Several vitamins and minerals play direct roles in how your body produces energy, and running low on any of them can leave you feeling persistently tired. The most common nutritional causes of fatigue are low iron, vitamin B12, vitamin D, and magnesium. If your tiredness doesn’t improve with better sleep and stress management, a nutrient gap is worth investigating.
Iron: The Most Common Nutritional Cause of Fatigue
Iron is essential for making hemoglobin, the protein in red blood cells that carries oxygen to every tissue in your body. When iron stores drop, your cells get less oxygen, and the result is a heavy, persistent exhaustion that sleep doesn’t fix. Low iron is one of the most widespread deficiencies worldwide, and it disproportionately affects women of reproductive age, pregnant women, and people who follow plant-based diets.
Beyond fatigue, low iron often shows up as pale skin, dizziness, shortness of breath, and a fast heartbeat. These physical signs can help distinguish iron-related tiredness from ordinary exhaustion caused by poor sleep or stress. The recommended daily intake for adult women ages 19 to 50 is 18 mg, while adult men need about 8 mg. During pregnancy, that jumps to 27 mg.
What you eat alongside iron matters. Calcium, tannins in tea and wine, and dairy products can all interfere with absorption of plant-based (non-heme) iron. Spacing these foods about one to two hours away from iron-rich meals makes a noticeable difference. On the flip side, pairing iron-rich foods with vitamin C helps your body absorb more of it. A simple example: squeeze lemon over a spinach salad or eat an orange with a bowl of fortified cereal.
Vitamin B12 and Energy Production
Vitamin B12 is a key player in how your cells generate energy. Inside your mitochondria, B12 acts as a cofactor for an enzyme that converts a compound called methylmalonyl-CoA into succinyl-CoA, which feeds directly into the Krebs cycle, your body’s central energy-producing pathway. Without enough B12, this process slows down, and fatigue is one of the earliest symptoms.
B12 deficiency can also affect your nervous system. One telling sign is trouble with balance or coordination, which happens when your nerves can’t send signals about body position as efficiently. If you’re tired and also feeling unsteady or experiencing tingling in your hands and feet, B12 is worth checking. Adults need 2.4 mcg per day, a small amount that most people get from animal products like meat, fish, eggs, and dairy. Vegans, older adults (who absorb B12 less efficiently from food), and people taking certain acid-reducing medications are at higher risk of deficiency.
Vitamin D and Persistent Low Energy
Vitamin D deficiency is remarkably common, especially in people who spend most of their time indoors or live in northern latitudes with limited sun exposure. Fatigue is one of its hallmark symptoms, alongside muscle weakness, cramps, and low mood. The connection between low vitamin D and tiredness is well established, though it can be easy to overlook because the symptoms creep in gradually.
The recommended daily intake for most adults is 600 IU, rising to 800 IU after age 70. Your body produces vitamin D when your skin is exposed to sunlight, but in practice many people don’t get enough this way, particularly during winter months. Fatty fish, fortified milk, and egg yolks provide some, but supplementation is often necessary to reach adequate levels. A simple blood test can tell you where you stand.
Magnesium and Muscle Fatigue
Magnesium is involved in over 300 enzymatic reactions in your body, including energy production, oxygen absorption, and electrolyte balance. When levels are low, you may feel physically drained, experience muscle cramps, or notice that exercise feels harder than it should. Magnesium deficiency is surprisingly common because modern diets often fall short of magnesium-rich foods like leafy greens, nuts, seeds, and whole grains.
If you’re considering a supplement, you’ll encounter different forms. Magnesium citrate is one of the more well-absorbed options and has been studied in the context of pain and fatigue. In one study of 80 women with fibromyalgia, 300 mg of magnesium citrate daily for eight weeks significantly reduced symptoms including tender points and fatigue compared to a control group. Magnesium malate, which combines magnesium with malic acid (a compound involved in your cells’ energy cycle), is another popular choice for people dealing with tiredness, though direct head-to-head comparisons between forms specifically for fatigue are limited.
Vitamin C and Stress-Related Exhaustion
Vitamin C does more for energy than most people realize. Your adrenal glands, which produce the stress hormone cortisol, contain some of the highest concentrations of vitamin C in your body. The vitamin serves as a cofactor for the enzymes that synthesize cortisol, but it also acts as a brake on the stress response, helping to prevent excessive cortisol release. When vitamin C is low, cortisol levels can stay elevated, which over time contributes to the kind of wired-but-exhausted feeling that comes with chronic stress.
Severe vitamin C deficiency (scurvy) causes pronounced fatigue, though you don’t need to be anywhere near scurvy to feel the effects. If your diet is low in fruits and vegetables, even a modest shortfall can contribute to low energy. Citrus fruits, bell peppers, strawberries, and broccoli are all rich sources.
B Vitamins Beyond B12
While B12 gets the most attention, other B vitamins also contribute to energy metabolism and can cause fatigue when they’re lacking. Deficiencies in B6, B9 (folate), and B12 can all lead to anemia, where your body doesn’t produce enough healthy red blood cells to carry oxygen efficiently. The result feels similar regardless of which vitamin is low: persistent tiredness, weakness, and sometimes brain fog.
Most people eating a varied diet get enough of these nutrients, but certain groups are at higher risk. Folate needs increase during pregnancy (which is why prenatal vitamins contain it), and some medications can deplete B6 over time. If you suspect a deficiency, a blood panel can check levels of individual B vitamins rather than guessing with a broad supplement.
How to Tell if Tiredness Is a Vitamin Issue
Not all fatigue comes from a nutrient gap, and it’s worth knowing what clues point toward a deficiency versus simple exhaustion from stress or sleep deprivation. Vitamin-related fatigue tends to persist even when you’re getting adequate rest. It often comes with other physical signs: pale skin and dizziness (iron), balance problems or tingling (B12), muscle weakness and low mood (vitamin D), increased hunger or unusual food cravings (sometimes called “hidden hunger”), or changes to your skin, hair, and nails (various B vitamins and vitamin A).
If your fatigue is new and you can trace it to a period of poor sleep, high stress, or overwork, lifestyle changes are the most logical first step. But if tiredness has become your baseline, especially if you notice any of those accompanying symptoms, blood work is the most efficient path forward. Testing for ferritin (iron stores), B12, folate, vitamin D, and magnesium covers the most common nutritional causes of fatigue and gives you a clear picture of what, if anything, to supplement.
Absorption Matters as Much as Intake
Taking a supplement or eating the right foods doesn’t help much if your body can’t absorb the nutrients properly. Beyond the calcium and tannin interference with iron mentioned earlier, several other factors affect absorption. Stomach acid is critical for B12 absorption, which is why people on long-term acid-reducing medications and older adults (who naturally produce less stomach acid) are prone to B12 deficiency even with adequate dietary intake. Gut conditions like celiac disease and Crohn’s disease can impair absorption of multiple nutrients at once.
Timing and pairing also make a difference. Fat-soluble vitamins like D absorb better when taken with a meal that contains some fat. Iron supplements are best taken on an empty stomach or with vitamin C, and away from coffee, tea, and calcium-rich foods. These small adjustments can meaningfully change how much of a supplement actually reaches your bloodstream.