Heavy Legs on Easy Runs? 5 Reasons Your Ferritin Is Stuck (Reason 3 Is the Dose You Already Upped)

Told your ferritin was “normal”? On October 5, LabCorp moved the line from 15 to 30.

Until October 5, 2026, LabCorp’s range for women started at 15. A 17 came back in range, with no flag at all.

Now the range starts at 30. The same 17 comes back low.

It also depends on the lab. When we checked on October 7, 2026, Quest’s range for women in its East region still started at 16. So the same 17 can read normal at one lab and low at the other.

The American Society of Hematology’s 2026 guideline diagnoses iron deficiency at a ferritin of 30 or lower. That means a 17 counts as iron deficiency, even on a report that printed “normal.” With heavy periods or symptoms of low iron, the guideline says a line of 50 is appropriate.

Your target number is your doctor’s call, not ours. So ask for ferritin by name, and read the number yourself. In most states you can order the test online, with no doctor’s visit.

One buyer told us what happened when they finally asked:

That’s why your number can read low. Reasons 2 to 5 are why it stays there.

Run and have periods? You’re in both groups that a 2019 review singles out for low iron.

A 2019 review of athlete research reports iron deficiency in about 15% to 35% of female athletes, depending on the group studied. It singles out women and endurance athletes.

Periods cost iron every month. In a Swedish study of 476 women, the 1 in 10 with the heaviest periods lost 1.35 mg of iron a day or more. That’s nearly three times what the typical woman lost.

So you can eat well, train smart and still run low.

One runner wrote this under our ad, right after buying:

If you already upped your dose to make up for it, Reason 3 is for you.

You didn’t fail iron. The dose did.

When a number won’t move, the usual advice is to take more. Two very different trials put “more” to the test: one in hospital patients over 80, one in blood donors. Both got the same answer.

The first gave patients 15, 50 or 150 mg of iron a day for 60 days. Hemoglobin, a number on your blood count, rose about the same on all three: 1.3 points on 15 mg, 1.4 on 150.

The big dose cost more. 70% on 150 mg had stomach discomfort, against 20% on 15 mg. And 27% dropped out on the big dose, against 7% on the small one.

The second trial, called STRIDE, ran for two years. After each blood donation, donors took 19 mg of iron a day for 60 days, or 38 mg, or a pill with no iron. Nobody knew which one they had.

Two years in, while still giving blood, the 19 mg group and the 38 mg group had rebuilt about the same amount of iron.

Many iron-only supplements have 65 mg. That’s 360% of the Daily Value. Our strip has 19 mg, the same daily amount as STRIDE’s lower dose.

So if you upped your dose and nothing moved, a bigger dose may not be the fix. Two other things may be in the way: a pill your stomach fights, and what you take it with.

The first one is sitting in your pill bottle.

Check your pill bottle. If ferrous sulfate upsets your stomach, there’s iron with no pill to swallow.

Ferrous sulfate is the standard iron pill. If your bottle says 325 mg of ferrous sulfate, that’s 65 mg of iron a pill. In 20 trials against a pill with nothing in it, ferrous sulfate carried about 2.3 times the odds of stomach and gut side effects. All but one of those trials were in healthy people without anemia.

About 7 in 10 of the buyers we asked had tried iron pills before ours. One Reddit commenter put it like this:

A pill you stop taking can’t raise your number, and quitting one that hurts isn’t a willpower problem. So we sell iron as a strip instead.

It’s called cavaé melt: a thin raspberry strip with 19 mg of iron. Tear open the sachet, set the strip on your tongue and let it melt. Then swallow. No pill. No water.

• Iron: 19 mg as ferric saccharate, 106% of the Daily Value. No ferrous sulfate.
• Folate: 400 mcg DFE, from 240 mcg of folic acid.
• Taste: raspberry, sweetened with monk fruit and stevia.
• A tin: 30 strips. One a day.

Two people who took it:

Your stomach gets the final say. If it says no, that’s what the 60-day guarantee is for.

One tin $59.99 · Three tins $44.99 each · 60-day money-back guarantee

After Reason 5: three people’s ferritin, before and after the strip. One didn’t move.

Iron with your morning coffee? Move one of them.

The same goes for tea, calcium and some medications. Leave a gap when you can.

You can take the strip any time of day, so pick a time away from your coffee.

Take levothyroxine (Synthroid) for your thyroid? Its label says not to take it within 4 hours of iron. For other prescriptions, ask your pharmacist about timing.

That’s all 5. Next, how to test the fix on your own blood work, inside 60 days.

Test the strip on your own blood work. 60 days, or your money back.

When to test: while your order ships if you can, then around week six for a first look. If your first test says you don’t need iron, the 60 days cover that too.

This commenter went from 25 to 45 by day 30:

This one moved from 6 to 14:

And this one saw no change:

All three are self-reported, not checked by us against a lab report.

Not every number moves. If yours doesn’t, our 60-day money-back guarantee covers you.

Two ways this can go.