Your Vitamin D Number Is Lying to You

The Number That Should Stop You in Your Tracks

Studies show that between 70% and 96% of women are vitamin D deficient at the time of their breast cancer diagnosis.

Let that sink in.

Not a small number. Not an outlier finding. Seventy to ninety-six percent. And here's what makes that number even more troubling: those studies define deficiency as a level below 20 or 30 ng/mL. That's the bar. That's what medicine decided counts as a problem worth noting.

But a vitamin D level of 30 is not optimal. It is simply not a failure by the most minimal definition we've set for ourselves. We have built a medical system that is satisfied with avoiding catastrophe rather than pursuing health — and nowhere is that more apparent than in how we think about vitamin D.

Most women who are diagnosed with breast cancer were already depleted. And that depletion didn't just coincide with their cancer — it helped create the conditions for it.

Vitamin D deficiency sets the stage for breast cancer.

Which means this isn't a conversation we should be having after a diagnosis. It's a conversation we should be having years before one — so that we never have to have it at all.

And here's where it gets worse: even the test we use to measure vitamin D isn't telling the whole story. The number your doctor hands you — the one they call normal — may be masking a deficiency your body is desperately trying to compensate for. Right now. Without you knowing.

This blog is about changing that.

Whether you are trying to prevent a breast cancer diagnosis, navigating life after one, or living with metastatic disease, this is information you need. Not your doctor's version of acceptable. Not the bare minimum. The full picture.

This, my friends, is what you need to know about your vitamin D.

Vitamin D Is Not a Vitamin

Despite its name, vitamin D is not really a vitamin. It is a hormone. And that distinction matters more than most people realize.

Vitamins are things your body cannot make on its own — you have to get them from food. Vitamin D is different. Your body is designed to produce it. It has receptors for it in virtually every tissue and organ. It uses it to regulate processes happening all over your body, all day long. That is not what a vitamin does. That is what a hormone does.

And when a hormone is missing — when a critical messenger your body depends on simply isn't there — things start to go wrong. Quietly at first. Then not so quietly.

Here is what vitamin D does:

It is one of the most powerful regulators of your immune system, helping it identify real threats, mount a real defense, and stand down when the threat is gone. An immune system without adequate vitamin D is an immune system flying blind.

It controls inflammation. And chronic, unrelenting inflammation is not just uncomfortable — it is the environment in which cancer grows.

It regulates cell growth. It tells cells when to grow, when to stop, and when to die when their time is up. That last part — programmed cell death, called apoptosis — is one of your body's most important cancer defenses. Vitamin D is a key part of that system.

It supports bone strength, heart health, brain function, and mood.

And it plays a direct role in suppressing cancer cell activity — including breast cancer cells specifically.

This is not a vitamin you take to avoid a deficiency on a lab report. This is a hormone your body needs to function, to protect itself, and to heal. The difference between having enough and not having enough is not a technicality. It is the difference between a body that can defend itself and one that cannot.

How Your Body Makes Vitamin D

Here is something remarkable that we have somehow forgotten: your body was designed to make vitamin D. Not to hunt for it in food, not to rely on a supplement bottle — to make it, from sunlight, in your own skin.

When ultraviolet B rays from the sun reach your bare skin, they trigger a conversion process. A compound in your skin called 7-dehydrocholesterol absorbs that UVB energy and is converted into an early form of vitamin D. That early form then travels to your liver, where it is converted again into 25-hydroxyvitamin D — the form we measure in a blood test. From there, it travels to your kidneys, where it is converted one final time into the fully active form your body actually uses.

Three steps. Sun to skin. Skin to liver. Liver to kidneys. And at the end of that process, your body has the active hormone it needs to control inflammation, protect your cells, and defend itself against the kind of cellular chaos that leads to cancer.

This system is elegant. It is ancient. It evolved over hundreds of thousands of years of human beings living, working, and moving in sunlight.

And in the span of a few decades, we have dismantled it almost entirely.

We Vilified the Sun

We vilified the sun for the purposes of creating fear and selling unimaginable amounts of sunscreen.

The story we were told was that skin cancer was an epidemic and the sun was the cause. It was a tidy narrative. It was also enormously profitable. Sunscreen became a multi-billion dollar industry almost overnight and with it came something far more costly than the price of a bottle of SPF 50. It came with a vitamin D deficient society. One that would become increasingly sick. Increasingly reliant on a medical system with an endless supply of solutions to sell.

