Those who know me know I've been managing type 2 diabetes for a while now. By the numbers that are supposed to matter, things are good — I've lost real weight, and my last A1C came back at 6.0%, solidly in well-controlled territory. By every metric my doctor tracks, I was doing this right.
So when the fatigue didn't lift, I figured it was just diabetes being diabetes. Fatigue is a real, well-documented part of living with this disease — that part isn't in my head, and it isn't solved just by getting your numbers down. I also have ringing in my ears that's been there for about 2 years now. And my hands go ice-cold any time it dips below about 72°F indoors — genuinely freezing, not just chilly. Then, on the other end, Texas summers have gotten flat-out devastating in a way they never used to be. I've got a small yard, nothing crazy, but when it's already 95°F at 8 in the morning, I can't get through yard work in one go anymore the way I used to. I figured it was all just what a body does as it gets older.
Then a lab panel showed a ferritin of 6 ng/mL.
Starting ferritin: 6 ng/mL (critically low) · A1C at the time: 6.0% (well-controlled) · Expected recovery: 8–12 weeks with repletion
The Symptoms I'd Been Writing Off
The fatigue made sense to write off — diabetes fatigue is real, regardless of how good your control looks on paper. But the rest of it lined up with iron deficiency more specifically than I realized at the time. Cold intolerance is one of the classic, well-recognized signs of iron-deficiency anemia — your body needs adequate iron to regulate temperature efficiently, and when it's running short, freezing indoors at temperatures nobody else even notices isn't unusual.
The tinnitus surprised me more. A meta-analysis covering four studies and more than 344,000 adults found the odds of hearing loss were 55% higher in people with iron-deficiency anemia than in people without it, and separate research has found that the reduced oxygen delivery from iron deficiency can affect the tiny hair cells in the cochlea that convert sound into nerve signals, which may cause or worsen the perception of ringing or buzzing. It's not a universal symptom — plenty of people with low iron never get it — but two years of unexplained ringing suddenly had a candidate explanation I'd never once considered.
The heat intolerance is the one piece I can't tie to iron specifically with the same confidence — that one might be something else entirely, still worth a separate conversation with my doctor rather than a tidy explanation.
Why None of This Raised a Flag Sooner
Here's the part that actually got me: every symptom on that list had an easy, ready-made explanation already sitting in front of me. Tired? Diabetes does that. Ringing ears, can't handle the temperature swings? Just getting older. None of it pushed me to ask, "Could this be something else?" because I already had an explanation that fit well enough not to question.
It turns out there's a documented reason GLP-1 medications specifically make this kind of thing easy to miss. A 2026 review published in the journal Clinical Obesity, pooling six studies and nearly half a million adults on GLP-1 medications like semaglutide and tirzepatide, found vitamin D deficiency in 7.5% of users at six months and 13.6% by twelve months, with iron deficiency showing up right alongside it. A separate registry study found that GLP-1 users had ferritin levels 26-30% lower than those on other diabetes medications. The mechanism is straightforward: these drugs suppress appetite and slow digestion — that's literally why they work — which also means less food intake and, specifically for iron, reduced absorption.
Why I Finally Got Tested At All
None of this got caught because my doctor happened to think of it on his own. My complaints — the fatigue, the ringing, the temperature swings — had been sitting on the table for over a year before anything beyond the basics got checked. What actually moved things was insisting on a thyroid panel specifically, because thyroid disease runs in my family, and that gave me something concrete to ask for instead of a vague "something feels off." That specific, named request opened the door to a broader round of bloodwork, and my doctor used the same draw to check iron and cortisol. The iron is what caught the ferritin of 6.
The cortisol raised its own open question, one I'm still working through with my doctor right now — not something I'm ready to write about yet, but I will once there's a real resolution instead of just more questions. That's a piece for another day.
If I'd kept describing symptoms in general terms instead of naming an actual test and a specific reason to run it, I genuinely don't know how much longer any of this would have gone unchecked. Don't just tell your doctor you're tired. Ask for the test by name.
What I'm Actually Doing About It
My doctor put me on iron bisglycinate paired with vitamin C, taken together on an empty stomach. Iron bisglycinate specifically because it's gentler on the stomach than older iron forms, and vitamin C because it measurably improves how much of it your body actually absorbs. The timing rules matter more than I expected: no coffee 30 minutes beforehand, nothing with calcium within two hours, no cola. Get the timing wrong, and you're not really getting the iron anyway.
