Iron Deficiency: Symptoms, Who Is Low, and the Test
The signs of low iron are vague; a ferritin blood test is how you know. About 1 in 5 US women aged 18 to 49 have used-up iron stores (CDC tests, 2021–2023). Men rarely do, so low iron in a man, or a woman past menopause, needs a doctor to find the cause.
By Erin Rose Updated October 6, 2026 How we score
Symptoms: what low iron does
Stores fall first and silently; hemoglobin falls only once they are used up. These symptoms have trial or study evidence, and each one is shared with other conditions.
| Symptom | What the evidence shows | Verdict |
|---|---|---|
| Tiredness without anemia | In 198 women with fatigue, ferritin under 50 and normal hemoglobin, 80 mg of iron a day for 12 weeks cut fatigue scores by 48%, against 29% on a placebo (Vaucher 2012). An earlier trial in 144 women found the same, and only women with ferritin of 50 or below improved (Verdon 2003). | Real, but shared with many conditions |
| Restless legs | A Cochrane review found iron improved restless legs over a placebo (Trotti 2019). An international guideline rates oral iron as possibly effective when ferritin is 75 or below (Allen 2018). | Real; iron helps when ferritin is low |
| Craving ice (pica) | Among 55 patients with iron-deficiency anemia from gut bleeding, 58% had pica, and in most of them it was ice-eating (Rector 1989). | Real; common in iron-deficiency anemia |
| Less stamina for exercise | In iron-deficient endurance athletes without anemia, iron raised ferritin and aerobic capacity (Burden 2015). In adults low in iron but without anemia, it did not change measured capacity (Houston 2018). | Real in anemia and in athletes |
| Hair shedding | A controlled study found iron deficiency no more common in women with hair loss than in women without it (Olsen 2010); another found lower ferritin in two types of hair loss (Kantor 2003). Whether iron regrows hair is unknown. | A possible link, not a sign |
Tiredness plus a risk factor below, or restless legs or ice cravings on their own, make a ferritin test worth doing. No symptom justifies taking iron without the number.
Who is low
Mostly women of childbearing age. In the CDC’s 2021–2023 tests, 21.7% of women 18 to 49 had ferritin under 15 once adjusted for inflammation (13.9% as measured). That survey tested ferritin only in women 12 to 49 and young children, so for men and older women the latest figures are from 2017–2020:
| Item | Value |
|---|---|
| Women 18–39 | 13.3% |
| Women 40–59 | 10.4% |
| Women 60+ | 2% |
| Men 18–39 | 1.1% |
| Men 40–59 | 0.8% |
| Men 60+ | 1% |
How common low iron, vitamin D and other deficiencies are, with the method.
Who is at risk
| Risk factor | Why | Evidence |
|---|---|---|
| Periods, especially heavy ones | Monthly blood loss. | In 2021–2023 CDC tests, 21.7% of women 18–49 had used-up iron stores (our analysis). |
| Pregnancy | Needs rise to 27 mg a day (NIH). | In US national data, iron deficiency rose from 6.9% of pregnant women in the first trimester to 29.5% in the third (Mei 2011). |
| Giving blood | Each donation removes iron faster than food replaces it. | Among 2,425 US donors, 15.0% had absent iron stores, and 27.1% of frequent female donors (Cable 2011). |
| Vegetarian and vegan diets | No heme iron; plant iron is absorbed less well. | Across 24 studies, vegetarians had lower ferritin than non-vegetarians (Haider 2018). |
| Gut bleeding | Ulcers, polyps, cancers. | In 100 patients with iron-deficiency anemia, endoscopy found a lesion that could explain it in 62 (Rockey 1993). |
| Celiac disease | Damages the part of the gut that absorbs iron. | About 3% of people with iron-deficiency anemia had celiac disease in a review of 18 studies (Mahadev 2018). |
| Weight-loss surgery | Bypasses the main site of absorption. | Iron deficiency was found in 17% before surgery and 38% eight years after, across 57 studies (Xia 2023). |
| Acid-reducing drugs (PPIs) | Stomach acid helps absorb iron. | Two or more years of PPIs carried 2.5 times the odds of a new iron-deficiency diagnosis (Lam 2017). |
The test: ferritin, and the inflammation catch
Serum ferritin is the test. In a review of 55 studies against bone-marrow iron, the reference standard, it was the most accurate single blood test (Guyatt 1992). Hemoglobin is the wrong first test, because it stays normal until the stores are gone.
- Under 15 ng/mL: used-up stores in adults (WHO 2020; Daru 2017).
- Under 30 ng/mL: low stores in general (BSG 2021). Most labs set their normal range to start somewhere from 15 to 30, so a result in the 20s can be flagged normal.
