Can vitamin D lower the risk for breast cancer? Yes, it can—maybe. It depends on the form of vitamin D that circulates throughout your body. That form, called vitamin D3 sulfate, is the one that you make when you expose your skin to sunshine. It is not the same as the vitamin D in foods or supplements.

Different forms of vitamin D have their value. They are just not the forms that provide the complete array of health benefits that you get from vitamin D3 sulfate.

How does vitamin D work in the body? The answer depends on which form of the vitamin we are talking about. It is the key to understanding the link between vitamin D and breast cancer awareness.

Let’s take a look to see why that is the case.

Different Kinds of Vitamin D

The most common forms of vitamin D from foods and supplements are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

What foods are rich in vitamin D? First off, vitamin D2 is the main source of dietary vitamin D. It occurs in fatty fish (tuna, salmon, mackerel), beef liver, cheese, egg yolks, and mushrooms. It is also the form of vitamin D that is used to fortify dairy products, orange juice, soy milk, and cereals.

Vitamin D2 is the form that was first discovered to prevent the childhood bone-weakening disease called rickets (2003). It is still used in modern times as a prescription treatment for rickets, for osteoporosis caused by glucocorticoid drugs, for vitamin D deficiency, and for conditions resulting from low levels of parathyroid hormone.

Vitamin D2 is the cheapest form of vitamin D to mass produce, which is why it is still used as a food additive and as a prescription vitamin. However, it is the least absorbable and least effective form of vitamin D.

Vitamin D3 is thought to be more absorbable than vitamin D2. It is derived commercially either from fish oil or from sheep’s lanolin. Sheep’s lanolin contains 7-dehydrocholesterol, which is isolated and converted into vitamin D3.

Both vitamin D2 and vitamin D3 have their greatest impact on calcium metabolism. They help regulate the amount of calcium going into and out of cells.

Vitamin D3 sulfate, the vitamin D that you make in your skin, is the easiest form of the vitamin for body-wide transport. That’s because it is both fat-soluble and water-soluble. Its dual solubility allows it to move freely in blood and to enter cells through their fatty membranes.

A key property of vitamin D3 sulfate is that its production is regulated based on supply and demand. Scientists call this a feedback mechanism. This is a crucial property for maintaining the right amounts of vitamin D in the right places.

We have no such feedback mechanism for vitamin D2 or for unsulfated vitamin D3. Furthermore, we do not have the ability to turn ingested vitamin D3 into vitamin D3 sulfate. Except for mother’s milk, including unpasteurized cow’s milk, there are no dietary sources for vitamin D3 sulfate. You can get it only by making it in your skin.

The source of vitamin D is the key factor in determining whether this vitamin can provide benefits against breast cancer.

Vitamin D and Breast Cancer—The Real Story

The general view of vitamin D is that it is important for reducing the incidence of breast cancer. This is the view presented in a recent interview with Karen Marrs of the Cancer Treatment Centers of America. This is the link to the complete article and video: Vitamin D Deficiency Could Put Women at Risk for Breast Cancer.


Unfortunately, research supporting this view is uneven. An overview of research on vitamin D and breast cancer, presented by the Susan G. Komen Foundation states that, “Findings from studies on vitamin D (through diet alone or diet plus sunlight exposure) and breast cancer risk are mixed.”

The Cancer Treatment Centers of America and the Susan G. Komen Foundation both miss a crucial point. That point is that the vitamin D deficiency associated with breast cancer is a deficiency in vitamin D3 sulfate.

A vitamin D3 sulfate deficiency means a deficiency of sunshine on your skin.

How does your skin make vitamin D? The process requires three basic ingredients:

  • Sunshine in the ultraviolet range, specifically UVB
  • Sulfur
  • Cholesterol

The process begins when UVB light hits your skin. The energy from UVB light causes sulfate to be joined to cholesterol in your skin. Cholesterol sulfate is then converted to vitamin D3 sulfate.

Fortunately, sulfur is a plentiful substance in your diet, you make plenty of cholesterol in your skin, and UVB light is a free resource from sunshine.

The process of making vitamin D3 sulfate is jeopardized if you take cholesterol-lowering drugs. Indeed, taking statins is associated with an alarming increase in breast cancer incidence (2008).

Women also undermine the process by not getting enough sunshine on their skin. In the extreme, those who get the least amount of UVB light on their skin have the lowest amounts of circulating vitamin D and the highest incidence of breast cancer (2012).

In contrast, women who live in the lowest latitudes, closest to the equator, have the highest levels of circulating vitamin D and the lowest incidences of breast cancer (2014), especially in summertime when UVB rays are at their most potent.

The real story behind the benefits of vitamin D and breast cancer is, therefore, a story about vitamin D3 sulfate, cholesterol, sulfur, and sunshine. Neither dietary nor supplemental vitamin D is part of that story.

Ultimately, your own native vitamin D—vitamin D3 sulfate—is the key to reducing your risk of breast cancer.