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Testing B Vitamin Levels: What You Need to Know

Medically reviewed by 
Jessica Christie
Testing B Vitamin Levels: What You Need to Know

B vitamins are a group of 8 water-soluble vitamins that play vital roles in human metabolism. They are essential for the normal functioning of the nervous system, and they help the body convert food into energy. B vitamins also help to maintain healthy skin, hair, eyes, and liver. They aid in producing hormones and red blood cells and assist the body's use of carbohydrates, proteins, and fats. B vitamins are found naturally in various foods, including meat, poultry, fish, eggs, dairy products, legumes, and whole grains.

The body can't store most B vitamins well, so they must be consumed daily to keep up with our body's needs. People with reduced food intake or malabsorption issues may need to pay attention and test their B vitamin levels during wellness checkups. Luckily, most B vitamin levels can be restored through a healthy balanced diet and supplementation.


What are B Vitamins' Role in The Body?

These are the main roles of B Vitamins in the body and the consequences of their deficiencies:

Vitamin B1 (Thiamin)

Role: Thiamin, also known as Vitamin B1, plays a crucial role in cell growth and function. The small intestine absorbs it through active transport at normal doses and passive diffusion at higher doses. The human body stores limited amounts of thiamin, primarily in the liver, so it is important to have a continuous supply from the diet. Approximately 80% of the thiamin in adults is present as thiamin diphosphate (TDP), a cofactor for enzymes involved in amino acid, glucose, and lipid metabolism.

Deficiency: In the US, a lack of thiamin is uncommon as most individuals obtain the recommended daily intake through their diet. Nevertheless, a deficiency can arise from inadequate consumption of thiamin-rich foods, poor absorption in the digestive system, or increased elimination via urine, such as with alcohol abuse or certain medications like diuretics. Mild to moderate deficiency symptoms include weight loss, confusion, memory loss, muscle weakness, peripheral neuropathy, and decreased immunity.

Severe thiamin deficiency can lead to beriberi, resulting in muscle wasting and decreased sensation in the extremities. Beriberi can also lead to life-threatening fluid buildup in the heart and legs by impairing reflexes and motor function. Another outcome of significant thiamin deficiency, often seen with alcohol abuse, is Wernicke-Korsakoff syndrome, characterized by confusion, instability, and peripheral neuropathy. Both forms of deficiency can also occur in individuals with gastrointestinal issues such as celiac disease, those who have undergone bariatric surgery, or those with HIV/AIDs.  

Vitamin B2 (Riboflavin)

Role: Riboflavin, also known as Vitamin B2, is essential for the functioning of two coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzymes play crucial roles in energy production, cellular growth, metabolism of fats, drugs, and steroids, and in the conversion of other vitamins. Riboflavin is mainly absorbed in the small intestine, but the body can only store small amounts, so any excess is excreted in the urine.

Deficiency: Riboflavin deficiency is uncommon in the United States. Its causes can include inadequate intake, endocrine disorders (such as low levels of thyroid hormones), and certain diseases. The symptoms of riboflavin deficiency include skin problems, red and swollen mouth and throat, sores at the corners of the mouth, swollen and cracked lips, hair loss, reproductive issues, sore throat, itchy and red eyes, and damage to the liver and nervous system. Severe riboflavin deficiency can also impact the metabolism of other B vitamins and other nutrients due to decreased flavin coenzymes. If riboflavin deficiency is prolonged and severe, it can lead to anemia and cataracts.

Vitamin B3 (Niacin)

Role: Niacin, also known as Vitamin B3, is converted in the body to Nicotinamide Adenine Dinucleotide (NAD) and Nicotinamide Adenine Dinucleotide Phosphate (NADP). Over 400 enzymes require both molecules for metabolic reactions in the body. NAD is involved in reactions that transfer energy from carbohydrates, fats, and proteins to ATP, our body's primary fuel source. NADP assists with reactions such as synthesizing cholesterol and fatty acids and maintaining cellular antioxidant function. Niacin is absorbed mainly in the small intestine, but some of it gets absorbed in the stomach.

