A diet without enough iron, folic acid or vitamin B12 may lead to anemia, in which your blood does not carry enough oxygen to the rest of your body. Anemia from low iron may cause no symptoms while it is mild, and most of the time its symptoms start mild and develop slowly; they may include feeling weak or tired more often than usual, or with exercise. When you see your own doctor about the tiredness, the first blood test to name is the complete blood count.
How this differs from ordinary tiredness, and when to see your doctor
Ordinary tiredness can be a normal and important response to physical activity, emotional stress, boredom or lack of sleep. See your own doctor when tiredness is not relieved by enough sleep, good nutrition or a low-stress environment. Fatigue, a feeling of weariness, tiredness or lack of energy, is also different from drowsiness, which is feeling the need to sleep: fatigue is a lack of energy and motivation, so feeling drained without wanting a nap still counts. It is a common symptom and usually not due to a serious disease, though it can also point to a more serious mental or physical condition.
Fatigue has many possible causes, including anemia, iron deficiency without anemia, depression or grief, persistent pain, sleep disorders such as insomnia or obstructive sleep apnea, and a thyroid gland that is underactive or overactive. If your mood has been low as well, raise it at the same visit, and check how long a low mood can last before it needs an appointment of its own (see Flat and tired for weeks while eating less? Book a doctor's visit).
Medicines such as sedatives and antidepressants can cause fatigue too, and certain medicines may also cause drowsiness or fatigue, including antihistamines for allergies, blood pressure medicines, sleeping pills, steroids and diuretics, also called water pills. Do not stop or change any medicine without first talking to your own doctor or the provider who prescribed it, and ask whether it could be adding to the tiredness.
Contact your own doctor's office for an appointment when any of these applies to you:
- unexplained weakness or fatigue, especially with a fever, unintentional weight loss or regular sweats
- constipation, dry skin, weight gain, or being unable to tolerate cold
- waking up and falling back to sleep many times during the night
- frequent headaches
- taking medicines, prescribed or not, or using drugs that may cause fatigue or drowsiness
- feeling sad or depressed
- insomnia
Tell the doctor that you are eating less on purpose, and since when, so the weight you are losing is not mistaken for the unintentional kind that can come with unexplained fatigue.
Why iron or vitamin B12 can run low even when you eat carefully
Iron and vitamin B12 can run low even when you eat carefully, because careful food choices help with only one of the two steps: the food has to supply them, and your body has to absorb them. On the food side, your body gets vitamin B12 from foods such as meat, poultry, shellfish, eggs, fortified breakfast cereals and dairy products, and a lack of it may be due to dietary factors, including eating a strict vegetarian diet. You may not get enough iron in your diet if you are a strict vegetarian or do not eat enough foods that contain iron. Eating far less can mean eating less of the foods that supply both.
Absorption depends on your stomach and gut as well as on the food. Your body must absorb enough vitamin B12, and a protein called intrinsic factor, released by cells in the stomach, helps it do this efficiently. A well-balanced diet can help you get enough vitamin B12 from the foods you eat, but it cannot prevent anemia in people with health conditions that stop the body using vitamin B12 properly. Some health conditions, medicines and habits can make it difficult to absorb enough, including:
- pernicious anemia, in which the body destroys the stomach cells that make intrinsic factor
- surgery that removes certain parts of the stomach or small intestine, such as some weight-loss surgeries
- Crohn disease, celiac disease or other problems that make it difficult to digest foods
- alcohol use
- taking antacids and other heartburn medicines for a long period of time
- long-term use of the medicine metformin
Iron can fall short in the same two ways, and in two more. Your body may not absorb enough iron from your diet because of celiac disease, Crohn disease, gastric bypass surgery, or taking too many antacids or too much of the antibiotic tetracycline. Iron also runs low when you lose more blood cells and iron than your body can replace, or when your body needs more iron than normal, such as during pregnancy or breastfeeding.
Common causes of bleeding include heavy, long or frequent menstrual periods, peptic ulcer disease, and taking aspirin, ibuprofen or medicines that may thin the blood for a long time. Telling the doctor which of these apply to you helps them decide which tests to order; having one is not a diagnosis.