I do not think this was an accident.

We were intentionally undereducated about vitamin D. What it is, what it does, and what happens when we don't have enough of it. That undereducation extended to our doctors and providers. Most practitioners today could not tell you the difference between a vitamin D level that is simply not a failure and one that is actually optimal. Because nobody taught them. Because there was no profit in teaching them.

The sun is the source of life. It is healing. It is regenerative. It is the way your body was designed, for hundreds of thousands of years, to produce the hormone it needs to regulate your immune system, protect your cells, and defend you against the kind of cellular breakdown that leads to cancer.

We blocked that process. And we have the disease rates to show for it.

And yes, go ahead and throw away your sunscreen. I mean that. The honest truth is that for most of us, it doesn't matter anyway. Most of us live in climates where optimal UVB exposure is only available a few months of the year, if that. We work indoors. We dress for cold weather. We live at latitudes where the sun's angle through most of the year means UVB rays barely reach us regardless of what we put on our skin.

Most of us cannot get what we need from sunlight alone anymore. Not because of sunscreen because of how we live.

Which means most of us, without intentional supplementation, are vitamin D deficient. And the consequences of that deficiency are far greater than any of us have been told.

Now here is what you actually need to understand. Vitamin D's single most important job in your body isn't your bone health, or even your immune system it's regulating calcium. And calcium regulation is not a small thing it is a system so critical that your body will go to extraordinary lengths to protect it. Understanding that system is the key to understanding why a vitamin D blood test alone is not enough and what you need to ask for instead.

The Real Story

When your doctor orders a vitamin D test, they are measuring a form called 25-hydroxyvitamin D, sometimes written as 25(OH)D. This is the storage form. Think of it as vitamin D sitting in a warehouse, waiting to be activated and put to work. It tells you how much you have on hand. It does not tell you what your body is doing with it.

And that distinction is everything.

In my practice, I aim for a vitamin D level of 60 to 100 ng/mL. Most conventional labs call anything above 30 normal. As we have already established, normal is not optimal. Normal is simply not a failure. And for something this important, for a hormone this central to your body's ability to protect itself, not a failure is not good enough.

And here is something else that medicine rarely tells you: vitamin D adequacy is not the same for everyone. Some people require significantly higher levels to achieve the same protective effect. There is real and meaningful variation from person to person based on genetics, body weight, age, and how well your body converts and activates vitamin D. And it is not even constant within the same person. When your body is under stress, when you are sick, when you are healing, when you are facing a cancer diagnosis, your demand for vitamin D increases. You need more of it precisely when you are most depleted and most vulnerable.

But here is what I really need you to understand. Even if your vitamin D level looks perfect on paper, that number alone cannot tell you whether your body is actually doing what it needs to do with it. Because vitamin D's most critical job, the job that everything else depends on, is regulating calcium.

Calcium is not just about strong bones. The calcium circulating in your blood is doing life-sustaining work every single moment of every single day. It keeps your heart beating. It keeps your muscles contracting. It keeps your nerves firing. It keeps your cells communicating. Your body protects blood calcium levels with extraordinary vigilance — because even the slightest drop is a crisis.

And the way your body maintains that calcium balance — the mechanism it relies on — is where the real story of vitamin D lives.

The Alarm System

Inside your neck, tucked behind your thyroid gland, are four tiny glands called the parathyroid glands. Most people have never heard of them. Most people will never think about them. But these four small glands are running one of the most critical safety systems in your entire body — and they have everything to do with whether your vitamin D is actually working.

Here is how the system works.

When vitamin D is doing its job, your intestines absorb calcium efficiently from the food you eat. Blood calcium stays stable. The parathyroid glands stay quiet. Everything runs smoothly.

But when vitamin D is insufficient — even when your blood level looks acceptable on a lab report — calcium absorption starts to slip. Blood calcium begins to fall. And the parathyroid glands respond immediately. They release a hormone called parathyroid hormone, or PTH. And PTH is your body's calcium rescue signal.

Once PTH is released, it goes to work:

• It pulls calcium out of your bones to restore blood levels

• It tells your kidneys to stop losing calcium in urine

• It pushes your body to activate whatever vitamin D it can find in an attempt to absorb more calcium from food

Your body will do all of that, will literally pull calcium from your bones, before it will allow blood calcium to fall. That is how non-negotiable calcium regulation is.

