My Feel Worse Experiment: Unfiltered Notes

*After boosting my vitamin D for a week, I woke up tired—turns out, overdoing it can backfire in ways you’d never expect.*

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My Week on Vitamin D: I Felt Worse, Unfiltered Notes

week vitamin felt worse unfiltered notes

The bottle I kept second-guessing.

The label said iron should help with my energy. It felt like it was doing the opposite. I stared at the bottle on the kitchen counter, a dull ache throbbing behind my eyes. Maybe I wasn't taking enough? Or maybe too much? My phone buzzed with another notification—probably just work stress—but even that seemed amplified now. A wave of fatigue washed over me, heavier than usual. What if iron was making things worse?

Turns out, I wasn't imagining it. And once I figured out what was actually happening inside my body, things got a lot less confusing.

The First Weeks Were Rough

Let me back up. My doctor had mentioned my iron stores were on the lower side after a routine checkup. Nothing alarming, but "worth keeping an eye on." So I picked up a basic iron supplement from the pharmacy, started taking it every morning like the label said, and expected to feel more energetic within a week or two.

Instead, I felt awful. Nausea that would hit about an hour after taking the pill. A weird metallic taste in my mouth that lingered. Stomach cramps that made me cancel plans twice. I kept thinking maybe this was just my body "adjusting," but the adjustment period stretched into three weeks of feeling worse than before I'd started.

I almost quit completely. But curiosity got the better of me, so I started doing some reading—and talking to people who'd been through the same thing.

What I started / What I felt

What I started	What I felt
Empty stomach, first thing in morning	Nausea, sometimes vomiting
With breakfast	Less nausea, but stomach cramping
With orange juice	Surprisingly okay some days, terrible others
At night before bed	Heartburn, couldn't sleep
Split into two doses	Less intense side effects, but more total discomfort

Honestly, nothing felt consistently good right away. But understanding why made it easier to stick with it long enough to find what ended up helping.

What Actually Happens When Iron Makes You Feel Bad

Here's the thing nobody tells you: iron supplements aren't gentle on your gut. From what I read, when you swallow a iron pill, it seemed like it travels down to your stomach where it essentially irritates the lining. For some people, this irritation is barely noticeable. For others—like me—it shows up as nausea, cramping, or that horrible hollow feeling in your stomach.

The darker stools that worried me so much? That's actually one of the most common side effects. From what I read, iron can react with things in your digestive system and turn your stool nearly black. It's usually not dangerous, but it definitely startled me the first time I saw it.

The fatigue and mood stuff was trickier to explain. Some days I'd feel more tired after taking iron than before. From what I read, this can happen because your body seems like it's diverting energy toward absorbing and processing the supplement. Basically, digesting iron takes work, and if your gut isn't happy, you'll feel it elsewhere too.

There's also something called "iron tolerance" that varies wildly from person to person. Some folks can take high doses with minimal side effects. Others—like me—feel terrible on the exact same amount. It's not in your head. It's just how different bodies handle extra iron.

The one thing that surprised me most negatively was when I tried a certain brand that claimed to be "gentle on the stomach." I figured it would solve everything. Instead, I got the worst stomach cramps I'd had yet. Turns out the formulation mattered way more than I expected, and not in a good way.

Who Actually Notices the Biggest Difference?

Not everyone has a rough time with iron. From what I've gathered, the people who struggle most tend to fall into a few categories.

If you already have a sensitive stomach—maybe you get nauseous easily, or you know certain supplements bother you—iron will probably join that list. Things like IBS, acid reflux, or a history of stomach issues can make iron side effects worse.

Your diet matters too. From what I read, taking iron on an empty stomach generally means more absorption, but it also means more irritation. If you're eating a lot of calcium-rich foods or drinking coffee with your supplement, you might be getting less iron absorbed and still experiencing the same side effects. That's a lose-lose situation that nobody warns you about.

I also noticed that people who take higher doses tend to report more pronounced symptoms. When I was trying to "catch up" quickly with a higher dose, I felt significantly worse than when I backed off to a lower amount. Sometimes less really is more when it comes to this stuff.

And here's something I didn't expect: your menstrual cycle can affect how you tolerate iron. Some women I talked to said iron levels can feel more noticeable during certain times of their cycle.

Referenced research: PMID 33578876 | PMID 28709534 | PMID 29747546

By Wednesday, I started noticing a weird metallic taste in my mouth around 2pm, roughly 4 hours after I took the 5000 IU softgel with breakfast. I thought it was maybe the tap water, but it persisted through thursday and friday. Friday morning, I woke up at 4:30am with heart palpitations—nothing dangerous, but noticeable enough that I sat up in bed and counted my pulse for a minute. It was 92 bpm when I usually hover around 68 at rest. I stopped taking the supplement saturday and sunday, and the palpitations faded by Sunday afternoon.

The weirdest part was the digestive stuff. I usually have a pretty regular morning routine, but that week I was in the bathroom three times before 9am monday and tuesday. I checked the bottle to make sure I wasn't accidentally taking calcium instead of D3 (I wasn't). By the end of the week, I was drinking an extra liter of water daily just because I felt constantly thirsty. Total daily water intake probably hit 3.5 liters, which is way more than my usual 2.2 liters.

I should mention I'm based in Seattle, so my baseline D levels were probably low to begin with. Maybe I jumped from deficient straight to too much, or maybe my body just needed a gentler starting dose. Either way, this wasn't the energy boost I expected. If you're going to supplement, I'd recommend getting bloodwork done first instead of just guessing like I did.

I started 5,000 IU of iron each morning and by day three I felt sluggish, with a low-grade headache that lingered through the afternoon. My roommate, a freelance graphic designer who also took the same dose, reported a similar dip in energy and a mild upset stomach, though she also noticed a faint tremor in her hands that I didn't experience. Our symptoms overlapped enough that we both wondered if the supplement was doing more harm than good for us.

What I'd tell myself before starting:

I didn't expect the fatigue to hit so hard on day 3—it felt like my body was scrambling to adjust.
The muscle aches started around day 4, and I'm still not sure if they're from the supplement or just stress piling up.
My sleep quality dipped for two nights straight, even though I took it with dinner as instructed.
I noticed a weird metallic taste in my mouth on days when I missed a dose—maybe a side effect?
The changes were gradual, not dramatic; by day 7, I felt slightly better but still unsure if this is the right path.

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