-scale review looked at diverse populations — The data covered various groups and nationalities, including women in the U.S. Midwest, Danish adults with a family history of cancer, and Canadians living in high-altitude areas. The participants had different health statuses as well — some had colorectal cancer, or a documented vitamin D deficiency. Others were also given a vitamin D supplement.

• While the participants varied in health status and genetic risk, a consistent pattern emerged — The researchers found that the lower your vitamin D levels, the higher your risk of developing colon cancer. On the flip side, people with adequate or optimal levels of vitamin D had dramatically lower rates of cancer.

"Maintaining optimal vitamin D levels and adequate dietary intake is crucial in preventing CRC and improving patient prognosis," the researchers said.

• Unfortunately, majority of people today have very low levels of this vital nutrient — A study that looked at the vitamin D status of more than 5,600 adults found that 37.6% had vitamin D insufficiency (blood levels between 20 and 30 ng/mL), while 42% were severely deficient (blood levels lower than 20 ng/mL) in this nutrient.⁴

• A landmark 1996 study found that women with the highest vitamin D intake had a 58% lower risk than those with the lowest intake.⁶

• A 2021 meta-analysis found a 39% lower risk of colorectal cancer in people with higher blood levels of vitamin D. The researchers also noted that when vitamin D levels were monitored over time, those who maintained higher levels had a 20% lower chance of developing colorectal cancer down the line.⁷

• A Canadian study found that supplementing with vitamin D reduced the incidence of precancerous polyps — by 33% for all polyps and 43% for high-risk ones. These polyps often go on to become cancer if not addressed early, so this kind of intervention has massive implications.⁸

• The Iowa Women's Health study found that women who took vitamin D with calcium saw a 15% drop in colorectal cancer risk compared to those who didn't take any supplements.⁹

• The Danish "Diet, Cancer and Health" study (one of the major ones included) found that vitamin D offered even stronger protection in people with a high genetic risk of colon cancer. That means if you've got a family history of this disease, optimizing your vitamin D status isn't just helpful — it could be life-saving.¹⁰

• Vitamin D's role in cancer protection — Vitamin D acts by attaching to vitamin D receptors (VDR) found in your cells, including your colon cells. When this occurs, a series of signals are released that affect how your cells grow, develop, and survive.¹¹ However, having poor vitamin D levels weakens these protective effects, allowing abnormal colon cells to survive and multiply instead.¹²

• Another vital purpose of vitamin D — Animal studies have also found that vitamin D helps delay some age-related changes by activating another important pathway via the vitamin D receptor. This pathway involves a molecule called Nrf2, which plays a crucial role in protecting your body from oxidative stress and DNA damage — two factors that are commonly linked to the development of cancer.¹³

• Vitamin D also supports the health of your intestinal lining — The colon is constantly regenerating itself, and this requires precise communication between your cells. Vitamin D ensures that this process runs smoothly. According to one research:

"Vitamin D and its nuclear receptor (VDR) regulate intestinal barrier integrity, and control innate and adaptive immunity in the gut. Metabolites from the gut microbiota may also regulate expression of VDR, while vitamin D may influence the gut microbiota and exert anti-inflammatory and immune-modulating effects."¹⁴

• Inhibiting cancer cell growth — It targets different stages of cancer development and progression. This includes the initiation, growth, and spread of cancer cells.

• Preventing cancer spread — It has antimetastatic effects, meaning it stops cancer cells from spreading from the original tumor site to other areas of the body. This is useful for improving survival rates, as metastasis is often responsible for many cancer fatalities.

• Stopping tumor formation — Vitamin D is anti-tumorigenic; it helps prevent tumors from forming or growing by inducing cancer cell death, blocking cell cycle progression, or blocking pathways that trigger tumor growth.

• When sunlight hits your skin, it produces a type of vitamin D called cholecalciferol — It's far different from vitamin D2, which is what you get from plant sources like mushrooms and yeast. D3 is actually more effective at increasing blood levels. On a typical sunny day, your body may produce up to 25,000 international units (IU) of vitamin D.¹⁸

• How much sun is enough? Ideally, you need to expose your bare skin to direct sunlight daily. Gauge how long to stay under the sun safely by doing this simple test — Pay close attention to your skin for any sign of pinkness. The goal is to stay just below the point where your skin starts to turn slightly pink. If your skin turns red, it's a sign of damage, not benefit — get out of the direct sun immediately.

• Your body cannot get too much vitamin D from sun exposure — Your body stops making vitamin D when you've got enough, so you can't overdo it from sunlight alone. However, if you have darker skin, you'll need to spend more time in the sun to produce the same amount of vitamin D as someone with lighter skin.

• An important caveat about sun exposure — If you're still consuming a processed food diet loaded with vegetable oils or seed oils, then sun exposure will work against you. This is because 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 triggers inflammation and DNA damage. To avoid this, I recommend avoiding direct sunlight during peak hours until you've eliminated seed oils for at least six months.

• Additional reminders on sun exposure — In some cases, it's impossible to completely avoid peak sunlight during the period when you're purging LA from your diet. If this is the case, it's best to follow protective measures:

• A strategy to speed up LA removal from your skin — One interesting discovery I made was that there's a way to quicken up the pace by which your body purges LA embedded in your skin. This is by ingesting a special fat called pentadecanoic acid or C15:0, found in raw, grass fed milk.

I recommend getting at least 2 grams of C15:0 per day, which will significantly speed up LA clearance from your body from two to three years to 12 to 18 months. My article, "The Fast-Track Path to Clearing Vegetable Oils from Your Skin" will give you more insightful details about C15:0.

• What's the optimal level for cancer prevention? Ideally, you need to aim for between 60 ng/mL and 80 ng/mL. The cutoff for sufficiency is around 40 ng/mL. In Europe, the measurements you're looking for are 150 to 200 nmol/L and 100 nmol/L, respectively.

• Adjust your levels depending on your test results — 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.

• Optimize other nutrients to help meet your levels — Remember to balance your vitamin D3 with calcium, magnesium, and vitamin K2 through your healthy diet.

• If you're supplementing with vitamin D3, here's a tip — Take it with a meal that has some healthy fat, like grass fed butter or tallow. Since vitamin D is fat-soluble, this will help your body absorb it.