Can Vitamin D Reduce Risk of Breast Cancer?

We heard a lot about vitamin D during the beginning of the COVID-19 pandemic. It was a significant finding, early on, that those with low vitamin D levels had a much higher risk of complications with COVID.

First, let’s get a good understanding of what vitamin D is. It isn’t actually a “vitamin”,  it’s a group of fat-soluble secosteroid, a form of steroid hormone.

The skin naturally produces Vitamin D3, cholecalciferol, because UVB rays act on cholesterol in the skin creating a thermal reaction.  I’ve often cautioned people about getting their cholesterol too low, we need it to make vitamin D!

This D now travels to the liver where it becomes 25-dihydroxy vitamin D (calcidiol).  When we are measuring D in the blood, we are measuring the level of calcidiol in the blood to determine one’s “vitamin D level.”

What is the ideal level?  There is much controversy on this one.  What they are seeing with COVID is levels below 20 ng/mL (50 nmol/L) you are at severe risk of life-threatening complications, and those at or above 60 ng/mL (150 nmol/L) recover much quicker.  Your general practitioner is usually looking for a level of 30ng/mL to 40mg/mL on blood work.

Are Vitamin D Levels Key in Preventing Cancer?

There’s been an ongoing debate over the past number of years as to whether or not vitamin D is helpful in preventing cancer, and to what extent. Now new research supports that postmenopausal women with higher levels of vitamin D (≥60 ng/ml) have a much lower risk of breast cancer than women with low blood serum levels (<20 ng/ml) of vitamin D.  Interesting, the same numbers we are seeing with COVID!

There was a study done by the University of California, San Diego School of Medicine, with help from specialists from Creighton University in Omaha, NE, the Medical University of South Carolina in Columbia, and the nonprofit organization GrassrootsHealth in Encinitas, CA.  The study focused on two randomized clinical studies and a prospective cohort.

Researchers looked at post-menopausal women over the age of 55 who were all cancer-free at the beginning of the trial.  The researchers followed the health of these women for four years and monitored for any potential signs of breast cancer.

The two trials contained 3,325 participants between them, and all drew research from a prospective cohort study with an additional 1,713 participants. There were 77 new cases of breast cancer among all the study participants.

Researchers discovered that there was an 82% lower incidence rate of breast cancer in women with 25(OH)D concentrations ≥60 versus those with levels under 20 ng/ml.

An earlier study that looked at women in the U.K., found having a vitamin D level above 60 ng/mL resulted in an 83% lower breast cancer risk, which is nearly identical to GrassrootsHealth’s 2018 analysis.

Cancer cells survive by exploiting cellular differentiation; proliferation; and apoptosis, angiogenesis, and metastasis. UVB exposure and vitamin D reduce the risk of about 15-20 endothelial cancers.  The evidence is strongest for colorectal and breast cancer. People with vitamin D levels above 30 ng/mL tend to live much longer after a cancer diagnosis.

How To Optimize Your Vitamin D Levels

I highly recommend you get tested for your vitamin D levels.  That way you have a much more accurate way of tracking your progress.  There are self-testing kits available if your doctor won’t test (due to insurance paying) or you are not due for an annual lab.  You can order an “at-home” test kit from this site for $79.  

Ideally, we want to get our vitamin D from the sun.  That is not practical during the winter months, but during the summer I encourage you to give it a try.  Lay in the sun with the least amount of clothing on (bikini anyone?) for 15-20 minutes during the peak sun hours of 11 am-2 pm.  Do not wear sunscreen.  Do this at least three days per week.

How much vitamin D do you get during your 20 minutes?  There is something called the Fitzpatrick skin type.  Skin type I is fair skin that always burns, and never tans; type III is darker white skin that burns and tans; type V is brown skin that rarely burns, tans easily.  At noon in Miami, someone with Fitzpatrick skin type III would require 6 minutes to synthesize 1000 IU of vitamin D in the summer and 15 minutes in the winter. So you can see, it depends on your skin type and the time of year, hence getting tested is crucial to really know.


Once you have been tested, depending on your results, you then know how much to supplement with.  If you don’t want to get the test, but want to take a safe amount, 1000IU daily during the winter months would be a good place to start.

Those who came into the hospital with COVID and were low (below<20 ng/ml) were put on massive doses of vitamin D for one week (over 100,000IU daily.)  You may have been prescribed vitamin D by your doctor in the past when your test came up low, and the dosage was very high for a short period of time.  Remember, this is a fat-soluble hormone, so it stores in the body.

Do You Need Vitamin K With Your D?

This question has been asked many times recently.  Most people are taking vitamin D for bone health. Calcitriol helps regulate how much calcium the intestines absorb and the calcium concentration in the blood. Calcitriol acts as a key that can unlock vitamin D receptors, which nearly every cell in the body has.

If you are taking vitamin D for bone health, then yes, it’s important to have “K” on board as well. Vitamin K activates osteocalcin, a protein that promotes the accumulation of calcium in your bones and teeth. Vitamin K also activates matrix GLA protein, which prevents calcium from accumulating in soft tissues, such as the kidneys and blood vessels.

This is a whole other topic, how much calcium should you be taking, and the role of vitamin D and K in calcium absorption.

Food Sources of Vitamin D

Ideally, we should get our “D” from the sun and our food, that is the way our creator made our bodies.  So let’s look at food sources of Vitamin D.

Fish is a great source of D.  Cod Liver oil is rich in vitamin D 400IU per teaspoon.  Salmon, mackerel, sardines, and tuna have anywhere from 1.9 to 5.2 IU’s of vitamin D per serving.

Egg yolks and beef liver are lower at .07 and .05 IU per serving.  Portobello and Crimini mushrooms that have been exposed to ultraviolet light average .11 and .32 IU per serving.



If you would like to do further research on vitamin D, these sites are helpful.


About the Author: Chris McKee

Chris McKee Certified Nutritionist and Certified Diet Counselo

Chris McKee is a Certified Nutritionist and Certified Diet Counselor with over 30 years of experience in whole-food cooking, healthy lifestyle coaching, individual nutritional counseling and speaking to 1,000’s of people about the role of good nutrition in preventing disease.

Chris is also a Certified Nutragenomix practitioner and this allows her to look deep into your genetic profile and personalize your nutrition program based on your unique genetic fingerprint.

She runs on-line courses including her 10 Day Clean Eating Challenge, 21 Days Prepping for the Keto Diet as well as her Hope 4 Cancer Recovery program.

Chris and her husband Ed love to travel, hence the name “The Nomadic Nutritionist”.  She is a grandmother of four and a great-grandma of two!  She loves to cook, explore new food finds, hike and fish.

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