We know to take our vitamin D in the winter and ramp up vitamin C when our immune system needs some love, and we never miss a day of our omega-3s. But there’s another nutrient many of us may need more of—and it’s finally making its way onto our radars, thanks to a little help from the attention of celebrities like Lo Bosworth, Chelsea Handler, and Rita Ora: vitamin B12.

We think of vitamin B12 as important for energy, and while it’s true that it helps us turn fat and protein into energy, it does so much more than that. “B12 is vital for the functioning of your nervous system, creating DNA and RNA (the building blocks of every cell in your body), brain health, and carrying oxygen throughout the body,” says Maggie Michalczyk R.D.N.

Like all vitamins, we can’t produce the B12 we need on our own, and have to get it through diet and/or supplements. (It’s found in animal products like eggs, milk, yogurt, cheese, shellfish, salmon, tuna, chicken, and beef.) And since B12 is a water-soluble vitamin and isn’t stored in our body long-term, we need to re-stock regularly.

Thing is, we’re apparently not too good at getting in that much-needed B12: The National Institutes of Health estimates that up to 15 percent of Americans are deficient. Some people—like vegetarians and vegans, who don’t eat many (or any) animal products, and those with digestive conditions, who often have trouble absorbing the vitamin—are at higher risk for deficiency, but vitamin B12 is important for everyone, explains Jonathan Valdez, R.D.N., owner of Genki Nutrition and spokesperson for the New York State Academy of Nutrition and Dietetics.

Vitamin B12 deficiency can cause some pretty crummy (and sneaky) side effects—and lead to serious health issues if left untreated. “Many people with deficiency go months or years without being diagnosed because it’s easy to write off the symptoms as stress from our go-go-go lifestyle,” says Michalczyk.

Below are nine signs you’re seriously wanting for B12 you shouldn’t overlook.

1. You’re Just Plain Exhausted

“Fatigue is one of the first signs of B12 deficiency,” says Michalczyk. Your body relies on the vitamin to make red blood cells, which carry oxygen to your organs. Without enough red blood cells to transport that oxygen, you can develop anemia, which is typically marked by fatigue (think overall weakness, trouble keeping up with your pup on walks or carrying groceries, and even lightheadedness.) If you’re experiencing constant fatigue for no clear reason, your doctor can first test your red blood cell count to confirm if you have anemia and then order further testing to determine if low B12 is the culprit.

2. Your Tongue Has Lost Its Texture

It’s not uncommon for people with B12 deficiency to lose ‘papillae,’ the tiny, taste bud-containing bumps on your tongue, says Pat Salber M.D., creator of the website The Doctor Weighs In. As a result, your tongue may appear smoother and shinier than usual, and your sense of taste may seem dull. For some people, vitamin B12 deficiency may also cause glossitis (inflammation of the tongue) and even mouth ulcers or burning and itching. These oral issues occur because vitamin B12-related anemia interferes with the proper growth and development of red blood cells.

3. You’re Pale Or Jaundiced

Because B12 influences red blood cell production and deficiency can leave you with a shortage, you may notice you look paler than usual, explains Valdez. Deficiency can also cause the red blood cells you do have to break down and release an orange-yellow pigment called bilirubin, which then leaves you looking rather yellow.

4. Your Hair Has Been Falling Out

Most of us lose an average of 80 strands of hair per day—and a lack of B12 can contribute to excess shedding. This, too, is because of B12’s role in red blood cell production and transport of oxygen throughout the body, says Valdez. Fewer blood cells and less oxygen to your hair follicles mean locks that are starving for nutrients.

Related: 8 Possible Reasons Why Your Hair Is Falling Out

5. You Feel A Tingling Sensation

“In conjunction with other B vitamins, B12 plays an important role in keeping your nervous system functioning properly,” says Michalczyk. Specifically, B12 plays a role in the production of a fatty substance called ‘myelin’ that surrounds and protects your nerves. Without ample B12, nerve cells are more susceptible to deterioration, which can lead to a ‘pins and needles’ sensation called ‘paresthesia’ in your hands and feet (like the feeling you get when you sit cross-legged for too long and your foot falls asleep). Ignoring this for too long can cause permanent damage to your nerves, Salber says.

6. You’ve Been Tripping A Lot

Because of its role in producing myelin and regulating the nervous system, a lack of B12 can cause the nerves in the spinal cord to atrophy over time, which can eventually diminish your sense of touch and affect your sense of where your body is in space (called ‘proprioception’), leaving you unsteady, says Valdez. These feelings of instability can be worsened by the dizziness that often comes along with low B12-related anemia.

Since frequent tripping or stumbling can also be related to heart conditions or low blood pressure, talk to your doc if you’ve been feeling unusually clumsy.

7. You’re Very Forgetful

The deterioration of that protective myelin in nerves throughout your brain can leave you feeling incredibly absent-minded. “Most people come in before the symptom gets this bad, but symptoms that mimic dementia can occur,” says Michalczyk. In fact, one study published in the journal Neurology linked vitamin B12 deficiency to age-related memory decline—and even brain shrinkage. The researchers found that vitamin B12-deficient older people had the smallest brains and lowest scores on tests meant to measure thinking, reasoning, and memory.

8. You’re Stressed Or Sad All The Time

You may not associate your mood with vitamins, but many nutrients—including vitamin B12—can have an effect on your sense of well-being. “B12 deficiency may impact the production of mood-regulating neurotransmitters like serotonin and dopamine,” says Valdez. These chemicals are often known as the ‘feel-good’ hormones, and their dysfunction has been implicated in mood issues like depression.

9. You Take Certain Prescription Drugs

Over time, some drugs, like metformin (which is commonly prescribed to people with type 2 diabetes), heartburn medications, oral contraceptives, antacids like proton-pump inhibitors (PPIs), and even aspirin may lead to a vitamin B12 deficiency, explains Valdez. “These medications can reduce stomach acid, which then reduces the amount of B12 the body is able to absorb,” he says. To avoid any potential issues, Valdez recommends always asking your doctor about whether nutrient deficiencies are a side effect of any medications you’re about to start long-term.

Getting Your B12 Back On Track

“The only way to identify a vitamin B12 deficiency is to have blood work done by your doctor,” says Michalczyk. From there, they may recommend you eat more animal-based foods, if possible, or start taking a supplement to up your intake. If supplementing, Valdez recommends looking for B12 in the form of methylcobalamin (or methyl-B12), which is easiest for our bodies to absorb, at whatever dose your doctor recommends.

If your deficiency is a result of an inability to properly absorb vitamin B12 (as is the case in celiac or Crohn’s disease or because of certain meds), then B12 shots, which deliver the vitamin straight into your blood stream, are a good option, says Michalczyk. Just know that you’ll need a prescription and have to take a trip to the doc’s office to get one.

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