Iron deficiency without anemia and iron infusions, rethought
For the woman who, after the tenth "everything is in the normal range", still does not understand why she is so empty. And for everyone who wants to understand what the current evidence on iron deficiency without anemia shows, and which questions often fall short in everyday practice.
You are functioning. But inside, it has gone quiet.
I bet you know this feeling.
You get up in the morning and ask yourself why, after eight hours of sleep, you feel as if you had never slept. Why you feel cold although the heating is on. Why during your coffee break you think you are about to fall asleep if you sit down. Why you have no strength left in the evening to meet friends. Why your hair looks different from how it did two years ago. Why your legs start to tingle in the evening as soon as you come to rest.
And you went to the doctor. Maybe even twice, three times, four times. They drew your blood. The doctor nodded. She said: everything is in the normal range. Maybe she added that you should take it a bit easier. Maybe a little less stress. Maybe psychotherapy. Maybe magnesium. Maybe "this will pass with time".
And you drove home. Somehow relieved that nothing was found. And somehow more frustrated than before. Because you know: there is more. Your body is talking. And you do not understand it, because the language in which you are speaking is rougher than what your body is telling you.
You are not being dramatic. You are not weak. You are not "just stressed". What you experience often has a biochemical explanation. And in a surprisingly large share of cases this explanation has to do with iron.
Not too little iron in the sense of a classical anemia. But something that, in German medicine, was for a long time hardly noticed and is still far too often overlooked today: functional iron deficiency without anemia.
This article is for you, if for months or years you have been trying to understand why something is missing that you cannot name. It is also for you if you already know that you have an iron deficiency and ask yourself why the tablets never work the way you wish. And it is for you, if you are wondering whether an iron infusion could make sense for you.
What iron really does for you, every day, without you noticing.
Imagine your system not as a "body", but as a city. In this city there are streets, transport routes, lights, factories, warehouses, post offices. The main currency in this city is not money. The main currency is oxygen. Without it, everything stands still.
And iron is the material from which the containers are built that transport oxygen. Imagine iron as the small trucks of your body. Without trucks, the goods stay in the harbor. The factories starve. The city becomes slower, quieter, paler.
Iron sits in your red blood cells, in hemoglobin, and brings oxygen from your lungs to every single cell. It sits in your muscles, in myoglobin. It is in hundreds of enzymes that pull energy from your food. It is part of the enzymes that sit in the mitochondria of every one of your cells, the small power plants.
Iron is also in the brain. Very prominently in fact. It is a cofactor in the production of dopamine and serotonin. It is involved in building the myelin sheath that wraps around your nerves.
Iron is involved with the thyroid. Thyroid peroxidase, a key enzyme that builds your thyroid hormones, needs iron as a heme cofactor. Iron is involved in the immune system. And iron is also involved in heat regulation. That can explain why many people with iron deficiency feel cold more often. There are other reasons to feel cold, for example the thyroid or circulation. But your feeling cold is not an imagination problem. It is a finding that can be worked up.
Iron is not a "vitamin for strong people". It is the raw material on which your entire energy economy stands. When iron is missing, your blood values are not the first to notice. Your mitochondria notice. Your brain. Your thyroid. Your hair. Your mood. Your nights.
Three words that confuse everything: hemoglobin, ferritin, reference range.
Hemoglobin: the red pigment that carries oxygen.
Hemoglobin is the protein that sits in your red blood cells and binds oxygen. When your hemoglobin drops, this has a name: anemia. The WHO defines this in women as hemoglobin under 12 grams per deciliter.
But: hemoglobin is the last bastion to fall. Your body holds hemoglobin at normal level for as long as possible, even when inside there has long been an alarm. When your hemoglobin falls, the barrel has been empty for months.
Ferritin: the warehouse no one looks at.
Ferritin is your iron storage. The central warehouse of your city. Ferritin falls long before hemoglobin falls. Ferritin is the early warning value.
The reference range: a statistic that is often read as a verdict.
A reference range is not a medical truth. It is a statistic. It describes how 95 percent of values in a studied population look. Typical ferritin reference range for women in German labs: 15 to 150 micrograms per liter. So a value of 18 will be printed as "within the normal range".
Several recent works show that symptoms can already arise at ferritin between 15 and 50 micrograms per liter. Part of the professional community proposes a target range of 50 to 100 micrograms per liter for symptomatic women. A binding threshold for this does not exist so far.
