doctor examining woman's eyelid for signs of anemia

Iron plays a number of important roles in the body, including helping red blood cells transport oxygen, according to the National Institutes of Health. It’s also critical for growth, muscle and nerve function, and the creation of certain hormones. Adult men and postmenopausal women need only 8 milligrams a day, while menstruating women need 18 milligrams, pregnant women need 27 milligrams, and breastfeeding mothers need 9 milligrams.

Nevertheless, iron deficiency is extremely common. According to WebMD, 20 percent of non-pregnant women, 50 percent of pregnant women, and 3 percent of men don’t get enough of this essential mineral.

The Mayo Clinic outlined four potential causes of iron deficiency. Some individuals, particularly vegetarians and vegans, may not get enough iron in their diet, while others may have difficulty absorbing iron because of gastrointestinal surgery or a condition such as celiac disease. A temporary increase in iron needs, such as during pregnancy, can also lead to deficiency. Lastly, blood loss (from a heavy period, ulcer, physical trauma, et cetera) can also rapidly deplete iron stores. Because iron is so important for health, a deficiency can cause a number of subtle and not-so-subtle symptoms that you should keep an eye out for.

Extreme fatigue can result from a lack of iron

woman with extreme fatigue

Iron’s most important role is as a component of hemoglobin, a protein found in red blood cells, a report in Proceedings explained. Hemoglobin picks up oxygen as it travels through arteries, delivering it to every cell in the body, where it’s used to help extract energy from the food we eat. Then, as it travels through the veins, hemoglobin binds to carbon dioxide and brings this waste product to the lungs, where it’s exhaled. Adults have 3 to 4 grams of iron in their bodies, and most of this is in hemoglobin, according to the National Institutes of Health.

Since iron is at the heart of every hemoglobin molecule, low iron levels will eventually lead to low hemoglobin levels, which is known as anemia. Iron deficiency is the most common cause of anemia, but there are other conditions and deficiencies that can cause low hemoglobin. If you’re anemic, you may experience severe fatigue, according to the Mayo Clinic. At the cellular level, your body just isn’t getting the oxygen it needs to produce energy.

You may have an iron deficiency if you experience shortness of breath

Because iron is needed to form hemoglobin, and hemoglobin transports oxygen throughout the body, iron deficiency anemia can leave you feeling easily winded. Your heart and lungs have to work extra hard to make up for the low hemoglobin and get enough oxygen to the body’s cells.

Although hemoglobin levels are often tested to check for anemia, this isn’t the only test medical professionals use. According to the Mayo Clinic, doctors may examine the size and color of red blood cells, since those in anemic individuals are smaller and paler. Hematocrit, the percentage of blood volume made up of red blood cells, is also often tested, since lower values indicate a lack of healthy red blood cells. Normal hematocrit ranges between 38.3 and 48.6 percent in adult men and 35.5 and 44.9 percent in adult women.

Lastly, doctors may also check a patient’s ferritin, a protein that binds to iron and allows the body to store it for future use. Normal ferritin ranges from 24 to 336 micrograms per liter in men and 11 to 307 micrograms per liter in women. Low ferritin levels mean your body’s iron reserves are likewise low. According to the Iron Disorders Institute, individuals can be iron deficient (that is, have a low ferritin level) without yet being anemic.

Weak muscles can be a sign of low iron

Iron is an essential component of another important protein: myoglobin. Myoglobin is similar to hemoglobin in that it has a ring of iron molecules at its center and helps transport oxygen, a report published in StatPearls explained. But unlike hemoglobin, which travels on red blood cells throughout the body, myoglobin is found only in muscle tissue. It’s present in skeletal muscles, cardiac muscle, and to a lesser degree, in the smooth muscle that lines your gastrointestinal tract. It delivers oxygen to muscle cells, particularly when they’re being strained (during exercise, for example).

