What Happens If the B Complex is Low: Symptoms, Causes, and Solutions

January 6, 2026 •

6 min read

According to the National Institutes of Health, a B complex deficiency can result from various factors, from inadequate dietary intake to underlying medical conditions. So, what happens if the B complex is low and what are the signs you should look for?

Quick Summary

A low B complex can manifest as a range of symptoms, including profound fatigue, neurological problems, and mood changes. This condition is often caused by poor dietary choices, malabsorption issues, or excessive alcohol use, and requires professional diagnosis and treatment.

Key Points

Fatigue and Anemia: A low B complex can cause profound fatigue and, in the case of B12 and B9 deficiency, result in megaloblastic anemia.
Neurological Impact: Neurological symptoms like numbness, tingling, memory issues, and impaired balance are common, especially with vitamin B12 deficiency.
Mood and Mental Health: Deficiencies in B6 and B12 are linked to psychological symptoms including depression, irritability, and anxiety.
Diverse Causes: Causes range from poor diet and excessive alcohol use to malabsorption conditions like Crohn's disease and certain medications.
Targeted Treatment: Treatment should be guided by a doctor and may involve dietary changes, oral supplements, or B12 injections, depending on the specific deficiency and underlying cause.

The B complex is a group of eight water-soluble vitamins that play critical roles in your body's cellular metabolism. These include thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin (B12). Because they are water-soluble, your body does not store them for long, meaning a consistent daily intake from food or supplements is necessary. When intake or absorption is inadequate, a deficiency can occur, leading to widespread and often serious health issues. The specific symptoms depend on which B vitamin is lacking, but many overlap.

The Wide-Ranging Symptoms of Low B Complex

The effects of a B complex deficiency can be categorized into physical, neurological, and psychological symptoms. These can often develop slowly over time, especially with B12 deficiency, making them easy to overlook in the early stages.

Physical Symptoms

Fatigue and weakness: Extreme tiredness is one of the most common signs, as B vitamins are vital for converting food into energy. A lack of B vitamins impairs this process, leading to persistent fatigue.
Anemia: Deficiencies in B12 and B9 (folate) can cause megaloblastic anemia, where red blood cells become abnormally large and are unable to function properly, reducing oxygen delivery throughout the body. This can result in paleness, shortness of breath, and an increased heart rate.
Skin and hair issues: A deficiency can cause various dermatological problems. For instance, low B7 (biotin) can lead to hair loss and a scaly red rash, while low B3 (niacin) can cause dermatitis. Cracks at the corners of the mouth (cheilosis) and a swollen, inflamed tongue (glossitis) can indicate deficiencies in B2 or B12.
Digestive problems: Gastrointestinal symptoms such as nausea, diarrhea, constipation, and loss of appetite are frequently reported. Severe B3 deficiency can lead to pellagra, which includes diarrhea as one of its hallmark signs.

Neurological Symptoms

Numbness and tingling: Often described as a "pins-and-needles" sensation, especially in the hands and feet. This is a common sign of vitamin B12 deficiency, which can cause nerve damage (peripheral neuropathy).
Trouble with balance and walking: Severe B12 deficiency can impair balance and cause difficulty walking due to its effect on the nervous system and spinal cord.
Vision problems: A rare but serious consequence of untreated B12 deficiency is optic neuropathy, which can cause gradual vision loss.
Cognitive and memory issues: Memory problems, confusion, and difficulty concentrating are all possible effects, particularly with low B12 and B9.

Psychological Symptoms

Mood changes: B vitamins, especially B6 and B12, are crucial for neurotransmitter synthesis. Low levels are linked to a higher risk of depression, irritability, and anxiety.
Paranoia and hallucinations: In severe cases of B12 deficiency, neuropsychiatric symptoms like psychosis, paranoia, and hallucinations can occur.

Common Causes of B Complex Deficiency

A deficiency can arise from several contributing factors, which may overlap.

Poor dietary intake: Restrictive diets, particularly vegan or strict vegetarian diets, are a primary cause of B12 deficiency since B12 is found almost exclusively in animal products. Insufficient intake of whole grains, leafy greens, and lean meats can also impact other B vitamin levels.
Malabsorption conditions: Certain digestive tract disorders can prevent the proper absorption of B vitamins. Conditions like Crohn's disease, celiac disease, and atrophic gastritis (a condition affecting stomach acid production, which is needed for B12 absorption) are major risk factors.
Excessive alcohol consumption: Alcohol interferes with the body's ability to absorb and utilize B vitamins. Excessive alcohol use causes the kidneys to flush B vitamins out of the system more rapidly than normal.
Medications: Certain prescription medications can deplete B vitamin levels. Examples include proton pump inhibitors (PPIs) and metformin (a diabetes drug), which can interfere with B12 absorption.
Increased bodily requirements: Pregnancy, breastfeeding, and aging can all increase the body's need for B vitamins. Older adults are also more likely to have reduced stomach acid, hindering B12 absorption.

Comparison: B12 vs. Folate Deficiency


Feature	Vitamin B12 Deficiency (Cobalamin)	Folate Deficiency (B9)
Onset of Symptoms	Slow, developing over years due to the body's storage capacity.	Relatively rapid, can develop within weeks.
Neurological Symptoms	Common and can be severe, including tingling, numbness, balance issues, and cognitive decline.	Typically does not cause neurological damage, except in cases of drug-induced deficiency.
Anemia Type	Megaloblastic and macrocytic, characterized by large, immature red blood cells.	Megaloblastic and macrocytic, identical in appearance to B12 deficiency anemia.
Metabolic Marker	Elevated levels of both homocysteine and methylmalonic acid (MMA) in the blood.	Elevated levels of homocysteine only; MMA levels remain normal.
Risk During Pregnancy	Low B12 can affect fetal neurological development.	Severe deficiency during pregnancy increases risk of neural tube defects like spina bifida.