"Within the normal range" does not automatically mean "optimal for you". It means: you are in the statistical majority. Whether your body still works well in this zone is a completely different question.
A woman comes to the consultation because she has been exhausted for months. Hemoglobin was unremarkable every time. Ferritin was either not measured at all or commented on as "unremarkable". Only when you look at ferritin, transferrin saturation and an inflammation marker together, and add the cycle history, does the picture become more complete.
I deliberately describe only the pattern here and no individual case with values and outcome. How a workup turns out differs from person to person and cannot be promised in advance.
What is functional iron deficiency really?
The term functional iron deficiency describes a state in which your body suffers from iron deficiency consequences, in which typical lab parameters point to a deficit, but in which hemoglobin has not yet fallen into the classical anemia zone. Reviews assume that iron deficiency without anemia is clearly more common than classical iron deficiency anemia. How much more common depends strongly on which threshold is applied.
Who is especially at risk
- Women with strong or long menstruation. Every bleeding is iron loss.
- Endometriosis patients. Heavy bleeding and chronic inflammation can come together here.
- Female athletes and active women. Load, sweat losses and micro-bleeding can raise the requirement.
- Women on a vegetarian or vegan diet. Plant iron is absorbed less well.
- People with chronic gut problems. Celiac disease, gastritis, IBD, post-stomach surgery.
- Pregnant and breastfeeding women. Iron requirement nearly doubles.
- Women in menopause. Hormonal bleeding irregularities.
- People with silent inflammation. Hepcidin blocks iron absorption.
Iron deficiency in menstruating women is not the exception. It is common. And still, in everyday practice it is often treated as if it were a curiosity. It is worth looking more closely.
How does a functional iron deficiency really feel?
The quiet exhaustion that does not fit the stress.
"I am tired faster than I used to be, although I do not do more." Your mitochondria work with less iron than they need. You build the same energy currency, but at higher "cost".
The cognitive level: brain fog.
Your brain is a high-performance, hungry organ. Two percent of your body weight, but twenty percent of your oxygen consumption. Iron is a cofactor in dopamine production, serotonin production and myelination.
A meta-analysis from 2025 pools 18 studies with 1,408 participants without anemia.
Core finding: in the randomized studies iron supplementation could improve cognitive test performance (d = 0.46), short-term memory (d = 0.53), fatigue (d = 0.34) and anxiety (d = 0.34). For attention and depression there was no significant effect. The effect sizes come from mostly small studies. The authors therefore word it cautiously: iron deficiency may affect brain function even before anemia.
Fiani D et al. Neurosci Biobehav Rev. 2025;178:106372. DOI: 10.1016/j.neubiorev.2025.106372The cold. The hair. The thyroid.
Iron is involved in thermoregulation. It needs oxygen to produce heat.
Treister-Goltzman 2022: meta-analysis over 36 studies with more than 10,000 women.
Core finding: women with non-scarring hair loss had on average lower ferritin values, with a pooled mean difference of 18.5 ng/dL. In 21 percent ferritin lay clearly below typical thresholds.
Important for context: this is an association and not proof of cause and effect. The authors state explicitly that the evidence is not conclusive. Whether hair loss improves by refilling the iron stores is therefore not established.
Treister-Goltzman Y et al. Skin Appendage Disord. 2022;8(2):83–92. DOI: 10.1159/000519952Restless legs syndrome: when your legs do not come to rest at night.
RLS is a neurological condition in which a disturbed dopamine function in the brain plays a central role. Studies with high-resolution magnetic resonance imaging suggest that a part of those affected have less iron in certain brain regions, even when ferritin in the blood is unremarkable. The findings are not uniform, and no treatment decision can be derived from an imaging finding alone.
Khan 2025: systematic review with meta-analysis over seven studies with 539 participants.
Core finding: symptom intensity (IRLS score) sank under intravenous ferric carboxymaltose compared to placebo by an average of 5.77 points. RLS-related quality of life, by contrast, did not improve significantly, and adverse events, above all nausea, were more frequent under iron.
In its 2018 task force report the international RLS study group states that intravenous iron can be considered as first-line treatment in moderate to severe RLS with a ferritin under 300 micrograms per liter. That is a may-option after medical weighing, not an automatism for every form of restless legs.
