Stiff, Sore, and Low on D

The CEO Never Stops Working

I wrote a post a few weeks ago about being the CEO of your cancer journey — organizing your records, knowing your case, showing up to every appointment already briefed. That post was about building the foundation.

This one is about what happens when you actually use it.

The Gap in the Records

Once my medical files were consolidated — labs, imaging, pathology, chemo history — I could see the whole picture for the first time. That's the value of the work. Not just having the records, but being able to read them like a ledger.

Two line items stood out: Vitamin D and cholesterol. Neither had been checked in years. Not flagged, not ordered, just quietly missing from the record.

I requested both.

I already suspected the Vitamin D before the blood draw. I'd bought a supply of supplements while I was in the States — a hedge. When the result came back at 15.7 ng/mL, the flag read insufficient. My level had dropped from 31.2 ng/mL in 2020.

I wasn't surprised. But I wanted to understand why it mattered beyond the flag.

The Body Aches — Where This Started

Chemo has been making my muscles feel stiff and painful. Not dramatically — no single symptom that sends you to the ER — but a persistent, annoying kind of stiffness. Tight shoulders, neck, and lower back. The kind of aching that makes you walk like C-3PO — stiff and jerky.

Chemo can create muscle stiffness through several overlapping mechanisms at once:
— Systemic inflammation from treatment
— Deconditioning — you move less, muscles stiffen, movement hurts more, repeat
— Neuropathy altering how you move without you realizing it
— Electrolyte shifts from FOLFIRI and diarrhea
— Low iron availability reducing recovery capacity

My CRP has been persistently elevated during FOLFIRI — ranging 2.20 to 3.10 mg/L. That confirms a low-grade inflammatory state. Not alarming, but enough to make joints and muscles feel heavy and slow to loosen.

And then there's iron — which deserves its own explanation.

The Iron Problem — It's Not Anemia, But It's Not Nothing

My transferrin saturation came back at 18% — flagged low. My hemoglobin was 14.4 g/dL, which is normal. No clinical anemia. So what's the problem?

This is called functional iron deficiency. The iron exists in storage, but the body can't move it efficiently into circulation. Transferrin saturation below 20% is the threshold most hematologists use to flag impaired iron availability. At 18%, I'm just under it.

The likely cause: FOLFIRI and ongoing inflammation. When CRP is elevated — mine has been consistently above 2.0 throughout treatment — the body actively sequesters iron as part of the inflammatory response. It's a defense mechanism. It's also the reason you can have adequate iron stores and still feel like you're running on empty. Fatigue amplified. Muscle recovery slowed. Everything just a little harder than it should be.

I've been here before. In late 2024, before any cancer diagnosis, a routine thyroid checkup turned up dangerously low iron — two IV infusions followed. In hindsight, this was the first sign that I had colorectal cancer.

The fix isn't simply eating more red meat, though heme iron from animal sources absorbs significantly better than plant-based iron. The real question, given active chemotherapy and elevated inflammation, is whether oral supplementation can even move the needle. Gut absorption is suppressed when CRP is elevated. You can take the pills and the number may not budge.

The more direct solution is IV iron — it bypasses the gut entirely and raises transferrin saturation faster and more reliably. That's the conversation to have with the oncologist: at what threshold do we stop watching and start treating? I'm asking that question at the next appointment.

In the meantime, the dietary levers are heme iron — red meat, organ meat — paired with Vitamin C to improve absorption of non-heme sources. Not a correction. A contribution.

Why Vitamin D Matters for Muscles

At 15.7 ng/mL, I'm in the insufficient range. Vitamin D deficiency can cause muscle aches, weakness, cramps, bone and joint pain, and fatigue. It's not a dramatic presentation — it just makes everything feel worse, which is exactly what I was describing.

The fix seemed straightforward. I had D3 softgels I'd bought in the States — 2,000 IU per capsule. I asked my oncologist about the dosage.

Two Forms of Vitamin D — Not the Same Thing

This is where it got interesting, and worth understanding if you're managing your own supplementation.

My oncologist prescribed calcifediol 0.266 mg — not the standard over-the-counter Vitamin D3.

Here's the difference:

Vitamin D3 / cholecalciferol — the common supplement form. Your body converts it first in the liver, then again in the kidneys. It works, but it's slower and more variable.

Calcifediol / 25-hydroxyvitamin D — the already liver-converted form. It raises blood levels faster, more predictably, and without depending on how well your liver handles the conversion step. That matters more when you're sick, dealing with inflammation, or otherwise not operating at baseline absorption.

The prescribed protocol: one capsule every 15 days for one month, then one capsule monthly. In Portugal, this is sold as Hidroferol.

The important note: the two forms are not interchangeable. Different molecule, different potency, different dosing rhythm. My 2,000 IU D3 softgels are a daily maintenance supplement. The calcifediol is a targeted correction. Using one in place of the other would be a mistake — and not a small one.

Getting your records organized doesn't just help with the big decisions — the surgery consultations, the insurance reviews, the second opinions. It also catches the quiet gaps. The labs that haven't been ordered. The deficiencies that have been building unnoticed while everyone's focused on the primary diagnosis.

The body aches are real. The causes are layered and overlapping. And most of them have something you can actually do about them — if you know how to look.