I'm also dealing with a vitamin D deficiency — though unlike the iron, this one isn't new. It's been there since my original diabetes diagnosis, long before Mounjaro ever entered the picture, and it's stubborn. I've been taking 5,000 IU a day for years now — well above what most doctors typically recommend as a standard dose — and my levels still only come back middle-of-the-road, never genuinely low anymore, but never optimal either. This is the one place I'll actually push back on how most people approach it. I take D3 paired with K2, not D3 alone, and I'd recommend anyone fixing a vitamin D deficiency do the same rather than grab a plain D3 bottle off the shelf. Here's why: Vitamin D's job is to increase how much calcium your gut pulls in from food. That's it — it has no say over where that calcium actually goes afterward. That routing job belongs to K2, which activates a protein called matrix Gla protein, the thing that actually directs calcium into your bones and teeth and keeps it out of your arteries and soft tissue. Correct a real deficiency with D3 alone, at a dose strong enough to matter, and you're increasing the calcium circulating in your blood without giving your body the tool it needs to send that calcium somewhere useful instead of somewhere it can cause problems down the line. The two are meant to be taken together, not as a choice between one or the other.
One more thing I've noticed since starting the combination, though I don't have a confirmed explanation for it: the plaque buildup between dental cleanings has noticeably dropped off. I can't tell you with certainty that's the K2 routing calcium more efficiently rather than something else changing at the same time — I'm not going to pretend I have that nailed down. But it's a real change I've noticed, worth mentioning rather than leaving out, even without a tidy explanation to go with it.
One More Thing Worth Checking: B12, Especially If You're on Metformin
If you're a diabetic reading this and you're on Metformin — or have been, like I was before switching off it — there's a second, separate nutrient gap worth knowing about, one that's actually been documented in medical research since the early 1970s, far longer than anything about GLP-1 drugs. Metformin interferes with how your gut absorbs vitamin B12, and the risk climbs with both higher doses and longer time on the medication. Deficiency rates in long-term Metformin users have run as high as 28 to 30 percent in some studies — this isn't a rare side effect, it's a genuinely common one that often goes unchecked for years.
Here's the part that surprised me most, digging into this: a plain multivitamin might not actually fix it. One study found that a standard multivitamin containing the typical 6 mcg of B12 made no measurable difference in deficiency rates among Metformin users, while a B-complex supplement with more than 200 mcg did. Dose matters here specifically, not just "are you taking something." I've started on a methylated multivitamin for exactly this reason, rather than assuming any multivitamin would do the job.
It's also worth noting that B12 deficiency can present as tingling, weakness, balance problems, or brain fog — without ever showing up as anemia on a standard blood count. That means a normal CBC doesn't rule it out. If you're on Metformin, past or present, and any of those symptoms sound familiar, the fix isn't a better multivitamin guess — it's asking for an actual B12 level on your next lab draw.
Everything linked at the bottom of this piece is exactly what's sitting in my own cabinet right now — not a generic "here's a popular brand" recommendation. Naked Iron Bisglycinate because it's the gentler-on-the-stomach form my doctor specifically pointed me to. Solaray Liposomal Vitamin C, because that's what I actually pair it with for absorption, per doctor's orders. UpNourish D3+K2 because it's the real combination product I take, not two separate bottles I'm juggling. Pure Therapro Rx Methylated Multivitamin, because it's methylated specifically, not a standard drugstore multivitamin with the lower-dose B12, the research above says, isn't enough.
Call to Action: If You're on a GLP-1 Medication, Ask for These — By Name
- A full iron panel, including ferritin specifically — not just a basic CBC, which can look normal even when iron stores are genuinely low.
- Vitamin D levels — the single most commonly flagged deficiency in the GLP-1 research. If you're correcting it, ask specifically about D3 paired with K2, not D3 alone.
- A B12 level specifically, especially if you're on Metformin now or have been in the past — a normal CBC does not rule this out, and a standard multivitamin's dose may not be enough to fix it once it's low.
- Thiamine — flagged in multiple studies, and thiamine deficiency in particular, can get serious if it goes unnoticed.
- If your doctor isn't picking up on something, find one specific, named test tied to a real reason — family history, a documented symptom, anything concrete — and ask for it directly. A vague "I'm tired" is easy to dismiss. A specific named request usually isn't.
This isn't a reason to stop a medication that's working for you — it's a reason to ask for the bloodwork before fatigue, or worse, gets written off as "just diabetes" or "just the GLP-1."
This is one person's experience, not medical advice. Talk to your own doctor before starting any supplement, especially alongside prescription medication.