9 Vitamins & Supplements That May Affect Your Liver and Kidneys If Misused
Vitamins and supplements are often marketed as harmless because they are available without a prescription. But “natural” does not automatically mean risk-free.
The liver processes many substances that enter the body, while the kidneys filter the blood and remove waste products. Taking excessive doses, combining several supplements, or using concentrated herbal extracts can sometimes place extra stress on these organs.
For most healthy people, vitamins taken at recommended amounts are unlikely to cause serious problems. The greater
concern is usually **high-dose or prolonged supplementation**, particularly in people who already have liver or kidney disease.
Here are nine vitamins and supplements worth using carefully.
## 1. Vitamin A
Vitamin A is essential for vision, immunity, reproduction, and normal cell growth.
However, excessive intake of **preformed vitamin A**, such as retinol or retinyl palmitate, can accumulate in the body because vitamin A is fat-soluble.
Very high or prolonged doses can potentially cause:
* liver enzyme abnormalities
* liver injury
Possible symptoms include:
* nausea
* vomiting
* weakness
* confusion
* excessive thirst
* frequent urination
* dehydration
Very high vitamin D levels may lead to **kidney stones and, in severe cases, kidney failure**.
People taking high-dose vitamin D for a documented deficiency should follow the dose and monitoring plan recommended by their healthcare professional.
## 3. Vitamin C
Vitamin C is water-soluble, so excessamounts are largely eliminated through urine.
That does not mean extremely high doses are harmless.
Large supplemental doses may increase the amount of oxalate in the urine. In susceptible people, this can contribute to the formation of **calcium oxalate kidney stones**.
People who already have:
* kidney disease
* a history of kidney stones
* disorders that increase oxalate absorption
should be particularly cautious with high-dose vitamin C supplements.
Getting vitamin C from ordinary foods such as citrus fruits, berries, peppers, and vegetables is generally not the concern. The issue is primarily concentratedsupplements taken in much larger amounts than the body requires.
## 4. Niacin — Vitamin B3
Niacin is an essential B vitamin, but high doses of nicotinic acid have also been used medically to influence cholesterol levels.
At nutritional doses, niacin is not normally associated with liver damage.
At pharmacological doses, however, it can cause elevations in liver enzymes and, in some cases, clinically significant liver injury.
Certain sustained- or extended-release formulations have been particularly associated with liver toxicity when used improperly.
Possible warning signs can include:
* unusual fatigue
* persistent nausea
* painin the upper abdomen
* dark urine
* yellowing of the skin or eyes
High-dose niacin should not be treated like an ordinary daily vitamin.
## 5. Iron Supplements
Iron is essential for producing hemoglobin and carrying oxygen through the body.
Iron supplements can be very useful when someone has confirmed iron deficiency, but taking iron when it is not needed can be harmful.
Unlike some nutrients, the body has limited ability to eliminate excess iron.
Large amounts can accumulate and potentially damage organs, including the **liver**. NIH guidance notes that excess ironmay damage the liver and other organs.
This is why iron should generally not be taken long-term simply because someone feels tired.
Fatigue has many causes, and blood tests can help determine whether iron deficiency is actually present.
### Warning:
Accidental iron overdose can be particularly dangerous in children, so iron supplements should always be stored securely.
## 6. Green Tea Extract
Drinking ordinary brewed green tea is generally very different from taking a concentrated green tea extract.
Green tea extracts are found in some:
* weight-loss products
* “fat burner” supplements
* energy formulasantioxidant supplements
Concentrated extracts have been linked to cases of acute liver injury.
NIH’s LiverTox database documents clinically apparent liver injury associated with green tea extract, including rare severe cases requiring transplantation.
The risk appears to be uncommon, but it illustrates an important point: concentrating a plant into capsules can expose the body to much larger doses of certain compounds than drinking the plant as a normal beverage.
## 7. Kava
Kava is an herbal product sometimes promoted for relaxation, stress, or sleep.
However, kava supplements have been associated with casesof serious liver injury.
Reported problems have included:
* hepatitis
* severe liver damage
* liver failure
* rare cases requiring liver transplantation
The FDA has previously issued warnings about the potential for severe liver injury with kava-containing supplements.