Myoglobin also helps break down nitric oxide, a waste product that builds up in muscle cells. If you’re low on iron, you may be low on both myoglobin and hemoglobin, according to WebMD. And you’ll probably feel it in the form of weakness (via Healthline).

Even though muscle weakness is a common symptom of iron deficiency anemia, doctors rarely test myoglobin levels to diagnose anemia. A myoglobin test is most often performed as a way to gauge if someone has had a heart attack, since levels can be abnormally high in the hours after the heart (or any other muscle) is damaged.

Heart problems can point to a lack of iron

Iron deficiency anemia can have serious, even potentially life-threatening, consequences for your heart. Individuals may experience an irregular or faster-than-normal heartbeat. As the Mayo Clinic explained, "When you’re anemic your heart must pump more blood to make up for the lack of oxygen in the blood." Over time, untreated anemia can lead to an enlarged heart or heart failure.

One 2006 paper published in the Texas Heart Institute Journal reported that between one-third and two-thirds of patients with severe anemia had enlarged hearts, and the left ventricle (the chamber of the heart that pumps oxygen-rich blood into the body) was the area of the heart most likely to be affected. Fortunately, the researchers also noted that heart size and function returned to normal within a few weeks of treating the anemia.

But it’s a two-way street when it comes to iron and the health of your heart. Low iron can cause heart problems, and heart problems may increase the likelihood that an individual will be iron deficient. A study published in 2013 in the American Heart Journal found that iron deficiency was common in people with chronic heart failure and correlated to the severity of their condition. It is also an "independent predictor of worse functional capacity and survival," per the American College of Cardiology.

Feeling cold often may be a sign that you need more iron

Being low on iron can leave you feeling frigid, according to Healthline. "Some people may feel the cold more easily in general or have cold hands and feet," the site explained.

Animal research published in the American Journal of Physiology provided a possible explanation for reduced cold tolerance in anemic humans. When the thyroid doesn’t get enough oxygen because of low hemoglobin levels, it can’t produce T3 (thyroxine) and T4 (triiodothyronine), hormones that control body temperature. In addition, if the pituitary gland doesn’t receive adequate oxygen, it won’t be able to produce enough thyroid-stimulating hormone (TSH), which tells the thyroid to crank up its production of T3 and T4.

These findings were supported in a small study of iron-deficient and anemic women. Researchers found that the women’s body temperatures were lower than the control group’s at baseline and after 100 minutes of cold exposure. Their T3 and T4 levels were considerably lower as well.

An iron deficiency may be making your migraines worse

If you’re a woman who gets migraine headaches, being deficient in iron may make attacks more frequent or severe. A 2019 study published in the International Journal of Hematology-Oncology and Stem Cell Research attempted to discover the link between the two. Among study participants, women with low hemoglobin, low iron stores, or iron deficiency anemia were more likely to experience migraines. But the same link wasn’t found among male participants.

The researchers found that among migraineurs, iron concentrations were actually high in certain areas of the brain. So then how can low iron levels make someone more likely to have a migraine attack? One possible explanation is that iron is needed to make the neurotransmitter serotonin, and migraines are characterized by a drop in serotonin in the brain, the journal explained.

The researchers also hypothesized that lower levels of hemoglobin and ferritin in the blood may actually trigger the brain to increase its uptake of iron. As far as why women seem to be more affected than men, the researchers suggested that falling estrogen levels before a period can interfere with how the body absorbs and stores iron. As such, iron supplementation may help prevent or treat migraines.

A weakened immune system can be a sign that you’re low on iron

Although vitamin C gets all the attention when it comes to keeping your immune system strong, iron is just as important. Being iron deficient can weaken your immune system, but the relationship between the two is a bit complicated.

A 2010 paper published in the journal Basic Neurosciences, Genetics and Immunology explained that iron levels in the body are important because both our own immune cells and bacterial cells need iron for growth. The genes and proteins that control iron balance in the body can produce temporary fluctuations in iron in a way that prevents invading bacteria from using it. The authors noted that both iron deficiency and iron overload can disrupt this process, making the body more susceptible to bacterial infections.