Deficiency: Pellagra is a disease caused by severe niacin deficiency. It manifests as skin discoloration, a rough texture, and changes in the digestive system. The condition can also cause depression, memory loss, fatigue, and even aggressive and paranoid behaviors.

Vitamin B5 (Pantothenic Acid)

Role: Pantothenic acid, also known as Vitamin B5, is crucial for the production of coenzyme A (CoA) and the acyl carrier protein, which are essential for fatty acid synthesis, and various other metabolic processes. Pantothenic acid can be found in plant and animal foods, mostly as CoA or phosphopantetheine. It is absorbed in the intestine and delivered to the bloodstream by active transport or simple diffusion. The body's intestinal flora also produces pantothenic acid, but it's unknown how much of this actually absorbs and contributes to bodily functions. Pantothenic acid is carried by red blood cells throughout the body and is primarily found in tissues as CoA, with smaller amounts as acyl carrier protein or free pantothenic acid.

Deficiency: A deficiency of pantothenic acid is rare as it is found in almost all foods except in cases of severe malnutrition. Determining pantothenic acid deficiency is challenging as it often occurs with deficits in other nutrients, making this deficiency hard to pinpoint.

Vitamin B6 (Pyridoxine)

Role: Vitamin B6, also known as Pyridoxine plays a vital role in over 100 enzyme reactions, mainly related to the metabolism of protein, carbohydrates, and lipids. Vitamin B6 helps with cognitive development by synthesizing neurotransmitters and regulating homocysteine levels in the blood. It also affects gluconeogenesis, glycogenolysis, immune function (boosting lymphocyte and interleukin-2 production), and hemoglobin formation.

Deficiency: Vitamin B6 deficiency is rare on its own and is often accompanied by low levels of other B vitamins, like B12 and folic acid. As the deficiency progresses, the symptoms become more noticeable. Symptoms of vitamin B6 deficiency include anemia, EEG abnormalities, dermatitis with cheilosis and glossitis, depression, confusion, weakened immunity, and in infants, irritability, acute hearing, and convulsions. Vitamin B6 deficiency can also result from kidney diseases, malabsorption syndromes, certain genetic disorders, and the long-term use of certain medications like antiepileptic drugs.

Vitamin B7 (Biotin)

Role: Biotin is a necessary nutrient found in some foods and can be taken as a supplement. It helps with the metabolism of fatty acids, glucose, amino acids, gene regulation, and cell signaling by acting as a cofactor for five carboxylases. Most biotin in food is bound to proteins, but it is released and absorbed by the small intestine after being processed by biotinidase enzymes.

Deficiency: Biotin deficiency is rare, and there has never been a report of severe biotin deficiency in individuals with a healthy diet. Symptoms of biotin deficiency can develop slowly and include hair loss, a rash around the eyes, nose, mouth, and perineum, conjunctivitis, aciduria, seizures, skin infections, brittle nails, and neurological issues such as depression and paresthesia. In infants, biotin deficiency can cause hypotonia (decreased muscle tone), lethargy, and developmental delays. The rash and facial appearance associated with biotin deficiency are referred to as "biotin deficiency facies."

Vitamin B9 (Folate)

Role: Folate is an important B vitamin found in various food sources. It plays a crucial role in creating DNA and cell division in the body. Additionally, a synthetic form of folate called folic acid is commonly used in fortified foods and dietary supplements.

Deficiency: Although folate deficiency is uncommon in the US, some individuals still don't consume enough of it. This lack of folate can lead to megaloblastic anemia. This blood disorder results in weakness, fatigue, trouble focusing, irritability, headache, heart palpitations, shortness of breath, and sores on the tongue or inside the mouth. In addition, the skin, hair, and fingernails may also change color. Furthermore, women with low folate levels are at a higher risk of giving birth to babies with neural defects like spina bifida and have a higher probability of delivering premature or low birth weight infants.

Vitamin B12 (Cobalamin)

Role: Vitamin B12 plays a vital role in maintaining the health of your blood and nerve cells and in the production of DNA, the genetic material in your cells. It also helps prevent megaloblastic anemia, a blood condition that results in feelings of fatigue and weakness.