Vitamin B12 deficiency anemia may cause no symptoms, or only mild ones. When it does, they may include:
- diarrhea or constipation
- fatigue, lack of energy, or lightheadedness when standing up or with exertion
- loss of appetite
- pale skin
- feeling irritable
- shortness of breath, mostly during exercise
- a swollen, red tongue or bleeding gums
Over a long time, low B12 can damage nerves, with signs including numbness and tingling of the hands and feet, loss of balance and trouble concentrating. That damage may stay for good if you do not start treatment promptly after your symptoms begin, so name any of these signs to your own doctor's office when you phone to book the visit. Confusion and dizziness cannot wait for that visit: with this tiredness, either one means contacting your doctor right away. If you have almost no appetite, raise that at the same visit (see No appetite at all? Start by writing down one day of eating).
Which blood tests to ask for by name
Name the complete blood count first, then ask whether an iron level and a vitamin B12 level belong in the same blood draw; the doctor decides which to order. The complete blood count is one of the most common blood tests, often done as part of a routine checkup, and it measures many different parts of your blood. These are the results on it that may be a sign of anemia:
| Result | What it measures | What may be a sign of anemia |
|---|---|---|
| Red blood cells | The cells that carry oxygen from your lungs to the rest of your body | A level higher or lower than normal |
| Hemoglobin | The iron-rich protein in red blood cells that carries oxygen | A level higher or lower than normal |
| Hematocrit | How much space red blood cells take up in your blood | A level that is too low |
| Mean corpuscular volume | The average size of your red blood cells | A level higher or lower than normal |
Some normal ranges differ between men and women, and age, high altitude and race also may affect them, so ask your doctor whether your results are outside an acceptable range for your individual needs. Ask about an iron level even if the blood count looks normal, because iron deficiency without anemia is one of the possible causes of fatigue. A provider may also order other tests, including other measures of iron and tests that look for where blood may be lost, further vitamin B12 tests, and kidney, liver and thyroid function tests.
Hold off on iron or vitamin pills bought over the counter until you have talked to your doctor. Most of the time, a provider will measure your iron level before you start supplements, and you can ask them whether any supplemental vitamins might help you. If a B12 level comes back low, ask what is causing it, because the treatment depends on the cause.
A doctor looking for anemia may ask what you eat and whether other people in your family have been diagnosed with anemia, on top of the questions any visit for tiredness brings about your medical history, fatigue symptoms, and your lifestyle, habits and feelings. Have these answers ready too:
- when you started eating far less, and which foods you cut out
- every medicine and supplement you take
- any operation on your stomach or bowel
- if you have periods, whether they are heavy
Then ask in words like these: "I have been eating far less for three months, and by mid-afternoon I am exhausted in a way sleep does not fix. Could this be anemia, or low iron or vitamin B12, and can we check a complete blood count?"
Signs that need your doctor right away, an emergency room or 911
With thoughts of harming yourself or of suicide, dial 911 if it is an emergency; if it is not, get help right away by calling or texting the 988 Suicide & Crisis Lifeline at 988, and tell your own doctor too.
Tiredness that comes with any one of these other signs means contacting your own doctor right away, ahead of any booked appointment:
- confusion or dizziness
- blurred vision
- little or no urine output
- recent swelling and weight gain
Dizziness, and lightheadedness when you stand up, can both come from anemia itself, and with this tiredness either one still means contacting your doctor right away rather than waiting for a booked visit.
Bleeding is one of the ways iron runs low, and blood in your stool or a change in its color means contacting your doctor right away. If you vomit blood, you will need to be examined right away, by your doctor or at an emergency room. Iron pills can also turn stools black, and a provider can test the stool to check for blood, so when you get in touch, mention any iron you have started.
If NicoCares is where your weight care comes from, tell your care team promptly about this tiredness in Spruce, the app you already use to reach them, and send them the blood count once it is back. For any sign in this section, turn first to whichever that sign names above, whether it is 988, 911, an emergency room or your own doctor's office, because NicoCares does not run an emergency service; message the care team after that.