Khan A et al. Front Neurol. 2025;15:1503342. DOI: 10.3389/fneur.2024.1503342 · Allen RP et al. Sleep Med. 2018;41:27-44. DOI: 10.1016/j.sleep.2017.11.1126If you have had restless legs for years and were told you should "relax": your brain can be hungry for iron, even when your blood is not. This is not esoterics. This is modern neurology.
The period. The thyroid. The mood.
A normal menstruation loses 15 to 20 milligrams of iron. A heavy one loses double to triple that. The enzyme thyroid peroxidase needs iron as a heme cofactor. The dopamine and serotonin system, which carries your mood, needs iron.
Exhaustion and low mood have many possible reasons. Iron deficiency can be one of them and is worth working up. But it does not replace a psychiatric or psychotherapeutic assessment. In the meta-analysis named above, depression did not improve significantly with iron. Checking iron alongside remains sensible, because it is simple and can clarify part of the picture.
The hepcidin puzzle: why more iron often does not mean more effect.
Hepcidin is a hormone that your liver makes. A kind of doorman for iron. When hepcidin is high, the door closes. No matter how much iron you eat or swallow, it does not arrive.
- When you have just received iron. After an oral tablet, hepcidin rises for up to 24 hours.
- When you have a silent inflammation. Chronic processes keep hepcidin permanently elevated.
- After strong physical exertion. Especially relevant for athletes.
Stoffel and Moretti at ETH Zürich studied iron absorption in iron-deficient young women.
Core finding: cumulative absorption was higher when there was a free day between the doses (175.3 mg versus 131.0 mg). Hepcidin rose with daily dosing, which can reduce the absorption of subsequent doses. For splitting into two daily doses the same work found no significant difference. The authors note that the findings still have to be confirmed in anemic patients.
Stoffel NU et al. Lancet Haematol. 2017;4(11):e524–e533. DOI: 10.1016/S2352-3026(17)30182-5If you have swallowed iron daily for years and it "did nothing", it was not necessarily the wrong preparation. It can simply be that the timing was biologically unfavorable.
Cofactors that let iron actually work
- Vitamin C: increases iron absorption.
- Copper: contributes to normal iron transport in the body.
- Riboflavin, B6, B12, folate: contribute to normal blood formation.
- Vitamin A: a role in mobilizing iron from storage is discussed. There is no established statement on this.
- Protein: transferrin and ferritin are protein molecules.
Whether and what you need of this should follow from your values and not from a list.
A gap in everyday care: why young women so often slip through.
Imagine a young woman. Mid-twenties, early thirties. She functions. But inside she is empty. She goes to the doctor. Hemoglobin: 12.3. Ferritin, if measured at all: 21. "All within the normal range."
I meet this situation often. How common it is in the population depends strongly on the chosen threshold. That is why I give no figure here.
You are not unreliable. You are not too sensitive. You are not hysterical. Those are words that have been given to women for centuries when medicine did not know any further. Your body speaks a precise biochemical language. If no one translates it, the fault does not lie with you.
The tablet dead end.
Oral iron can burden the gastrointestinal tract. A meta-analysis over 43 randomized trials with 6,831 adults found a clearly increased risk of gastrointestinal complaints under ferrous sulfate compared with placebo (odds ratio 2.32). Many therefore drop out of therapy early. Tolkien Z et al. PLoS One. 2015;10(2):e0117383. DOI: 10.1371/journal.pone.0117383
Typical reasons why tablets do not arrive
- Gastritis or post-stomach surgery.
- Inflammatory bowel disease.
- Celiac disease or gluten sensitivity.
- Long-term intake of PPI.
- Helicobacter pylori infection.
- Chronic inflammation of any kind.
A normal iron tablet delivers 40 to 100 milligrams of iron, of which 10 to 20 percent is absorbed (4 to 20 mg per day). A woman with a strong period loses 30 to 50 milligrams per cycle.
Oral iron therapy often fails not because of you. It fails because of biology, pharmacology and mathematics, all at once.
Iron infusions: old fears, new reality.
Today's preparations have almost nothing more in common with their predecessors from the 1970s. They are wrapped in stable carbohydrate cages, systematically tested in approval studies with thousands of patients.
Modern IV iron preparations in Germany
- In Germany several modern intravenous iron preparations are available. They differ in the maximum dose per session and in infusion time.
- Which preparation comes into question for you is a medical decision and is discussed in the consultation. That is why I deliberately give no product names and no dose figures here.
- All intravenous iron preparations are prescription-only medicines and belong in medical hands.
