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Pyridoxine Deficiency

What Is It, Causes, Diagnosis, and More

Author: Lily Guo

Editors: Alyssa Haag, Józia McGowan, DO

Illustrator: Jillian Dunbar

Copyeditor: David G. Walker

What is pyridoxine deficiency?

Pyridoxine deficiency refers to low levels of pyridoxine, or vitamin B6, in the body. Vitamin B6 is a water-soluble vitamin found naturally in many food sources and can be added to foods and supplements. It is essential for normal brain development and for keeping the nervous system and immune system healthy. 

How common is pyridoxine deficiency?

Since vitamin B6 is present in most foods, dietary deficiency is rare. Secondary deficiency may result from various conditions. Individuals with impaired renal function who are receiving dialysis or have received a transplant are more likely to experience vitamin B6 deficiency. This is due to increased metabolic clearance of pyridoxal 5 phosphate (PLP), which is the biologically active form of vitamin B6. Additionally, those with autoimmune disorders, such as celiac disease, and inflammatory bowel diseases (e.g., Crohn disease and ulcerative colitis), are more prone to have deficiencies as a result of decreased absorption by the gut and increased inflammation caused by the underlying disease. Lastly, those with alcohol dependence are also at a greater risk. Alcohol is broken down to acetaldehyde, which decreases total PLP. Overall, isolated vitamin B6 deficiency is uncommon. Instead,  inadequate vitamin B6 status is usually associated with low concentrations of other B-complex vitamins, such as vitamin B12 and folic acid (i.e., vitamin B9). 

What causes pyridoxine deficiency?

There can be several causes of pyridoxine deficiency, including consuming less than the recommended dietary allowance (RDA) per day. For men ages 14-50, the RDA is 1.3mg; 51+ years, 1.7 mg. For women 4-18 years, it is 1.2 mg; 19-50 years, 1.3 mg; 51+ years, 1.5 mg. This amount increases to 2.0mg in those who are pregnant or lactating. The richest sources of vitamin B6 include fish, beef liver and other organ meats, potatoes and other starchy vegetables, and non-citrus fruits. In the United States, adults also obtain a lot of their dietary vitamin B6 intake from fortified cereals and poultry. Notably, vitamin B6 found in meats are more easily absorbed and used by the body than vitamin B6 from plants and vegetables, which may be important to those who exclusively follow a vegetarian or vegan diet. 

Another well-known cause of pyridoxine deficiency is the use of isoniazid, an antibiotic drug used to prevent and treat tuberculosis. Isoniazid causes a depletion of vitamin B6 by inhibiting an enzyme (pyridoxine phosphokinase) necessary for pyridoxine synthesis.

What are the signs and symptoms of pyridoxine deficiency?

Individuals with borderline vitamin B6 concentrations or mild deficiency might have no signs or symptoms for months or even years. Those with prolonged or severe pyridoxine deficiency may experience peripheral neuropathy and a pellagra-like syndrome. Pellagra is a disease that occurs when a person does not receive enough of vitamin B3, or niacin. It is characterized by dermatitis, dementia, and diarrhea. In those with pyridoxine deficiency, individuals may often experience skin conditions, such as seborrheic dermatitis, which is characterized by a red, itchy rash on the scalp, face, neck and upper chest. It typically has an oily, flaky appearance and may cause swelling or white patches. One of the functions of vitamin B6 is to produce collagen, a protein in the skin that provides strength and elasticity. Without adequate levels of Vitamin B6, the skin barrier may break down, leading to dermatological conditions. Cheilosis (i.e., scaling on the lips and cracks at the corners of the mouth) and glossitis (i.e., swollen tongue) are also characteristic signs. In the case of glossitis, the tongue becomes enlarged, smooth, and red as it loses the papillae, or raised protrusions, on the tongue. 

Importantly, deficiency of B6 can cause nerve damage, leading to burning, shooting and tingling pain in the arms, legs, hands, and feet. It may feel like “pins and needles” and can also result in clumsiness, balance problems, and difficulty walking. Individuals may also experience confusion, depression, electroencephalogram abnormalities, seizures, and a weakened immune system. Vitamin B6 is necessary for the production of antibodies and white blood cells, such as T cells, needed to fight infection. Without these cells regulating the immune function, it is unable to respond appropriately. Additionally, microcytic anemia, characterized by the presence of small, pale  red blood cells, can also occur as the body needs vitamin B6 to make hemoglobin and increase the amount of oxygen carried by hemoglobin. In infants, vitamin B6 deficiency causes irritability, abnormal hearing, and convulsive seizures. 

How is pyridoxine deficiency diagnosed?

Pyridoxine deficiency can be diagnosed by clinical evaluation and physical examination. Clinicians may look for the key signs of deficiency, including dermatological findings, presence of altered mental status, and peripheral neuropathy. They can also take a focused history and obtain records of nutritional intake, supplement use, and medication history. Also critically important is eliciting a history of increased risk, including those with malabsorption syndromes, such as inflammatory bowel disease, celiac disease, or history of bariatric surgery. 

The exam should also be age focused. In a neonate with seizures and mothers with poor nutritional status, vitamin B6 deficiency may be suggested. It should also be considered in any infant who has seizures; an adult who has seizures refractory to treatment with antiseizure drugs; adults with deficiencies of the other B vitamins, including niacin and cobalamin (i.e. B12); and particularly in individuals with an alcohol use disorder or malnutrition. Diagnosis of vitamin B6 deficiency is usually made based on a clinical exam; however, deficiency can also be detected by direct assay of blood or urine. Nerve conduction studies may also reveal severely reduced sensory nerve action potentials, and nerve biopsy can assess for degeneration of small and large myelinated nerve fibers.

How is pyridoxine deficiency treated?

Pyridoxine deficiency can be treated with vitamin B6 supplements. Vitamin B6 is available in multivitamins, in supplements containing other B complex vitamins, and as a stand-alone supplement. It is used by approximately 28%–36% of the general population. Usually, pyridoxine dosed at 50 to 100mg orally once a day will correct the deficiency in adults. 

Supplementation protocols may vary depending on the specific cause of the deficiency. Most people taking isoniazid should be given 30 to 50mg of pyridoxine orally once a day. For metabolic disorders or increased metabolic demand, taking high doses or increasing daily recommended intake of pyridoxine may be required after consulting with a clinician. 

It is important to note that pyridoxine is one of the three water-soluble vitamins that can have toxicity at excessive doses, in addition to niacin (i.e. vitamin B2) and ascorbic acid (i.e. vitamin C).

What are the most important facts to know about pyridoxine deficiency?

Pyridoxine deficiency refers to insufficient levels of pyridoxine, or vitamin B6, in the body. It can be caused by low daily intake of the vitamin through diet or supplements, or from secondary causes, such as alcohol dependence, renal failure, or certain medication use. Symptoms of vitamin B6 deficiency include dermatitis with cheilosis, glossitis, and peripheral neuropathy. Vitamin B6 deficiency is not very common in the general population since the vitamin can be naturally found in many foods; however, it can become a problem in those experiencing malnutrition, those who follow a diet lacking meat, or those with underlying disorders that lead to malabsorption. Diagnosis involves a physical exam by a clinician along with lab tests for serum levels of vitamin B6. Treatment depends on disease severity. The clinician may choose to offer supplements, especially if the individual is taking isoniazid or has inadequate intake through their diet. 

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