In another paper, published in 2011, researchers demonstrated that chronic inflammatory conditions (think: diabetes, heart disease, arthritis, Crohn’s disease, et cetera) can lead to low iron levels. This is known as anemia of chronic disease. And unfortunately, this type of anemia doesn’t respond well to oral iron supplements

Restless leg syndrome can be a sign of low iron

"Restless legs syndrome (RLS) is a condition that causes an uncontrollable urge to move your legs, usually because of an uncomfortable sensation," according to the Mayo Clinic. This uncomfortable sensation, which is usually felt within the leg rather than on the skin, can take many forms including creeping, throbbing, aching, itching, or an electric tingle. Symptoms usually happen when at rest — particularly when lying down at night — and can temporarily be relieved by movement. RLS can make it difficult to fall and stay asleep. Although the exact cause of RLS is unknown, researchers believe it may be due to an imbalance in the neurotransmitter dopamine.

Iron deficiency (even without anemia) is considered a risk factor for RLS. This makes sense considering iron is needed to convert the amino acid tyrosine to dopamine. A 2013 study published in the American Journal of Hematology surveyed patients with iron deficiency anemia and found that nearly 24 percent had RLS. That is "nine times higher than the general population," per the study. Individuals with both anemia and RLS reported less and poorer quality sleep, decreased energy, and increased tiredness. Considering anemia can cause fatigue and low energy all by itself, having RLS is a double whammy.

If you’re low on iron, you may be depressed

Symptoms of anemia may leave you feeling down and discouraged, but even by simply being anemic, you may also be more at risk for depression. According to research cited by Science Daily, your body needs iron to synthesize the neurotransmitters dopamine and serotonin. These two chemicals are closely associated with depression. As Healthline explained, "Dopamine system dysfunction is linked to certain symptoms of depression, such as low motivation. Serotonin is involved in how you process your emotions, which can affect your overall mood."

In a 2018 study published in Psychiatry and Clinical Neuroscience, researchers gave nearly 12,000 Japanese participants questionnaires to see if there was a link between iron deficiency anemia (IDA) and depression. Among men, IDA was present in 7.2 percent of depressed individuals but only 4 percent of non-depressed subjects. Among women, 33.4 percent of depressed individuals had IDA, whereas 25.8 percent of non-depressed women had the condition.

The link between this type of anemia and depression may be especially strong for new mothers, since pregnancy often depletes iron stores. A literature review published in 2019 in the Journal of Psychosomatic Obstetrics and Gynecology concluded,"[Anemia] and/or iron-deficiency may contribute to PPD [postpartum depression] in at-risk women."

Your nails may be trying to tell you that you need more iron

The eyes may be the windows to the soul, but your fingernails are what give you a glimpse into what’s going on elsewhere in your body. This is certainly the case for iron deficiency, which can have a number of effects on a person’s nails, including causing nails to become white or brittle, or develop a central groove or ridge, Podiatry Today revealed.

Iron deficiency is also the most common cause of koilonychia (aka spoon nails), a reverse curvature of the nails, causing them to become concave. However, other possible causes include autoimmune conditions (like lupus, celiac disease, and psoriasis), cardiovascular problems, vitamin B deficiency, and heavy exposure to petroleum-containing products, according to Medical News Today.

A 2017 paper published in the Journal of the American Academy of Dermatology noted that it isn’t always easy for a doctor to recognize koilonychia because the concavity of the nails may be very slight. The paper’s authors suggested using a simple "water-drop test" in which a drop of liquid is placed on the nail. If it remains in place rather than sliding off, this indicates that the nail is concave and an underlying condition like iron deficiency may be to blame.