Diagnosis and Treatment Options

If you suspect a B complex deficiency, it is crucial to consult a healthcare provider for a proper diagnosis. A diagnosis typically involves a physical examination, discussion of symptoms and lifestyle, and blood tests to measure levels of B vitamins and related metabolic markers like MMA and homocysteine.

Treatment depends on the specific vitamin(s) lacking and the underlying cause. For mild deficiencies, increasing dietary intake of B-rich foods may be sufficient. For more severe cases or malabsorption issues, doctors may prescribe oral supplements or, in the case of B12, intramuscular injections.

Conclusion

A low B complex can have a profound impact on your overall health, affecting everything from your energy levels and mood to your nervous system and cellular function. The diverse symptoms often overlap, making a medical evaluation necessary for accurate diagnosis and effective treatment. By understanding the causes and risks, and working with a healthcare provider, you can address deficiencies and restore proper balance to these vital nutrients. Taking proactive steps through diet and, if necessary, targeted supplementation can help prevent the serious, and sometimes irreversible, consequences of a prolonged B vitamin deficiency. For more information on B vitamins and their functions, the National Institutes of Health provides excellent resources (https://ods.od.nih.gov/factsheets/list-Vitamins-Minerals/).

A Balanced Approach to B Vitamins

Increase dietary intake: A balanced diet rich in leafy greens, lean meats, eggs, and fortified cereals is the first line of defense against B vitamin deficiencies.
Be aware of risk factors: Those with restrictive diets, gastrointestinal issues, or who use certain medications should be especially vigilant for deficiency symptoms.
Prioritize professional diagnosis: Self-diagnosing a B complex deficiency is not recommended. Consult a doctor for proper blood work and a personalized treatment plan.
Consider targeted supplementation: In cases of confirmed deficiency or malabsorption, your doctor may recommend specific B supplements or B12 injections rather than a general B complex.
Understand the signs: Recognizing the wide range of physical, neurological, and psychological symptoms associated with low B complex is key to seeking early intervention.

What to Eat to Prevent B Vitamin Deficiencies

Here are some examples of foods rich in various B vitamins:

B1 (Thiamine): Whole grains, lean pork, legumes, nuts, and seeds.
B2 (Riboflavin): Dairy products, eggs, lean meat, and green leafy vegetables.
B3 (Niacin): Chicken, turkey, fish, beef, nuts, and fortified cereals.
B5 (Pantothenic Acid): Organ meats, eggs, avocado, mushrooms, and broccoli.
B6 (Pyridoxine): Fish (tuna, salmon), potatoes, bananas, and poultry.
B7 (Biotin): Cooked eggs, nuts, and sweet potatoes.
B9 (Folate): Dark leafy greens, beans, legumes, citrus fruits, and liver.
B12 (Cobalamin): Animal products like meat, fish, dairy, and eggs. Vegetarians and vegans may need fortified foods or supplements.

Addressing Deficiency Effectively

Treating a B complex deficiency effectively requires more than just taking a supplement. It involves identifying and addressing the root cause, whether it's dietary, medical, or medication-related. A healthcare provider will determine the best course of action, ensuring you receive the proper dosage and form of the missing vitamin. Long-term management may be necessary for chronic conditions or dietary restrictions to maintain healthy B vitamin levels and prevent a recurrence of symptoms.

Frequently Asked Questions

The initial signs can be subtle and often include fatigue, weakness, mood changes like irritability, and a general lack of energy. Numbness or tingling in the hands and feet might also appear early, especially in a B12 deficiency.

Yes, a deficiency, particularly of vitamin B12, can lead to nerve problems. This can manifest as peripheral neuropathy, causing numbness, tingling, and a burning sensation in the limbs and extremities. If left untreated, the nerve damage can become irreversible.

Yes. While a vegan diet increases the risk of B12 deficiency, other factors can cause low B complex levels, even for meat-eaters. These include malabsorption issues from conditions like celiac or Crohn's disease, certain medications, excessive alcohol consumption, and aging, which can reduce absorption efficiency.

Both can cause macrocytic anemia, but the key difference is in the neurological symptoms and metabolic markers. B12 deficiency causes nerve damage and cognitive issues, while folate deficiency does not. A B12 deficiency elevates both homocysteine and methylmalonic acid (MMA), while folate deficiency only elevates homocysteine.

Research has linked low levels of certain B vitamins, particularly B6 and B12, to an increased risk of depression due to their role in neurotransmitter synthesis. However, supplements are not a cure for mental health conditions. They may help improve symptoms in those with a deficiency but should be used in consultation with a healthcare provider and not as a replacement for standard treatments.

Individuals at high risk include older adults, pregnant or breastfeeding women, people with gastrointestinal disorders (like Crohn's and celiac), heavy drinkers, and those on certain medications or restrictive diets like veganism.

Yes, because B vitamins are water-soluble and sensitive to heat, some cooking methods can reduce their nutritional content. For instance, boiling vegetables can cause some vitamins to leach into the water. Steaming or roasting can help preserve more of the vitamin content.