- 50 or under: the entry line of the larger fatigue trial above (Vaucher 2012); in the other, only women at 50 or below improved (Verdon 2003). Not a deficiency line.
The catch: ferritin rises with inflammation, from an infection, a flare-up or liver disease, without adding any iron. In a review of 32 studies, inflammation raised ferritin by about 30% (Thurnham 2010). Ask for a CRP with the ferritin; if it is raised, a “normal” ferritin does not clear you. More on the ferritin test and its ranges.
If you are low
- How much: one 65 mg tablet a day, or every other day, is the standard (BSG 2021; AGA 2024). Our dosage guide.
- How long: hemoglobin usually rises within 2 weeks; keep going about 3 months after it is back to normal, to refill the stores (BSG 2021).
- Men and women past menopause: see a doctor, who will look for the cause, usually while you start iron. In about a third of them, iron-deficiency anemia comes from a disease that needs finding, most often in the gut (BSG 2021; Ko 2020).
- If oral iron fails or you cannot absorb it, as after weight-loss surgery, iron by drip is the next step (AGA 2024).
- Keep iron away from children. After the FDA required single-dose packaging in 1997, deaths from iron poisoning in young children fell sharply (Tenenbein 2005).
Questions
What are the first signs of iron deficiency?
Usually none you would notice. Ferritin, the stored iron, falls first while the blood count stays normal. Later come tiredness, less stamina, restless legs and, in some people, a craving to chew ice. Each has other causes, so the test decides.
What ferritin level means iron deficiency?
Under 15 ng/mL means the stores are used up in adults (WHO 2020). Many doctors treat anything under 30 as low. Ferritin rises with inflammation, so ask for a CRP test with it: a raised CRP can hide low iron behind a normal ferritin.
Can you be iron deficient without anemia?
Yes, and it is the more common state. The stores run down first; hemoglobin falls only once they are used up. The fatigue trials above were in women with low ferritin and normal hemoglobin.
Why should a man with low iron see a doctor first?
Men have no monthly blood loss, and in the CDC’s 2017–2020 tests no more than 1.1% of men in any age group had used-up stores. Low iron in a man, or a woman past menopause, often comes from blood loss, most often in the gut, and guidelines advise looking for the cause (BSG 2021; Ko 2020).
Should I take iron just in case?
No. The body loses very little iron, so extra can build up; the upper limit for adults is 45 mg a day, and iron pills are dangerous to small children. Test first.
Sources
- Vaucher P, et al. CMAJ. 2012. PubMed 22777991. Verdon F, et al. BMJ. 2003. PubMed 12763985. Houston BL, et al. BMJ Open. 2018. PubMed 29626044.
- Trotti LM, et al. Cochrane Database Syst Rev. 2019. PubMed 30609006. Allen RP, et al. Sleep Med. 2018. PubMed 29425576.
- Rector WG Jr. J Gen Intern Med. 1989. PubMed 2585159. Burden RJ, et al. Br J Sports Med. 2015. PubMed 25361786. Olsen EA, et al. J Am Acad Dermatol. 2010. PubMed 20947203. Kantor J, et al. J Invest Dermatol. 2003. PubMed 14708596.
- Mei Z, et al. Am J Clin Nutr. 2011. PubMed 21430118. Cable RG, et al. Transfusion. 2011. PubMed 20804527. Haider LM, et al. Crit Rev Food Sci Nutr. 2018. PubMed 27880062.
- Rockey DC, Cello JP. N Engl J Med. 1993. PubMed 8179652. Mahadev S, et al. Gastroenterology. 2018. PubMed 29689265. Xia C, et al. Obes Surg. 2023. PubMed 36701012. Lam JR, et al. Gastroenterology. 2017. PubMed 27890768.
- Guyatt GH, et al. J Gen Intern Med. 1992. PubMed 1487761. Daru J, et al. Am J Clin Nutr. 2017. PubMed 29070560. Thurnham DI, et al. Am J Clin Nutr. 2010. PubMed 20610634. World Health Organization. Guideline on ferritin concentrations to assess iron status. 2020.
- Snook J, et al. (BSG 2021). Gut. 2021. PubMed 34497146. Ko CW, et al. Gastroenterology. 2020. PubMed 32810434. DeLoughery TG, et al. Clin Gastroenterol Hepatol. 2024. PubMed 38864796. Tenenbein M. Arch Pediatr Adolesc Med. 2005. PubMed 15939855.
- CDC National Center for Health Statistics, NHANES 2017–March 2020 and August 2021–August 2023 (ferritin, CRP); our analysis, method on the deficiency page.
This page is for information. It is not medical advice.