Hair loss could be a sign of needing more iron

Although most people want a beautiful head of hair, hair is pretty superfluous — biologically speaking. Because it isn’t necessary for survival, our hair is low on the priority list when it comes to getting a share of the nutrients we consume, including iron. This can lead to problems with hair growth and can even cause your hair to fall out.

According to a paper published in Dermatology Practical & Conceptual in 2017, iron deficiency anemia is a well-documented cause of hair loss. It’s unclear, however, how exactly low iron damages hair. The authors pointed out that the hair matrix (the part of the follicle from which the hair shaft grows) contains some of the most rapidly dividing cells in the body. Iron is needed to make the enzymes that control DNA synthesis, so dividing cells need a lot of iron. Iron may also regulate certain genes in the hair follicle. It’s also unclear if simply having low ferritin (iron stores) without anemia is enough to cause hair loss and, if so, what level of ferritin is ideal to ensure hair health.

Pale skin can be a sign of iron deficiency

If you gaze in the mirror and feel you look more vampire than human, know that your pale skin could be a sign of low iron, according to Medical News Today. Blood gets its red color from red blood cells, which in turn get their hue from hemoglobin. When oxygen binds to the iron at the center of hemoglobin, the molecule becomes bright red. After delivering oxygen to cells, hemoglobin takes up carbon dioxide, which turns the molecule a darker red with a hint of purple. When you’re anemic, you have lower hemoglobin levels, which result in pale skin, especially in areas where blood vessels are close to the surface, such as the eyelids, gums, and fingers.

"Paleness in your inner eyelids is a telltale sign of anemia, regardless of race," Healthline explained. "It is also considered a sensitive indicator of severe anemia." However, simply having very fair skin is not automatically cause for alarm. "Paleness often occurs along with other symptoms, such as those associated with anemia," according to the site. So be sure to pay attention all of your body’s clues.

A swollen tongue and other mouth problems are frequently seen with iron deficiency

Having iron deficiency anemia (IDA) can cause a lot of mouth issues. In a 2014 study published in the Journal of the Formosan Medical Association, researchers examined the link between various oral complaints and IDA. Among subjects with IDA, 76 percent had a burning sensation in their mouth, while 56 percent had lingual varicosity (swollen veins in the tongue). In addition, about half had dry mouth, while one-third had oral lichen planus (chronic inflammation of the mouth’s mucus membranes), and more than a quarter had atrophic glossitis (an inflammatory condition in which the papillae on the tongue that contain the taste buds are destroyed, making the tongue look shiny and smooth).

According to a study published in the American Journal of Medical Science, the severity of iron deficiency directly correlates to the severity of mouth problems. Compared to those with iron deficiency, those with anemia had more painful areas on their tongue and a lower threshold for pain in these areas. They also produced less saliva. With iron supplements, however, pain decreased and pain threshold and saliva production increased.

Eating ice and other nonfood items may mean you need more iron in your diet

When your body is severely lacking in a particular nutrient, it may lead you to eat strange things in an attempt to get what it needs. Those with severe iron deficiency anemia may have pica, a condition in which individuals crave and eat nonfood items, according to an article published in the Journal of Medical Case Reports. Common examples include ice, clay, dirt, chalk, paint chips, and even cigarette butts.

Pica isn’t always associated with a nutritional deficiency, but pagophagia (eating ice) seems to be tied particularly closely to iron deficiency with or without anemia (via Mayo Clinic). It’s unclear why those low on iron crave ice. It may simply be that the cold ice increases alertness and helps combat the severe fatigue and mouth pain common in anemia. A 2010 study published in BMC Hematology examined 262 non-pregnant iron-deficient patients and found that 118 (45 percent) had pica. Of those, 87.3 percent craved and ate ice.

Depending on what’s eaten, pica can have potentially serious consequences. Although ice isn’t necessarily dangerous, other items may cause poisoning or introduce harmful bacteria or parasites. Items that can’t be digested can cause constipation and intestinal blockages, which may require surgery.