Three advantages over tablets: independent of gut function, independent of hepcidin, storage is filled quickly. That does not mean every woman with low ferritin needs an infusion.
What the major studies really show.
Favrat 2014 (PREFER): randomized, placebo-controlled, single-blind study in 290 women with ferritin under 50 and transferrin saturation under 20 percent (or ferritin under 15), without anemia. Funded by the manufacturer of the preparation used.
Core finding: in the iron group, fatigue was clinically relevantly improved in 65.3 percent, compared with 52.7 percent under placebo. Important for context: adverse events occurred almost twice as often under iron as under placebo (209 versus 114), mostly mild to moderate.
Favrat B et al. PLoS One. 2014;9(4):e94217. DOI: 10.1371/journal.pone.0094217Krayenbuehl 2011: 90 premenopausal, non-anemic women with fatigue, ferritin at or under 50.
Core finding: across the whole group the study narrowly missed its endpoint (decline of 1.1 versus 0.7 points, p = 0.07). A clear effect showed only in the women whose ferritin was at 15 or below. The authors state that the benefit was bound to this low ferritin value. That is an important damper: the closer your ferritin is to the normal range, the less certain the benefit of an infusion. Adverse events were more frequent under iron (21 percent versus 7 percent).
Krayenbuehl PA et al. Blood. 2011;118(12):3222–3227. DOI: 10.1182/blood-2011-04-346304Houston 2018: systematic review on iron supplementation in non-anemic deficiency.
Core finding: clinically relevant improvement of subjective fatigue (SMD −0.38). The objective physical performance did not improve significantly.
Houston BL et al. BMJ Open. 2018;8(4):e019240. DOI: 10.1136/bmjopen-2017-019240Iron can help with fatigue as a subjective experience, when a deficit is present. Iron is no performance enhancer for people who are already well supplied. It is a tool for refilling a deficit, not for raising above the normal level.
Afolabi 2024: over 1,000 pregnant women in Nigeria with iron deficiency anemia randomized.
Core finding: the anemia rate at week 36 was similar (58 percent intravenous versus 61 percent oral). The prevalence of iron deficiency fell further in the infusion group. The trial was open-label, so not blinded, and studied anemic pregnant women in Nigeria. It cannot be transferred to a woman with ferritin around 25 and no anemia.
Afolabi BB et al. Lancet Glob Health. 2024;12(10):e1649–e1659. DOI: 10.1016/S2214-109X(24)00239-0Safety of modern iron infusions.
Achebe 2020: analysis of five randomized head-to-head trials with 5,247 treated patients.
Core finding: the rate of serious, or moderate to severe, hypersensitivity reactions lay between 0.2 and 1.7 percent depending on the preparation. That is low, but it is not zero. That is why every iron infusion belongs in a setting with emergency equipment, trained staff and post-infusion observation. In case of breathing difficulty, facial swelling or circulatory collapse after an infusion, call the emergency number 112 and not the next practice appointment.
Achebe M, DeLoughery TG. Transfusion. 2020;60(6):1154–1159. DOI: 10.1111/trf.15837What was seen in clinical studies
- Mild reactions: skin redness, itching, headaches, nausea, metallic taste.
- Local side effects: hematoma or skin discoloration (rare).
- Fishbane reaction: brief warmth, facial flushing, pressure on the chest or back during the infusion. It usually settles when the infusion is paused, but is often experienced as an emergency.
- Severe allergic reactions: rare, but possible. Hence at least 30 minutes of observation and emergency equipment in the room.
Hypophosphatemia
Ferric carboxymaltose can lower the phosphate level in the blood. Mostly this resolves. But there are regulatory safety notices on severe and persistent hypophosphatemia, which in individual cases can lead to bone softening (osteomalacia) and to stress fractures, above all with repeated high doses. There are differences in risk between the substances. From that, however, no certainty can be derived for the individual case. That is why I check phosphate and repeat an infusion only on the basis of current laboratory values. If you notice new bone or muscle pain after an infusion, please get in touch.
When I do not give an infusion
- No clear iron deficiency documented.
- Acute infection or high CRP.
- Severe kidney or liver disease.
- Oral therapy is functioning sufficiently.
The path in my practice.
The conversation
A good appointment begins with a thorough conversation about your story, bleeding, nutrition, digestion, sleep, stress.