PTH is the alarm. And when that alarm is ringing, it means one thing: your body does not have enough effective vitamin D to maintain calcium balance on its own.

This is why PTH is a far more meaningful measure of vitamin D adequacy than vitamin D alone. Your vitamin D level tells you what is in the warehouse. PTH tells you whether the warehouse is actually meeting the demand.

You can have a vitamin D level of 60 — seemingly adequate — and a PTH that is elevated, meaning your parathyroid glands are working overtime to maintain calcium balance. That is not optimization. That is compensation. And compensation is not the same as thriving.

Two women. Same vitamin D level of 60 ng/mL. By every standard lab reference range, they both look fine. But when we check PTH:

Woman A has a PTH of 75. Her parathyroid glands are sounding the alarm. Her body is pulling calcium from bone. Her vitamin D, despite the number, is not adequate for her needs. Woman B has a PTH of 21. Her calcium regulation is effortless. Her vitamin D is doing exactly what it should.

Same number. Completely different reality.

This is what a single vitamin D test cannot show you. And this is why I do not stop there.

Why Supplementing Isn't Always Simple

So you've had your vitamin D checked. It's low. Your doctor hands you a bottle of vitamin D3 and sends you on your way. Problem solved, right?

Not quite.

D3 is a precursor. It is the raw material, not the finished product. Before your body can actually use it, D3 has to be converted — first in your liver, then in your kidneys — into the fully active form called calcitriol. That is the form your cells actually respond to. That is the form that regulates calcium, modulates your immune system, and does everything we have been talking about.

That conversion process can be sluggish. Age slows it. Inflammation slows it. Impaired kidney function slows it. Certain genetic variations slow it. A woman can be taking D3 faithfully every single day, watch her vitamin D level climb on paper, and still have a body that is not activating it properly. The warehouse is full. The shelves in the store are still empty.

This is why, for patients who are in active cancer treatment or recovery — women who are in crisis and do not have months to slowly build stores — I often use calcitriol directly. It bypasses the conversion process entirely and delivers what the body needs immediately. [Note: Calcitriol is a prescription medication and requires careful clinical supervision.]

And then there are the cofactors. Vitamin D does not work alone.

Magnesium is essential for the conversion of vitamin D into its active form. Without adequate magnesium, the entire process stalls — and most people are already magnesium deficient.

Vitamin K2 works in partnership with vitamin D to direct calcium where it belongs — into bones and teeth — and away from where it causes harm, including arterial walls and soft tissues. Supplementing vitamin D without K2 can, over time, send calcium to exactly the wrong places.

A bottle of D3 is a starting point. It is not a protocol.

The New Standard We Need

There was a time when we did not measure vitamin D at all. That is changing. And that is progress. But it is not nearly enough.

It is time to retire the idea that a single vitamin D number tells you what you need to know. It does not. The science has moved. The tools are available. The understanding exists. What has not caught up is the standard of care.

I want to change that. Starting with you.

If you take nothing else from this, take this: vitamin D cannot be evaluated in isolation. To truly understand whether your body has what it needs, whether your calcium regulation system is running smoothly, whether your cells are getting the protection they deserve, you need three numbers, not one.

Vitamin D.

PTH.

Calcium.

Together, these three tell a story that no single number can. Your vitamin D level tells you what is in storage. Your PTH tells you whether your body is struggling to maintain calcium balance despite that storage. And your calcium level completes the picture, helping your provider distinguish between vitamin D insufficiency and other reasons PTH might be elevated.

These are not exotic tests. They are not expensive. They are not complicated to order. They are simply not being ordered because most providers were never taught to look at them together, and because a system focused on treating disease has very little incentive to optimize health.

That has to change.

Vitamin D optimization is not a luxury. It is not a wellness trend. It is not something to think about after a diagnosis forces the conversation. It is foundational. It is the kind of thing that, done right, done early, done consistently, may mean you never need to have certain conversations at all.

You deserve a provider who understands this. Who looks at the full picture. Who is not satisfied with a number that simply clears the lowest possible bar and calls it normal.

And if you do not have that health partner yet you do now.

Schedule a call with us here and let us help you on your breast cancer prevention or recovery journey.

With Gratitude,

Dr. Jenn

Note: This article is for informational purposes only and does not constitute medical advice. Patients should consult with their healthcare providers before making any decisions regarding hormone therapy.