Deficiency: Since the body stores an ample supply of vitamin B12, the deficiency symptoms may take years to surface. These symptoms include fatigue, weakness, pale skin, heart palpitations, loss of appetite, weight loss, infertility, numbness or tingling in hands and feet (a sign of nerve damage), balance problems, depression, confusion, dementia, poor memory, and mouth or tongue soreness. Vitamin B12 has also been associated with chronic pain and fibromyalgia. Infants may display signs of deficiency, such as failure to thrive, developmental delays, and megaloblastic anemia. It is crucial to promptly address a vitamin B12 deficiency, even in individuals who do not present with megaloblastic anemia, as it can harm the nervous system.

A lack of B vitamins, in general, has been linked to various symptoms. For example, brain function symptoms often arise, such as depression, anxiety, brain fog, stress, and sleep disturbances when B vitamin intake is insufficient. Also, those with certain conditions tend to have B vitamin deficiencies, such as in Polycystic Ovary Syndrome (PCOS).

How to Test B Vitamin Levels

A routine blood test called a Complete Blood Count (CBC) can detect various types of anemias. Macrocytic Anemia can result from deficiencies in vitamin B12 and/or folate, making this test useful for evaluating B vitamin deficiencies.

B vitamin levels can be measured with different individual blood tests:

  • Vitamin B1 (thiamin)
  • Vitamin B2 (riboflavin)
  • Vitamin B3 (niacin)
  • Vitamin B5 (pantothenic acid)
  • Vitamin B6 (pyridoxine)
  • Vitamin B7 (biotin)
  • Vitamin B9 (folate)
  • Vitamin B12 (cobalamin)

Alternatively, Vitamin Panels are available for the measurement of several B vitamins along with other vitamins.

If the vitamin B12 level is borderline, measuring methylmalonic acid (MMA) is a helpful next step. MMA provides a more direct measurement of vitamin B12's physiological activity, and an increase in MMA level indicates B12 deficiency.

Homocysteine can also be used to evaluate vitamin B12 deficiency, but it is not specific to this condition. Elevated homocysteine levels can also indicate vitamin B6 deficiency, folate deficiency, renal failure, or hypothyroidism.

How to Make Sure Your Patients are Getting Enough B Vitamins in Their Diet

The Recommended Daily Intake of B vitamins for adults is:

B vitamins can be obtained from different food sources. For example:

  • B1 (Thiamine) can be found in nuts, seeds, whole grains, legumes, and pork
  • B2 (Riboflavin) can be found in milk, cheese, yogurt, leafy greens, and eggs
  • B3 (Niacin) is present in meat, fish, whole grains, poultry, and nuts
  • B5 (Pantothenic acid) is found in meat, whole grains, fish, poultry, and legumes
  • B6 (Pyridoxine) can be obtained from meat, fish, poultry, whole grains, and fruits
  • B7 (Biotin) is present in egg yolks, seeds, nuts, and whole grains
  • B9 (Folate) can be found in leafy greens, fruits, and legumes
  • B12 (Cobalamin) is available in meat, poultry, fish, milk, and eggs

B vitamins can also be supplemented, and this is often recommended for certain populations. For example, perimenopausal and menopausal women experience a change in their nutrient needs. At this stage, vitamins and minerals like vitamin D, calcium, B vitamins, zinc, magnesium, and iron are critical in aiding hormonal shifts, so B vitamin supplements are useful along with others.

B vitamin supplementation has also been shown to enhance the effects of antidepressants over one year in patients with major depressive disorder, meaning this may be a beneficial supplement for those already taking antidepressants.

Iron, zinc, and B vitamins are all essential for the production of stomach acid, so those with low stomach acid may benefit from B vitamin supplementation as well.


B vitamins are essential micronutrients that play critical roles in various physiological processes in the human body. These include energy metabolism, DNA synthesis, and the proper functioning of the nervous system.

Measuring B vitamin levels is important because a deficiency of any of these vitamins can result in various health issues. Regular monitoring of B vitamin levels through blood tests helps identify deficiencies and allows for early intervention through dietary changes or supplementations. This is particularly important for people with medical conditions or those following restrictive diets, as they may be at higher risk for deficiency.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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