Iron & ferritin: fatigue's most-missed cause

Ferritin before hemoglobin

Standard "anemia" screening looks at hemoglobin — but hemoglobin is the last thing to fall. Your body defends it by draining stored iron first, and ferritin is the gauge on that store. That's why you can be told "you're not anemic" while your ferritin sits at 15 and you feel like you're walking through wet sand.

Symptoms repeatedly associated with low-but-"normal" ferritin: persistent fatigue, exercise intolerance, hair shedding, brittle nails, restless legs, brain fog, and feeling cold. Menstruating women are by far the most affected group; endurance athletes and frequent blood donors follow.

Reading the numbers

• < 15–30 ng/mL — depleted stores; most guidelines treat this as iron deficiency even without anemia.
• 30–50 ng/mL — a gray zone where symptomatic people often benefit from repletion; this is the band Bariva flags when your goals include energy or hair.
• > 150–200 ng/mL (women) / > 300 (men) — investigate before touching iron: inflammation, liver issues, or hereditary hemochromatosis can all be behind it.

One interpretation trap: ferritin is an acute-phase protein — inflammation inflates it. A "fine" ferritin next to an elevated CRP can still hide iron deficiency.

Supplementing without the stomachache

• Form matters. Iron bisglycinate is markedly gentler on the gut than ferrous sulfate at comparable effect; it's the form worth paying a little more for.
• Every-other-day may beat daily. Iron absorption is throttled by hepcidin, which spikes for ~24h after a dose. Alternate-day dosing raises absorption per pill and cuts side effects.
• Timing: away from coffee, tea, calcium, and dairy (all block absorption); vitamin C or an empty-ish stomach helps.
• Retest in ~3 months. Ferritin climbs slowly; that's the checkpoint that tells you the protocol works.