B vitamins help keep your metabolism running properly, and they're especially important as you age. Image Credit: gilaxia/E+/GettyImages

Most of us probably think of vitamins as single nutrients, like vitamin C and vitamin D, but B vitamins are actually a group of eight different nutrients. Together, they're largely responsible for helping your metabolism function properly, much like how the engine in your car keeps it running.

B vitamins are in a class called water-soluble vitamins, which means your body doesn't store them. Instead, any surplus gets flushed out of your system. That's why it's especially important to get adequate amounts of each B vitamin through your diet — or supplements, if necessary — to make sure you do not develop a deficiency.

B1 Keeps the Lights On

Vitamin B1, or thiamine, is important to your overall metabolism, which refers to how the body uses energy, according to the National Institutes of Health (NIH). This means those who burn more energy have an increased need for thiamine. The nutrient also helps with nerve and muscle function.

Someone with a slight thiamine deficiency may experience headaches or fatigue and be irritable. Those with a major deficiency may show signs of a condition called Beri Beri, characterized by muscle weakness, loss of coordination, pain, mental disorientation and possible paralysis.

Most Americans get enough thiamine every day in the form of whole and enriched grains, pork, legumes, seeds and nuts. Keep in mind that the nutrient is heat-sensitive, though. When cooking meat, up to 60 percent of its B vitamins can be lost at high temperatures, when the juices run off. But consuming these juices can help you get the full B benefit of the food, according to the U.S. Department of Agriculture.

Those who may benefit from taking a thiamine supplement include chronic alcohol abusers, those undergoing dialysis treatment, people who have HIV/AIDS and those with anorexia.

Read more: The Side Effects of Thiamine Mononitrate

B2 Tells Your Cells to Release Energy

Riboflavin (aka vitamin B2), like thiamine, is responsible for energy release in every single cell of the body. In the U.S., much of our riboflavin comes from milk. However, UV light destroys riboflavin, so look for milk in opaque containers. If you don't eat dairy, you can get your B2 from broccoli, dark leafy greens, fish, poultry and eggs.

Those who don't get enough riboflavin can develop a condition called ariboflavinosis, according to the NIH. Symptoms include cracks on the corners of your mouth and a swollen tongue and lips. You may also develop greasy scales on your skin, usually near the nose, ears and mouth.

If you are deficient in riboflavin, you are usually deficient in many other vitamins as well. If you have congenital heart disease, chronic alcoholism, anorexia or some cancers, you may want to speak with your doctor about supplementation.

Read more: 5 Common Vitamin Deficiencies Linked to Chapped Lips

B3 Maintains Metabolism

Niacin, or vitamin B3, is also important to ensuring your metabolism is in working order, according to the NIH. If you get enough protein in your diet, you probably have enough niacin. That's because you can get niacin on its own, but your body can also make it from tryptophan, an amino acid (one of the building blocks of protein). You can also get niacin from enriched grains, legumes, milk, coffee and tea.

If you don't get enough niacin, you may come down with a disturbing condition called pellagra, which is characterized by diarrhea, dementia and dermatitis.

Even though niacin is water-soluble like the other B vitamins, there have been reports of overdose, which creates a temporary flushing effect in the body.

B5 Breaks Down Macronutrients

Pantothenic acid, also known as vitamin B5, works in the body to help you metabolize carbohydrates, fat and protein. The National Institutes of Health suggest that almost all plant and animal foods have some pantothenic acid, with the largest amounts appearing in shiitake mushrooms, tuna, chicken breast, avocado and sunflower seeds. Fortified foods can also give you 100 percent of most B vitamins, including pantothenic acid.

The wide availability of food sources of pantothenic acid makes deficiency extremely rare, appearing only in cases of severe malnutrition. In those cases, one would experience numbness in the hands and feet, headache, fatigue, irritability and gastrointestinal issues.

Extremely high intake of pantothenic acid from supplements can result in diarrhea or water retention.

B6 Helps You Better Absorb Protein

You need vitamin B6, or pyroxidine, for amino acid metabolism. This is how protein from the food you eat gets broken down into amino acids, which your body then uses to make cells, muscles and other tissue. B6 also aids in the formation of an iron-containing compound called heme, which gives your blood the ability to carry oxygen. You also need this B nutrient to help convert tryptophan to niacin, which is just one example of how B vitamins work together to keep you healthy.

