What are the side effects of taking vitamin A?

October 26, 2025 •

3 min read

While essential for vision, immunity, and cell growth, excessive vitamin A intake can be dangerous, with toxicity most commonly caused by supplements or medications, not food. This article explores what are the side effects of taking vitamin A when consumed in high amounts, a condition known as hypervitaminosis A.

Quick Summary

Excessive intake of preformed vitamin A, typically from supplements or certain medications, can cause hypervitaminosis A, leading to severe side effects affecting the skin, liver, bones, and nervous system, varying based on dosage and duration.

Key Points

Source of Risk: Toxicity (hypervitaminosis A) primarily occurs from excessive preformed vitamin A in supplements or animal sources like liver, not from provitamin A carotenoids in fruits and vegetables.
Acute vs. Chronic Effects: Acute toxicity from a single large dose can cause severe symptoms like nausea and headache, while chronic toxicity from long-term overuse leads to progressive issues such as dry skin, hair loss, and fatigue.
Liver Damage: A significant side effect of chronic vitamin A toxicity is liver damage, which can lead to serious conditions like fibrosis and cirrhosis over time.
Bone Weakening: Long-term, high intake of vitamin A is associated with an increased risk of osteoporosis and fractures, especially in older adults.
Pregnancy Warning: High doses of preformed vitamin A during pregnancy can cause severe birth defects, making it crucial for pregnant women to monitor their intake and avoid excessive amounts.
Intracranial Pressure: Excessive vitamin A, both acute and chronic, can cause increased pressure within the skull, leading to symptoms like severe headaches and vision problems.

Understanding Vitamin A Toxicity (Hypervitaminosis A)

Vitamin A is a fat-soluble nutrient stored in the liver. Excessive amounts can accumulate over time, leading to hypervitaminosis A. Toxicity from food sources, like provitamin A carotenoids, is unlikely; the risk primarily stems from over-consuming preformed vitamin A in supplements, animal products (especially liver), or medications.

Acute vs. Chronic Vitamin A Toxicity

Vitamin A toxicity presents differently depending on the dose and duration of excessive intake.

Acute Toxicity

This results from a single, large dose of vitamin A. Symptoms often appear within hours or days. These can include nausea, vomiting, severe headache, dizziness, blurred vision, and skin peeling. Infants may show increased intracranial pressure with a bulging fontanelle.

Chronic Toxicity

Chronic toxicity develops from prolonged intake of excessive doses over months or years. This leads to a gradual accumulation and systemic issues. Symptoms include dry skin, hair loss, bone and joint pain, and fatigue. Liver damage is a significant concern.

Side Effects by Body System

Excessive vitamin A can impact various organ systems.

Dermatological and Mucous Membrane Issues

Beyond dry skin and hair loss, effects can include dry eyes, cracked lips, and skin conditions like exfoliative dermatitis.

Neurological Effects

Increased pressure within the skull (idiopathic intracranial hypertension) can cause persistent headaches and vision problems. Chronic toxicity may also lead to drowsiness and confusion.

Musculoskeletal System

Long-term high intake is linked to decreased bone density and increased fracture risk. Elevated blood calcium levels (hypercalcemia) and bone pain are also possible.

Liver and Other Metabolic Changes

Excess vitamin A can result in elevated liver enzymes, an enlarged liver and spleen (especially in children), and increased blood lipid levels (hyperlipidemia). Chronic excess can lead to liver damage like fibrosis and cirrhosis.

Reproductive and Developmental Risks

High vitamin A intake during pregnancy significantly increases the risk of birth defects, particularly affecting the head, heart, and central nervous system. High-dose beta-carotene supplements have also been linked to an increased risk of lung cancer in smokers.

Comparison of Acute vs. Chronic Hypervitaminosis A


Feature	Acute Hypervitaminosis A	Chronic Hypervitaminosis A
Onset	Sudden, within hours or days	Gradual, over months or years
Cause	Single, very large dose	Long-term intake of moderately high doses
Key Symptoms	Nausea, vomiting, severe headache, irritability, drowsiness, skin peeling	Dry skin, hair loss, bone/joint pain, fatigue, liver damage
Reversibility	Usually reversible with discontinuation, though severe cases may have lasting damage	Symptoms slowly resolve with discontinuation; organ damage may be irreversible
Risk Group	Accidental ingestion, especially by children	Individuals with long-term high-dose supplement use or excessive intake of animal-based vitamin A sources

Avoiding Vitamin A Toxicity

To prevent hypervitaminosis A, avoid exceeding the tolerable upper intake level (UL) for preformed vitamin A, which is 3,000 mcg (10,000 IU) per day for most adults. Be cautious with supplements and frequent consumption of foods high in preformed vitamin A, like liver. Always consult a healthcare professional before starting supplements, especially if pregnant or taking high doses.

Conclusion

While essential, excessive vitamin A intake can lead to hypervitaminosis A, causing side effects ranging from acute issues like headache and vomiting to chronic problems like liver damage, bone weakening, and birth defects. The risk is highest from supplements and certain animal products. Adhering to recommended intake levels and consulting healthcare providers can help individuals safely benefit from vitamin A while avoiding these harmful effects.

For more detailed information on vitamin A, consult the Office of Dietary Supplements, a resource from the National Institutes of Health(https://ods.od.nih.gov/factsheets/VitaminA-Consumer/).

Frequently Asked Questions

Taking a single, very large dose of vitamin A can cause acute toxicity, with symptoms appearing within hours. These include nausea, vomiting, severe headache, dizziness, and peeling skin.

Yes, in most cases, the symptoms of vitamin A toxicity are reversible by stopping the intake of the excess vitamin. However, severe or prolonged toxicity can lead to irreversible organ damage, such as liver cirrhosis.

No, it is highly unlikely to develop vitamin A toxicity from dietary carotenoids found in fruits and vegetables like carrots. Excessive intake of carotenoids may cause a harmless yellow-orange skin discoloration (carotenosis), but not toxicity.

For most adults, the tolerable upper intake level (UL) for preformed vitamin A is 3,000 mcg (10,000 IU) per day. Regularly exceeding this amount, especially from supplements, increases the risk of toxicity.

High doses of preformed vitamin A during pregnancy are a significant risk for birth defects, especially during the first trimester. Pregnant women and those planning a pregnancy should avoid supplements above the recommended daily allowance.

Children are more sensitive to vitamin A and can develop toxicity at lower doses than adults. Acute toxicity in infants can cause increased intracranial pressure, sometimes indicated by a bulging fontanelle.

To avoid toxicity, do not exceed the tolerable upper intake level for preformed vitamin A, especially from supplements. If you eat a lot of animal liver, you should avoid supplements containing vitamin A. Always consult a healthcare provider before taking supplements.