How to use vitamin C without harming the kidneys?

Vitamin C is beneficial for people with kidney failure, reducing the risk of kidney cancer, but if used in high doses regularly it can be harmful.

Vitamin C is an important nutrient for the body, helping to absorb iron from food, heal wounds and bruises on the skin, and support bone repair.

According to the US National Institutes of Health (NIH), the amount of vitamin C needed for adult men is 90 mg per day, and for women is about 75 mg per day. Smokers need about 35 mg more vitamin C, as smoking increases oxidative stress, reducing vitamin levels.

The kidneys have the function of filtering excess vitamin C out of the body. However, if the kidneys do not function normally or regularly consuming high amounts of vitamin C can cause some health risks.

A 2023 review by the Finnish University of Medicine found that vitamin C may be anti-inflammatory and antioxidant for people with chronic kidney disease. People on hemodialysis may also be recommended vitamin C supplements. A 2021 review in Finland found that dialysis reduced vitamin C levels by 67% on average in 138 participants.

However, high levels of vitamin C can be harmful to people with chronic kidney disease . For example, if you consume 30-180 mg of vitamin C per day, the body usually absorbs 70-90% of this amount. The kidneys then excrete the excess through urine.

Vitamin C can be converted to oxalate, which is also filtered by the kidneys. The kidneys of people with this chronic disease are no longer able to filter waste effectively, and can accumulate oxalate in the body, leading to kidney stones, inflammation, and kidney failure.

High doses of vitamin C increase the risk of kidney stones, most commonly calcium oxalate. Vitamin C intake from food is unlikely to cause this condition, but care should be taken when supplementing with supplements.

To reduce the risk of kidney stones, the NIH recommends that adults consume no more than 2,000 mg of vitamin C per day.

Oranges are rich in vitamin C. (Photo: Ha Phuong).

For people with kidney cancer, vitamin C can have a positive impact. According to a 2022 review by Chinese researchers, increased vegetable and vitamin C intake is associated with a reduced risk of kidney cancer.

A 2015 meta-analysis also assessed that people with higher vitamin C intake had a lower risk of kidney cancer. A 2019 study in the US also showed that vitamin C supplementation can increase the effectiveness of chemotherapy in people with kidney cancer without increasing side effects.

However, the US National Cancer Institute (NCI) recommends against using high doses of vitamin C for kidney cancer patients because it may cause more harm.

The body cannot make vitamin C and must absorb it from foods or supplements. This nutrient is found throughout the body, so health experts often use blood levels of vitamin C to assess each person's vitamin intake.

Many fruits and vegetables are rich in vitamin C such as red and green bell peppers, strawberries, kiwis, oranges, grapefruits, potatoes, tomatoes, cabbage, cauliflower. People who do not get enough vitamin C through their diet You should consult your doctor about appropriate vitamin C supplementation to avoid the risk of affecting the kidneys.