B vitamins act as coenzymes in several enzymatic processes that support every aspect of life, including energy production and central nervous system functions. Like other vitamins and minerals, B vitamins occur naturally in food and are consumed as part of a well-rounded diet.
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Of the 13 vitamins our body needs to function, 8 are B vitamins. B vitamins are water-soluble and are excreted in the urine if consumed in excess. Therefore, daily consumption of B vitamins is required to maintain optimal levels and physiological functioning. With so many B vitamins and functions, it can get confusing to keep them all straight. Continue reading for an overview of each B vitamin, followed by more information on the one most people need to catch up on.
B Vitamins in Review
B1 (Thiamin): Found in foods like whole grains, pork, nuts, legumes, fish, yeast, and fortified food products, thiamine plays a significant role in energy production. As a cofactor for the citric acid cycle, the pentose phosphate pathway, and aerobic metabolism, thiamine helps convert nutrients into energy. Therefore, low thiamine levels can cause reduced energy production and cell death. This is of particular concern for neurons, which are more vulnerable to alterations in energy production due to their high energy demand.
Thiamin deficiency can lead to mild symptoms such as fatigue or anorexia, including more severe side effects such as Beriberi, Wernicke-Korsakoff syndrome, endocarditis, arrhythmia, or sudden death. The Recommended daily intake (RDI) for adults is 1.2mg for men, 1.1mg for women, and 1.4mg for women when pregnant. According to the literature, erythrocyte transketolase activity assay, including thiamine pyrophosphate (TPP), is the most reliable measure of thiamine levels.
B2 (Riboflavin): Found naturally in eggs, dairy products, green vegetables, and meat and added to fortified foods, riboflavin is needed for macronutrient metabolism into glucose and is essential for synthesizing all heme proteins.
Riboflavin deficiency can lead to various symptoms, such as skin abnormalities, anemia, hair loss, depression, fatigue, and nervous system issues. People at higher risk for riboflavin deficiency include those on medications such as anticonvulsants, anticholinergics, and phenothiazine, as well as those with liver disease, alcoholism, or hemodialysis. The RDI for B2 is 1.3mg for men, 1.1mg for women, and 1.4mg for pregnant women. Evidence indicates that the erythrocyte glutathione reductase activity coefficient is the most sensitive test for vitamin B2 levels.
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B3 (Niacin): Found in various foods, including soy, nuts, seeds, legumes, and grains, and fortified foods, niacin plays vital roles in DNA production and repair. Niacin deficiency can result in various symptoms such as depression, anxiety, memory loss, burning and twitching in the extremities, and pellagra, a condition characterized by dementia, diarrhea, and dermatitis.
The RDI for Niacin is 16mg for men, 14mg for women, and 18mg for pregnant women. Niacin also has an upper limit of dietary intake of 35mg/d, as higher doses may lead to side effects such as flushing, macular edema, and liver toxicity. Low iron, riboflavin, or vitamin B6 may decrease niacin synthesis. Testing for niacin is not widely available.
B5 (Pantothenic Acid): B5 is found in high amounts mushrooms, eggs, fish, avocados, chicken, pork, sunflower seeds, sweet potatoes, legumes, and fortified foods. Vitamin B5 is vital for synthesizing and maintaining coenzyme A (CoA). CoA is well known for its role in synthesizing and oxidizing fatty acids and pyruvate in the citric acid cycle. These physiological pathways are required for life; therefore, pantothenic acid is essential to almost all lifeforms.
If deficient in B5, symptoms may include diarrhea, numbness, burning sensations, dermatitis, or more serious nervous system side effects such as encephalopathy, demyelination, insomnia, or behavioral changes. The RDI for pantothenic acid is 5mg for men and women and 6mg if pregnant. Vitamin B5 status can be measured via radioimmunoassay or 24-hour urinary excretion.
B6 (Pyridoxine): Found in beef, poultry, starchy vegetables, and fortified cereals, vitamin B6 is a coenzyme that plays a role in multiple pathways responsible for red blood cell production, immune function, brain health, and the metabolism of macronutrients. Individuals with mild B6 deficiency may show no signs or symptoms for months or years. However, more severe deficiency is associated with microcytic anemia, cognitive impairment, peripheral neuropathy, dermatitis with cheilosis, glossitis, depression, confusion, and weakened immune systems.
Pyridoxine deficiency incidence is higher among those with chronic alcohol use, renal failure, autoimmune disease, obesity, pregnancy, and malabsorptive conditions such as celiac disease, inflammatory bowel disease, and bariatric surgery. The RDI for B6 is 1.7mg for men and women and 1.9mg for pregnant women. B6 levels can be assessed by erythrocyte transaminase activity or urinary pyridoxic acid excretion.
