Iron Supplements for Women: Why Most Forms Don't Work (And What to Take Instead)

My hair was falling out. I was exhausted by 2pm every day. My workouts felt harder than they used to, and I assumed it was stress, sleep, age. Then my doctor ran a full iron panel and found my ferritin was 9. (Optimal is 50-100+. Mine was 9.)

What followed was six months of figuring out why standard iron supplements weren't raising my levels -- and eventually finding a form that did.

The Problem With Standard Iron Supplements

Iron deficiency is the most common nutritional deficiency worldwide, affecting an estimated 1 in 5 women of reproductive age. The standard supplement doctors often recommend is ferrous sulfate (the "standard" iron). It's cheap and widely available. It's also notoriously hard on the gut.

Ferrous sulfate causes constipation, nausea, and abdominal cramping in a significant portion of users. The GI side effects are bad enough that many women stop taking it within weeks -- which means their iron never actually gets replenished.

The bigger issue is absorption. Standard iron supplements have poor bioavailability when taken with food (which you often need to do to avoid GI upset). You're in a catch-22: take with food to avoid nausea, but food reduces absorption.

Why Iron Bisglycinate Works Better

Iron bisglycinate is chelated iron -- the iron molecule is bound to glycine, an amino acid. This changes how it's absorbed: it enters through a different pathway than non-chelated iron, one that's less affected by other food components (including calcium, tannins from tea and coffee, and phytates from grains).

Clinical trials comparing ferrous bisglycinate to ferrous sulfate show similar efficacy for raising hemoglobin and ferritin, with significantly fewer GI side effects. The bisglycinate form is gentler because the chelation means the gut doesn't see free iron ions -- those are the irritants in standard iron supplements.

Thorne Iron Bisglycinate is the formulation I ended up using after trying two others. Thorne is NSF Certified for Sport, third-party tested, and their supplement forms consistently use the most bioavailable versions of each nutrient.

How I Finally Got My Ferritin Up

Thorne Iron Bisglycinate, 25mg, taken every other day (not daily -- recent research suggests every-other-day dosing improves absorption) on an empty stomach 30 minutes before coffee. I added 500mg vitamin C alongside it, since ascorbic acid significantly enhances non-heme iron absorption.

My ferritin went from 9 to 46 over four months. My hair stopped falling out. My afternoon energy came back. I still track ferritin every 3 months because I naturally tend toward deficiency.

A Direct Comparison

Signs You Might Be Iron Deficient

Get a full iron panel (ferritin, serum iron, TIBC, transferrin saturation) -- not just hemoglobin. Hemoglobin can look normal while ferritin is critically low. Symptoms that correlate with low ferritin even without anemia:

• Fatigue that sleep doesn't fix
• Increased hair shedding (especially postpartum or after heavy periods)
• Shortness of breath with exercise that used to be easy
• Cold hands and feet
• Restless legs, especially at night
• Difficulty concentrating ("brain fog")
• Pale inner eyelids or gums

Women at highest risk: menstruating women (especially heavy periods), postpartum women, vegetarians and vegans, athletes, and women with gut conditions affecting absorption.

Important Context Before Supplementing

Iron supplementation without confirmed deficiency is not recommended. Excess iron is actually harmful -- it's a pro-oxidant. Get your ferritin tested before starting, and retest every 3 months if supplementing to confirm you're trending in the right direction (and to know when to stop).

Also worth reading: postpartum hair loss is frequently iron-related -- see my postpartum hair loss guide for what actually helped.

The Bottom Line

If your doctor recommends iron and the standard ferrous sulfate is destroying your digestion, ask specifically about iron bisglycinate. Thorne Iron Bisglycinate is what I'd recommend: third-party tested, gentle form, effective dose. Take it every other day with vitamin C, away from coffee. Get your ferritin retested in 12 weeks. For most women with iron deficiency, this protocol actually works.