Physical examination and functional diagnostics
Physical examination. Additional measurements such as bioimpedance analysis or heart rate variability I order only when they contribute something to your question. For iron deficiency diagnostics itself they are not required.
Targeted laboratory diagnostics
The core is lean: blood count, ferritin, transferrin saturation and an inflammation marker. These four values clarify most cases. Everything beyond that I order only when your history or an abnormal finding justifies it. A broad panel is not a quality feature.
Special diagnostics as needed
Only with a concrete question, for example extended gut diagnostics in therapy-resistant deficiency. For wider analyses within iron deficiency diagnostics there is no evidence of benefit, so I do not propose them routinely.
The treatment decision
Combination of root-cause work, nutrition, cleverly timed oral therapy and lifestyle changes. Iron infusion when needed.
The iron-deficiency lab
The first five rows are the core. Everything below them I order only when your history or an abnormal value gives a reason for it.
| Parameter | What it shows |
|---|---|
| Hemoglobin, MCV, MCH | Classical blood count |
| Ferritin | Iron storage (acute-phase protein) |
| Transferrin saturation | Loading of the transport protein |
| Soluble transferrin receptor (sTfR) | Cell hunger for iron, independent of inflammation |
| High-sensitivity CRP | Inflammation marker for ferritin context |
| Reticulocyte hemoglobin | Early marker for therapy effect |
| Vitamin D (25-OH) | Immunomodulator |
| Vitamin B12, holo-TC | Neurological, blood formation |
| Folate | Blood formation |
| TSH, fT3, fT4, TPO antibodies | Thyroid and autoimmune picture |
| Fasting insulin, HbA1c | Metabolic picture |
| Celiac screening | In therapy-resistant deficiency |
The seven doctors of lifestyle.
Nutrition
Heme iron from meat, poultry, fish is absorbed 2–3 times better than plant iron. Coffee and tea slow absorption with the meal.
Sleep
Blood formation follows a daily rhythm. Lack of sleep can influence iron metabolism too, via inflammatory signalling. Studies on this are thin, I am describing a physiological consideration here. Getting morning daylight into your eyes helps the rhythm.
Movement
Gentle to moderate movement improves absorption conditions. McCormick 2019: iron absorption better in the morning after training than in the evening.
Breathing and nervous system
10 minutes of slow belly breathing daily (4 sec in, 6–7 sec out) can activate the vagus nerve and dampen inflammatory signalling.
Warmth, light, nature
Warm foot baths, cherry stone pillows, sauna. Sunlight for vitamin D.
Relationship
Chronic loneliness is associated with raised inflammation markers. Whether regeneration measurably improves as a result is not settled. I am describing a clinical observation here, not a study finding.
Meaning
Why do you want to get well? Without a clear "why", every resolution breaks after three weeks.
An individual case with laboratory values and outcome used to stand in this place. I have removed it. A single story raises the expectation that it will go the same way for you. That expectation I cannot honor.
What I can say: a structured approach begins with the search for causes, then with a carefully timed oral attempt. Only when that is not enough or is not tolerated does an infusion come up for discussion. How your body responds is open.
How does an iron infusion work?
Preparation
Current lab, medications, allergies. Dose calculation (500–1,500 mg).
Information and consent
Benefit, risks, alternatives. No signature without all answers.
The infusion
Small venous access, 15–45 minutes depending on the preparation.
Monitoring
Vital signs checked, team nearby.
After the infusion
30 minutes of observation, then home.
Follow-up
After 6–8 weeks ferritin, transferrin saturation, phosphate.
The infusion is the beginning, not the end.
An infusion fills the tank. But if there is a hole in the tank, it will be empty again. My task is to find the hole.
The most important leaks
- Heavy menstruation. Gynecological workup.
- Gastrointestinal losses. Important in men and postmenopausal women.
- Silent inflammation. Chronic stress, autoimmune processes.
- Absorption disorders. Celiac disease, gastritis, PPI, IBD.
- Nutritional gaps. Too little heme iron, too little protein.
"My goal is that one day you do not need me anymore. Not that you come for an infusion every six months. My goal is that your system is so stable again that you handle it well yourself."
My vision: medicine that one day no longer needs you.
Three basic principles:
Nutrition as foundation. Iron, protein, micronutrients. A plan that fits your everyday life.
Gut and absorption function. Even the best nutrition brings little if the gut cannot use it.
Lifestyle as therapy. When the seven doctors of lifestyle work together, many therapies can become unnecessary.
