Vitamin B-12 is necessary for a healthy nervous system and healthy blood cells. The best way to get vitamin B-12 is through your diet. This important vitamin is found in meat, fish, poultry, and dairy products. If you don’t eat enough of these foods, it could leave you with a deficiency.

There are other ways to develop a deficiency. For example, having diabetes mellitus can increase your risk of having a B-12 deficiency because it may be a side effect of metformin, a common treatment for type 2 diabetes mellitus. A 2009 study found that 22 percent of people with type 2 diabetes were low in B-12. The study results suggest metformin contributed to the deficiency.

Read on to learn the symptoms of B-12 deficiency, what it could mean for your overall health, and what you can do about it.

Symptoms of vitamin B-12 deficiency may be mild at first and not always obvious. If you’re slightly low on B-12, you may not have any symptoms at all. Some of the more common early symptoms are:

It may be easy to dismiss these as minor complaints. However, over time, insufficient B-12 can lead to bigger problems.

B-12 is mostly found in animal products. It doesn’t occur naturally in plants.

As a result, people who don’t eat meat or dairy products, such as vegetarians and vegans, may be at risk of B-12 deficiency. Some vegetarian foods, including breakfast cereals and energy bars, may be fortified with B-12.

Consuming enough vitamin B-12 isn’t the only problem. Your body also needs to be able to absorb it efficiently.

Certain medications may make it harder for your body to absorb B-12, including:

Another cause of vitamin B-12 deficiency is undersupply of instrinsic factor (IF), a protein created by stomach cells. These stomach cells can be vulnerable to attack by the immune system, and that can create a drop-off in IF production. IF is required to absorb dietary vitamin B-12 into the small intestine.

Very low levels of vitamin B-12 can result in serious complications, including anemia.

Anemia means you don’t have enough healthy red blood cells (RBCs). Because red blood cells are needed to carry oxygen in the bloodstream, anemia deprives your cells of much-needed oxygen.

According to a 2015 study in the Journal of Oral Pathology Medicine, less than 20 percent of those in the study who had vitamin B-12 deficiency also experienced pernicious anemia, a type of anemia specific to those with B-12 deficiencies.

Symptoms of anemia include:

Another possible symptom of a B-12 deficiency is losing your sense of taste and smell. More serious symptoms include fast or irregular heartbeat and shortness of breath.

B-12 deficiency can also lead to peripheral neuropathy with symptoms that may include numbness, weakness, pain, and paresthesia (a burning or itchy sensation of the skin). It’s usually felt on the arms, hands, legs, and feet. Some people experience numbness, tingling, or a prickly feeling.

Low B-12 tends to be associated with high levels of an amino acid called homocysteine. This can increase your risk of heart disease and stroke.

A severe, long-term B-12 deficiency can cause:

One of the potential complications of diabetes mellitus is neuropathy, also called nerve damage. It’s caused by the adverse effects of high blood glucose over a long period.

The most common symptoms of diabetic neuropathy are those described above for peripheral neuropathy that often affect arms, hands, legs, and feet.

Diabetic neuropathy can also affect other body parts, including the gastrointestinal (GI) tract.

You don’t have to have diabetes to develop neuropathy. Prolonged B-12 deficiency can also damage your nerves.

Whether you have diabetes or not, symptoms of neuropathy should not be ignored.

If you have symptoms of B-12 deficiency, see your doctor right away. Some of the symptoms, especially early on, can be vague. They can also be caused by a variety of other things.

A simple blood test can determine if the problem is low B-12. If you have diabetes and/or B-12 deficiency, your doctor will want to perform a complete history and physical examination to fully evaluate you.

Your blood glucose levels will also be taken into account in regard to diabetes mellitus.

Recommended levels of B-12 vary by age. Most teens and adults need 2.4 micrograms (mcg) per day. Children need between 0.4 and 1.8 mcg each day, depending on their age.

Maintaining healthy blood sugar levels may help you control B-12 absorption. In addition to diet, regular exercise and adequate sleep can often help. Your doctor can recommend a treatment plan tailored to your needs.

You may be advised to increase B-12 in your diet. Good sources of vitamin B-12 include:

Foods that may be fortified with B-12 include:

Be sure to read nutrition labels carefully.

Your doctor may also advise you to take oral vitamin B-12 supplements, especially if you have a vegetarian or vegan diet. If you’re severely deficient, they can give you B-12 injections.

Follow your doctor’s advice to avoid serious complications of B-12 deficiency. Also arrange for follow-up testing to make sure you’re on the right track.