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B7 (Biotin): Found in organ meats, eggs, fish, seeds, soybeans, and nuts, biotin plays essential roles in gene regulation, cell signaling, replication, and the metabolism of macronutrients. Biotin deficiency is associated with hair thinning, skin rash or infection, nail changes, and neurological symptoms such as ataxia, seizures, depression, lethargy, and paresthesia. While rare, biotin deficiency can occur in those with alcoholism, chronic use of epileptic medications, or in those who are pregnant or breastfeeding. The RDI for biotin is 30mcg daily for both men and women.
Based on the current evidence, serum biotin levels are not sensitive enough to reflect status. Still, biotin can be assessed by measuring urinary excretion of 3-hydroxy isovaleric acid.
B9 (Folate): Folate is present in various foods, with the highest levels in dark leafy vegetables, nuts, beans, eggs, dairy products, meat, and poultry. Folate is crucial for nucleic acid synthesis and red blood cell production. Therefore, folate deficiency can lead to megaloblastic anemia. Folate deficiency symptoms may include weakness, fatigue, poor concentration, irritability, peripheral neuropathy, behavioral changes, dementia, headaches, and palpitations. Deficiency can also lead to changes in skin, hair, and fingernails. Certain groups of people are at higher risk for folate deficiency, including women of childbearing age, Black women, or those with genetic mutations that reduce their ability to convert folic acid into its active form.
The RDI for B9 is 400mcg for men and women and 600mcg for those who are pregnant. Folate status can be assessed using homocysteine levels, which will rise with folate deficiency. However, B12 deficiency must also be ruled out, as both can increase homocysteine levels. Erythrocyte folate concentration may help confirm a long-term deficit.
B12 (Cobalamin): Vitamin B12 is found in animal products such as liver, meat, milk, cheese, eggs, and fortified food. Cobalamin is required for DNA and RNA synthesis, red blood cell production, neurologic function, myelin synthesis, protein and lipid synthesis, and metabolism. Symptoms associated with B12 deficiency include megaloblastic anemia, fatigue, low appetite, and neuropsychiatric symptoms. If not addressed early enough, the neurological symptoms of B12 deficiency may become permanent. The groups most affected by B12 deficiency include older adults, patients with pernicious anemia, pregnant or lactating women, and those with chronic use of medications like proton pump inhibitors, H2 receptor antagonists, and metformin.
The RDI for vitamin B12 is 2.4 mcg for men and women and 2.6 mcg for those who are pregnant. Cobalamin levels can be assessed via serum B12 concentrations and elevated homocysteine or methylmalonic acid (MMA) levels. Of the testing methods, MMA is the most sensitive, specific, and accurate indicator of vitamin B12 status and can be measured in the plasma or urine (uMMA).
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The B Vitamin to Look out for
Of all eight B vitamins, vitamin B12 is the one people most often fall short on. The reason obtaining adequate B12 levels can be a challenge is multifactorial. First, it is the only B vitamin found exclusively in animal products (naturally, at least). So, anyone who consumes limited animal products is at risk for deficiency.
Additionally, pregnant women or those taking certain medications, specifically those used to treat heartburn, such as proton pump inhibitors (PPIs), are at risk for B12 deficiency.
Furthermore, the absorption of B12 is dependent on a healthy gastrointestinal (GI) tract. So, people who have had GI surgery or have a clinical condition that causes GI inflammation may be unable to absorb B12 efficiently.
Finally, absorption of B12 in the gut tends to decrease with age, so the elderly are another group of people who are more at risk for deficiency. B12 deficiency can lead to severe cognitive and nervous system consequences that may be permanent if not resolved early on. Keeping an eye on vitamin B12 status may benefit anyone in one of these high-risk categories.
B vitamins play a role in many critical pathways of human physiology. Because they are water-soluble, they will not be stored in large quantities and must be consumed regularly to maintain optimal levels. They are found in various foods, with the highest amounts in animal products or foods fortified with B vitamins.
Some of the most common reasons for B vitamin deficiency include decreased intake of foods high in B vitamins, impaired absorption of B vitamins related to gastrointestinal procedures or malabsorptive conditions, pregnancy or lactation, alcoholism, long-term use of certain medications, or genetic diseases which inhibit the use of B vitamins.
Vitamin B deficiency symptoms can vary from fatigue and lethargy to permanent neurological disorders. Testing is available for most B vitamins, and B12 can be tested easily by assessing uMMA levels. If a B vitamin deficiency is found, supplementation may be indicated. Head here for more information on choosing the right B vitamin supplement.