If you feel wiped out, it is easy to blame your schedule, stress or a rough night’s sleep. But persistent fatigue can sometimes signal that something else is going on.
New research has linked low levels of two vitamins, B12 and folate, with a higher risk of fatigue-related symptoms.
The study, published in Nutrients, looked at 602 healthy adults and assessed their fatigue and motivation levels. Researchers also measured blood levels of folate, vitamin B12 and homocysteine, a substance that tends to rise when folate and vitamin B12 are low.
They found that participants with higher homocysteine levels usually had lower folate and vitamin B12 levels. Men with higher homocysteine were more likely to report fatigue, while women with higher levels were more likely to report lower motivation.
The study does not prove that low B12 or folate caused fatigue. It found a link. Still, dietitians say the association is worth paying attention to if you feel unusually tired and cannot explain why.
Why are low B12 and folate levels linked with fatigue?
Vitamin B12 and folate, also known as vitamin B9, are both water-soluble B vitamins. They play important roles in red blood cell production, cell division, nervous system function and the way the body uses energy from food.
“B12 and folate both help the body produce healthy red blood cells, which carry oxygen,” explains registered dietitian Keri Gans. “When levels are low, the body may not deliver oxygen as efficiently, leaving a person feeling tired, weak, or run down.”
That oxygen connection matters. Red blood cells help move oxygen around the body, including to the brain and muscles. When B12 or folate levels are low, the body may not make red blood cells as effectively, which can contribute to fatigue, weakness and low stamina.
Both vitamins also support the body’s energy pathways.
“B12 and folate “play a really big role in how our body turns food into fuel,” says registered dietitian Jessica Cording. “If that process is not efficient because someone isn’t getting enough of the nutrients they need, it can definitely lead to fatigue,” she says.
Homocysteine may also be part of the picture. When B12 or folate levels are low, homocysteine can rise. Elevated homocysteine has been linked with oxidative stress and changes in blood vessel function, although more research is needed to understand exactly how that may relate to fatigue.
The practical takeaway is fatigue is not always solved by sleeping more or pushing through. If tiredness is persistent, unexplained, or paired with symptoms such as weakness, dizziness, numbness, tingling, shortness of breath, brain fog, low mood, heavy periods, gut symptoms, or a restricted diet, it is worth asking your GP whether blood tests could help.
How to tell if you’re low in these vitamins
“Feeling tired does not necessarily indicate a B12 or folate deficiency,” Gans says.
Fatigue can come from many things, including poor sleep, stress, heavy periods, low iron, thyroid issues, infection, mental health concerns, certain medicines, diet changes or simply doing too much for too long. Still, persistent fatigue is worth taking seriously.
“If fatigue is persistent, unexplained, interfering with daily life, or not improving with adequate sleep, nutrition, hydration, and stress management, it’s worth checking in with a healthcare provider,” Gans says.
Cording recommends keeping B12 and folate on the radar if you feel more tired than usual, struggle to focus, feel flat, or eat a diet that is lower in these vitamins. That can include vegan or mostly plant-based diets, very limited diets, or eating patterns with few fortified foods.
“A blood test is the best way to know for sure,” she says.
Your GP may check B12 and folate together, often alongside a full blood count, iron studies, thyroid function and other tests depending on your symptoms
How to add more B12 and folate to your diet
If you suspect, or know, that your B12 or folate levels are low, dietitians recommend looking at food first.
“B12 is found in fish, poultry, meat, eggs, dairy, and fortified foods, while folate is found in leafy greens, beans, lentils, asparagus, citrus fruits, avocado, and fortified grains,” Gans says.
Cording agrees that diet is the best place to start.
“Look at what you’re eating,” she says. “If you’re not getting these vitamins from regular food sources, consider adding them.”
For B12, that may mean adding more eggs, dairy, fish, chicken, lean meat, fortified plant milks, fortified cereals or nutritional yeast. For folate, try adding more leafy greens, legumes, asparagus, citrus, avocado and fortified grain foods.
If a blood test confirms low levels and fatigue is affecting daily life, a supplement may be helpful. Speak with your GP first, especially if you take regular medication, have gut issues, are pregnant, eat a vegan diet, or have had weight-loss surgery.
“Certain medications can deplete levels of some nutrients,” Cording says. “For example, if you’re regularly taking antacid medications, that can interfere with B12 absorption.”
In that case, you may be eating enough B12 but not absorbing it well. Some people may need a different supplement dose, ongoing monitoring, or in some cases, injections.
Ultimately, ongoing fatigue is not something to ignore.
“If you don’t feel right, talk to your healthcare provider and get a blood test,” Cording says. “This is more common than you think.”
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