You get B6 in your diet from chicken, pork, legumes, fish, eggs and some cereals. If you don't get enough of the vitamin, you could be weak, have skin inflammation and suffer poor nerve function.

High doses of pyridoxine given over long periods of time may result in painful neurological symptoms known as sensory neuropathy.

Read more: Vitamin B6 Toxicity Symptoms

Brown rice is a good source of B-complex vitamins Image Credit: fcafotodigital/iStock/GettyImages

B9 Plays a Key Role in a Healthy Pregnancy

If you've ever been pregnant, you're likely familiar with B9, which is better known as folate or folic acid. What's with the two names? Well, folate refers to the B vitamin that occurs naturally in food, and folic acid is the synthetic form found in supplements, according to the NIH. However you get it, this nutrient is important for the metabolism of protein and in keeping your blood healthy. During pregnancy, it's also essential in forming the fetus' neural tube, from which the brain and spinal cord develop.

Pregnant women who are deficient in folate run the risk of having babies born with defects that affect the head and spine, such as spina bifida or anencephaly. For others, folate deficiency can also cause poor growth, gingivitis, diarrhea, loss of appetite, forgetfulness and irritability. Low levels of folate are fairly common, according to Mount Sinai. Risk factors for deficiency include alcoholism, inflammatory bowel disease and celiac disease.

Folate is found in many foods, with the highest amount in liver, spinach, asparagus and Brussels sprouts. Other reliable sources of folate include broccoli, oranges, rice and peas.

Supplementing with too much folic acid may cause impairment of the immune system or anemia.

Read more: Fruits and Vegetables Containing Folic Acid

B12 Helps Your Body Use Fat and Protein

Vitamin B12, also known as cobalamin, is important in your body's protein and lipid metabolism, and in the synthesis of hemoglobin, according to the NIH. B12 helps make and maintain the outer covering of nerve fibers. Animal-derived foods are the main source of B12 in the diet, so deficiency is usually not an issue for omnivores. Vegans should take a supplement if they are not getting enough B12 from fortified foods or nutritional yeast.

A B12 deficiency can cause anemia or certain neurological issues, and it may even affect cognition by reducing the brain's total volume, according to a July 2019 study published in Neurology. A lack of vitamin B12 was associated with poorer long-term memory and perceptual speed, the researchers found.

To absorb B12, you must produce a protein called intrinsic factor in your stomach, which most people do. In rare cases, some people do not produce intrinsic factor and would experience deficiency symptoms. In addition, production of intrinsic factor decreases as you age, so getting your B12 levels checked as you enter middle age and beyond isn't a bad idea. Unless directed by a doctor or health care professional, there's no need for most people to seek a supplement, but toxicity is usually not an issue.

Biotin Makes Brain Food

Biotin, another important B vitamin sometimes referred to as vitamin H, is important for lipid and protein metabolism, and aids in gluconeogenesis, a metabolic activity that results in the formation of glucose, which your body — especially your brain — uses for energy. One cool fact about biotin is that the good bacteria in our gut can produce this nutrient. However, how much is produced varies from person to person, so it's still an essential vitamin to get from your diet.

You can get biotin from such foods as peanut butter, egg yolks and yeast. Biotin deficiency is extremely rare. According to Oregon State University, deficiency symptoms include hair loss, skin rash and depression. Consuming large amounts of raw egg whites can cause a biotin deficiency because a substance in the whites, called avidin, binds with the biotin and doesn't allow the body to absorb it. Cooking the egg destroys the avidin. There is no toxicity associated with biotin.

Do I Need a B Vitamin Supplement?

People take B vitamin supplements for various reasons. There is some evidence to suggest that B vitamin supplementation may help reduce the symptoms of stress and anxiety, according to a review published in Nutrients in February 2016. This type of supplementation is dependent on many factors, such as dose, current levels in the body and severity of symptoms, and should only be taken under a doctor's supervision.

Michigan Medicine notes that B complex may be helpful for canker sores, as deficiency is often found in people with recurrent canker sores. In addition, B vitamins, especially thiamin and pantothenic acid, may be helpful for wound healing.

As for other benefits, there is little or no scientific evidence to support that B-complex supplements help with acne, osteoporosis, PMS, indigestion, heartburn or a host of other conditions it is sometimes claimed to treat.