BY LAUREN BEDOSKY from Woman's Health Magazin

There's no overselling vitamin B12: It's basically essential for everything your body does.

Dubbed the “energy vitamin,” it promotes healthy nerve function, plays a major role in the production of DNA, and helps to keep your body filled with the red blood cells that carry oxygen throughout your body.

However, this critical vitamin is only available in food and supplements. Meats, dairy, and fortified grains are among the best sources, so, if you're vegetarian, vegan, or gluten-free, you may be unwittingly upping your risk of vitamin B12 deficiency, says Patricia Salber, M.D., board-certified internist and CEO of The Doctor Weighs In, a healthcare content company. Meanwhile, people with diagnosed pernicious anemia or atrophic gastritis can actually have problems effectively absorbing the vitamin.

Read more on how to eat healthy and still keep your shape.

That explains why up to 15 percent of Americans are vitamin B12 deficient, according to the National Institutes of Health. And that can bring about some pretty nasty symptoms (more on those later). Often, these symptoms take a long time to show up. After all, the body hangs onto any excess intake of B12. So if you suddenly cut it out of your diet, it can take three to four years to notice any B12 deficiency signs, explains Michael Roizen, M.D., chief wellness officer at the Cleveland Clinic Wellness Institute.

However, when they do show up, they show up strong. Problem is, they can easily be explained away by an exhausting sleep schedule, long hours at the office, as well as other neurological conditions such as nerve damage. Which is why it's so important to understand B12 deficiency signs and talk to your doctor if you spot any (or all) of them. (Don't worry, your doc will be able to help you easily get your levels back on track, through dietary changes, supplements, or B12 shots.)

Here, experts explain the top vitamin B12 deficiency symptoms every woman needs to know about:

According to Roizen, one of the early vitamin B12 deficiency symptoms includes tiredness. That's because, when your supply of B12 runs low, your body isn’t able to produce the red blood cells needed to deliver oxygen throughout your body. The result? Anemia.

This can cause you to feel unusually weak and run-down. Trouble is, tiredness is such a vague, general symptom that could easily be attributed to other causes (stress, lack of sleep). If the fatigue keeps getting worse and you can’t pinpoint an obvious cause, visit your doc, Salber says. First, your doctor will get a red-blood cell count to see if you have anemia. If you do, your doctor will order a blood test to check your B12 levels (among other nutrients).

Running from your brain and along your spinal cord all the way to your hands and feet, there's a long nerve tract called the posterior tract, which is coated in a fatty white substance known as myelin. Myelin not only insulates and protects the nerves, but it also speeds up the nerve impulses, making it possible for your hands and feet to sense touch, Roizen says.

Thing is, you need B12 in order to produce myelin. So, when you run low on this essential vitamin, your myelin breaks down and nerve impulses can’t travel as fast, he explains. The result? Tingling sensations in your hands and feet. See your doc if you get the prickles.

Just as a breakdown of myelin in your posterior tract can cause you to lose your sense of touch, it can also affect your proprioception, or your sense of where you are in space. “Proprioception is key for your balance,” Roizen says. “So if you cut out your proprioception, you have a tendency to fall.”

Unless you’re wearing sky-high stiletto shoes, falling or teetering around is definitely not normal. If you often lose your balance, make an appointment for a blood test.

That protective white substance known as myelin coats the nerve cells in your brain, which can leave you feeling more forgetful than usual if it deteriorates, Roizen says.

Sure, occasionally misplacing your phone or blanking on a co-worker’s name is no big deal, but if you find you’re increasingly off your game, take it seriously and get yourself tested. If you don't, your vitamin B12 deficiency symptoms can mimic dementia in just a year’s time.

Feeling unusually down lately? If there are no obvious reasons why (think: bad breakup, fewer daylight hours, family drama), low B12 levels may be to blame. One thought as to why this occurs is that B12 plays a key role in brain function and myelin production, Roizen says. In some people, a breakdown in myelin production presents as depression.

Basically, play it safe and get checked by your doctor.