Your self-check.
Block 1: symptoms
- You are often tired even though you sleep enough.
- You wake up in the morning and feel unrested.
- You feel cold faster than you used to.
- Your hair feels thinner, more shedding.
- Your nails are brittle.
- You have restless legs at night, tingling.
- Your head is often "foggy".
- You are more irritable or low.
- Dizziness on standing up, new or stronger.
- Frequent headaches.
- Your skin has become paler.
Block 2: risk factors
- You menstruate strongly or for a long time.
- Endometriosis, fibroids or copper IUD.
- Vegetarian, vegan or little red meat.
- Pregnancies in the past years.
- Regular intense endurance sport.
- Chronic gut disease.
- Regular PPI intake.
- Celiac disease or gluten sensitivity.
- Stomach or gut surgery.
- Hypothyroidism or autoimmune disease.
- Pronounced chronic stress.
Block 3: history so far
- You have the feeling "something is off", but you were told everything is normal.
- Iron tablets did not help or were not tolerated.
- For years the same answers, nothing changes.
- Ferritin has never been measured.
- You are wondering whether an iron infusion could help you.
At least three points from Block 1 plus one from Block 2: an iron deficiency workup can be sensible. This self-check is not a validated screening instrument. It makes no diagnosis and gives no result, it only sorts your observations for the conversation. This is no judgment about you. It is an invitation to look more closely.
Frequent questions, honestly answered.
Three concrete next steps.
Observe yourself for a week
Simple notes. When are you tired, when awake? A week of listening teaches you more than five lab tests without context.
Complete lab
Not only hemoglobin and ferritin. Have ferritin, transferrin saturation and CRP measured together.
Have your values explained
"All normal" is no explanation. You have a right to understand what the numbers mean in your life.
You are not alone with what you feel. And you are not crazy because you know there is more. You are simply someone who does not look away. That is rare. And it is brave. And your body knows it. It will thank you.
Sources and further reading
- Favrat B et al. PLoS One. 2014;9(4):e94217. DOI: 10.1371/journal.pone.0094217
- Krayenbuehl PA et al. Blood. 2011;118(12):3222–3227. DOI: 10.1182/blood-2011-04-346304
- Verdon F et al. BMJ. 2003;326(7399):1124. DOI: 10.1136/bmj.326.7399.1124
- Houston BL et al. BMJ Open. 2018;8(4):e019240. DOI: 10.1136/bmjopen-2017-019240
- Fiani D et al. Neurosci Biobehav Rev. 2025;178:106372. DOI: 10.1016/j.neubiorev.2025.106372
- Treister-Goltzman Y et al. Skin Appendage Disord. 2022;8(2):83–92. DOI: 10.1159/000519952
- Khan A et al. Front Neurol. 2025;15:1503342. DOI: 10.3389/fneur.2024.1503342
- Stoffel NU et al. Lancet Haematol. 2017;4(11):e524–e533. DOI: 10.1016/S2352-3026(17)30182-5
- Achebe M, DeLoughery TG. Transfusion. 2020;60(6):1154–1159. DOI: 10.1111/trf.15837
- Aung T et al. Korean J Fam Med. 2023;44(6):350–354. DOI: 10.4082/kjfm.23.0039
- Afolabi BB et al. Lancet Glob Health. 2024;12(10):e1649–e1659. DOI: 10.1016/S2214-109X(24)00239-0
- Allen RP, Earley CJ. Mov Disord. 2007;22 Suppl 18:S440–8. DOI: 10.1002/mds.21607
- Onkopedia guideline iron deficiency and iron deficiency anemia, DGHO, April 2025.
- Camaschella C. Blood. 2019;133(1):30–39. DOI: 10.1182/blood-2018-05-815944
- Ganz T. Blood. 2011;117(17):4425–33. DOI: 10.1182/blood-2011-01-258467
- McCormick R et al. Med Sci Sports Exerc. 2019;51(10):2147–2155. DOI: 10.1249/MSS.0000000000002026
- Breymann C. Semin Hematol. 2015;52(4):339–47. DOI: 10.1053/j.seminhematol.2015.07.003
- Allen RP et al. Sleep Med. 2018;41:27–44. DOI: 10.1016/j.sleep.2017.11.1126
- Tolkien Z et al. PLoS One. 2015;10(2):e0117383. DOI: 10.1371/journal.pone.0117383