If you have been dragging yourself through the day and chalking it up to age or stress, you are not alone. A lot of us have quietly accepted that kind of exhaustion as just the way things are now.
But three primary care doctors say that daily fatigue is not something you should simply live with. And more often than not, there is a specific, treatable reason behind it.
What Doctors Look For First
Dr. Alexander Acosta, MD, a primary care doctor with SonderCare, says that when a patient comes in feeling persistently tired, he does not jump to conclusions. He starts by asking about sleep, diet, and stress, all of which are closely tied to energy levels.
Dr. Michael Billington, MD, chief science officer at PrimaryMD, notes that certain symptoms require urgent attention. He says that unintentional weight loss, fever, night sweats, shortness of breath, chest pain, abnormal bleeding, or new lymph node swelling all need to be evaluated quickly.
Fortunately, he says, most cases of fatigue are not that serious. All three doctors agree on the next step: a basic blood test to check nutrient levels.
The Two Deficiencies Behind Most Fatigue
All three doctors named the same two culprits: low iron and low vitamin B12.
Dr. Alexa Mieses Malchuk, MD, MPH, FAAFP, a family practice physician at Geisinger, says that in the United States, iron, vitamin D, B12, folate, and magnesium are all common deficiencies. Iron and B12 shortfalls are especially common among people who eat mostly plant-based. Dr. Acosta adds that many people are low in iron, B12, and vitamin D all at the same time.
Here is why B12 matters so much. Dr. Acosta explains that B12 is needed to form red blood cells, which carry oxygen to every tissue in your body. When B12 is too low, oxygen delivery drops, and that can cause fatigue, brain fog, and muscle weakness. B12 also keeps the protective sheath around your nerves healthy. If levels stay low for a long time, the effects go beyond tiredness and begin to affect the nervous system.
A 2022 scientific article found that even B12 levels that are on the low end of normal can lead to fatigue and exhaustion. And research published in JAMA has also shown that iron deficiency can cause fatigue and trouble concentrating.
Why the Risk Goes Up After 50
This is where our generation needs to pay particular attention. Dr. Acosta says that beyond age 50, the body produces less stomach acid and fewer of the proteins needed to absorb B12 from food. That means even people who eat meat regularly can become deficient.
In those cases, he says, sublingual tablets, the kind that dissolve under your tongue, or B12 injections are more effective because the vitamin bypasses the gut entirely.
Dr. Billington also points out that certain common medications can affect B12 and iron levels. These include long-term metformin, proton pump inhibitors, H2 blockers, colchicine, cholestyramine, and oral contraceptives. People taking GLP-1 drugs are also at risk, he says, because appetite suppression can reduce nutrient intake overall.
Foods That Can Help
If your blood work shows a deficiency, the first place to look is your plate. Dr. Billington explains that vitamin B12 is made only by bacteria and reaches us almost entirely through animal foods.
He recommends eating more of these:
- Eggs
- Shellfish: clams, mussels, and oysters
- Oily fish: salmon, mackerel, and sardines
- Beef
For plant-based eaters, Dr. Billington says fortified foods are non-negotiable. That includes fortified breakfast cereals, fortified soy or almond milk, fortified meat substitutes, and fortified nutritional yeast. He notes that fermented foods like tempeh, miso, kimchi, and sauerkraut do not produce enough B12 to matter. And spirulina, often marketed as a B12 source, does not have enough of the nutrient to make a real difference.
To boost iron without eating meat, focus on dark leafy greens, beans, lentils, and tomatoes.
When Food Alone Is Not Enough
Dr. Acosta says that when levels are already low, diet alone may not bring them back up fast enough. That is where supplements can help.
Dr. Billington adds that some people cannot absorb B12 from food no matter how much they eat, including those who have had gastric bypass surgery or have certain autoimmune conditions. For them, dietary changes will not solve the problem on their own.
All three doctors say that people eating vegan or vegetarian diets should consider iron and B12 supplements if their bloodwork shows a deficiency. Dr. Malchuk reminds readers that these supplements are not regulated by the FDA, so it is important to choose ones that are third-party tested. That ensures the dose is accurate and there are no harmful ingredients.
One important note from Dr. Billington: if you are not actually deficient, taking a B12 supplement will not give you more energy. Supplements are for people who are truly low, not a general pick-me-up.
The Step Worth Taking Today
Dr. Acosta says that patients often normalize their fatigue for months or even years before getting tested. They assume it is stress or aging and never think to check their nutrient levels. But testing first matters, he says, because there may be other issues involved and supplementing without knowing could mask them.
If you have been tired for a while and cannot quite figure out why, a simple blood test may give you the answer. It is worth asking your doctor about at your next visit.
