Vitamin D is often an overlooked therapy for both treating and preventing cancer.
Deficiency is common in cancer patients, often stemming from limited sun exposure, inadequate nutrition, chronic inflammation, and impaired liver or kidney function, all of which disrupt the body’s ability to properly activate and use it.
The active form of vitamin D has multiple anti-cancer effects. Mechanistically, vitamin D helps regulate cell differentiation, inhibit uncontrolled proliferation, reduce inflammation, and support immune surveillance, all of which are essential for preventing cells from becoming cancerous.
A pooled analysis found that those with a serum level of 25 (OH) D of about 52 ng/ml had a 50% lower risk of developing breast cancer than those with serum <13 ng/ml.
There’s a large body of evidence that suggests low vitamin D levels increase the risk of developing certain cancers, especially breast, colorectal, prostate, and pancreatic cancers.
So while vitamin D deficiency removes a layer of protection, increasing vulnerability to cancer-promoting factors (like DNA damage, inflammation, and immune dysfunction).
Cancer itself, and especially cancer treatments, can reduce vitamin D levels through reduced sunlight exposure, poor nutrition, liver/kidney dysfunction, inflammation, and altered metabolism.
For instance, a Spanish study found a high prevalence of vitamin D deficiency among recently diagnosed cancer patients, particularly in colorectal and head and neck cancers. The study reported that 57.97% of patients showed vitamin D deficiency (<50 nmol/L), and 21.74% had insufficiency (50–75 nmol/L) (Calmarza et al., 2018).
So for many patients, vitamin D deficiency is present before diagnosis, and often worsens after due to treatment-related factors.
Because of this, checking and optimizing vitamin D levels should be a standard part of cancer prevention and care. A simple blood test for 25(OH)D can help determine your status. Some studies suggest higher levels (60–80 ng/mL) is optimal.
Women with even higher vitamin D levels (60 ng/ml or higher) had an 80% lower risk of developing breast cancer compared to those with levels below 20 ng/ml, based on data from over 5,000 participants.
Vitamin D:
- Promotes cell differentiation: One of the most powerful agents for guiding immature cells to fully develop into specialized, functional types. This is essential for maintaining tissue integrity and preventing disordered growth.
- Inhibits excessive cell proliferation: Helps keep cell division in check, reducing the risk of uncontrolled growth that can lead to tumor formation.
- Modulates inflammation: Suppresses pro-inflammatory cytokines and supports the transition toward a more balanced, anti-inflammatory immune state.
- Favors the Th2 immune response: It encourages a shift from the inflammatory Th1 profile to a Th2-dominant response, which supports tissue repair and immune regulation.
- Acts as a membrane antioxidant: Protects cell membranes from lipid peroxidation, preserving the integrity of cell signaling and mitochondrial function.
- Supports hormonal balance: Has been shown to help lower excessive estrogen levels while supporting progesterone production, especially important in hormonally driven cancers.
- Inhibits metastasis: Vitamin D reduces enzymes that break down surrounding tissue (like MMPs), strengthens cell-to-cell adhesion, and interferes with signaling pathways that promote migration and invasion. This makes it harder for cancer cells to detach and form new tumors in other parts of the body.
How to increase vitamin D:
- Spend time in the sun whenever possible without sunscreen (avoid burns). UVB rays are essential for vitamin D synthesis.
- Consider supplementation if sun exposure is limited or your levels are low. I like vitamin D3 (cholecalciferol) best, and usually combine vitamin D3 with vitamin K2 to ensure that calcium is properly directed to the bones and teeth, rather than accumulating in soft tissues like arteries
- Support liver and kidney health. These organs are responsible for converting vitamin D into its active form. A healthy metabolism, adequate magnesium, and low inflammation all support this process.
- Avoid factors that deplete vitamin D like stress and excess body fat, both of which can interfere with vitamin D metabolism and reduce its availability to cells.