Scientists Say 2 Vitamin Deficiencies Commonly Cause Fatigue

If you’re feeling wiped out, it’s easy to chalk it up to your busy schedule or stress. But in some cases, it’s a sign that something’s amiss.

New research found that low levels of two vitamins—B12 and folate—are linked to a higher risk of chronic fatigue. The study, which was published in the journal Nutrients, had 602 healthy adults answer questions about their fatigue and motivation levels. The researchers also measured the participants’ blood levels of folate, vitamin B12, and homocysteine, a substance that tends to rise when folate and vitamin B12 are low.

The researchers confirmed that participants with higher levels of homocysteine typically had lower levels of folate and vitamin B12. But they also discovered that men with higher homocysteine levels were more likely to report having fatigue, while women were more likely to say that they felt less motivated when their levels were off.

According to dietitians, this association is worth exploring if you’re struggling with fatigue. Here’s why.

Meet the experts: Jessica Cording, M.S., R.D., registered dietitian and author of The Little Book of Game-Changers; Keri Gans, M.S., R.D., registered dietitian and author of The Small Change Diet.

Why are low B12 and folate levels linked with fatigue?

Vitamin B12 and folate (B9) are both water-soluble vitamins in the vitamin B complex. Vitamin B12 supports the function of the central nervous system and is needed for healthy red blood cell function, while folate is required for proper cell division, according to the National Institutes of Health (NIH).

“B12 and folate both help the body produce healthy red blood cells, which carry oxygen,” explains Keri Gans, M.S., R.D., registered dietitian and author of The Small Change Diet. “When levels are low, the body may not deliver oxygen as efficiently, leaving a person feeling tired, weak, or run down.”

Both of these vitamins “play a really big role in how our body turns food into fuel,” says Jessica Cording, M.S., R.D., registered dietitian and author of The Little Book of Game-Changers. “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.

How to tell if you’re low in these vitamins

“Feeling tired does not necessarily indicate a B12 or folate deficiency,” Gans cautions. Fatigue can be caused by a myriad of factors, not all of which are biological—but if it reaches a certain threshold, it’s worth looking into. “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.

Still, Cording recommends having a healthy suspicion that you may be low in B12 and folate if you’re feeling more tired than usual, struggling to focus, feeling a little down, or eating a diet that’s lower in those vitamins. “A blood test is the best way to know for sure,” she says.

How to add more B12 and folate to your diet

If you suspect—or know—that you’re low in vitamin B12 and folate, dietitians recommend trying to eat more foods that contain these nutrients.

“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 you should focus on your diet first. “Look at what you’re eating,” she says. “If you’re not getting these vitamins from regular food sources, consider adding them.”

If you’re really struggling with fatigue and a blood test confirms that your levels of these nutrients are low, Cording recommends taking a supplement. But consult with your healthcare provider first. Ask about how much of each supplement to take, and discuss any medications you may be on. “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 ingesting enough B12, but still not having optimal levels, she explains.

Ultimately, if you’re struggling with fatigue, it’s important to take action rather than hoping it will get better in time. “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.”