Researchers studied vitamin C levels in people with different stages of kidney disease and compared them to healthy people. They found that people with kidney problems tend to have much lower vitamin C levels than healthy individuals. The problem gets worse as kidney disease progresses, with people on dialysis having the lowest levels. The study suggests that both eating less vitamin C and losing it during dialysis treatment contribute to this problem. These findings highlight why doctors should pay closer attention to vitamin C status in kidney disease patients.

The Quick Take

  • What they studied: Whether people with kidney disease have lower vitamin C levels than healthy people, and what causes these differences
  • Who participated: 1,039 people total: 145 with various stages of kidney disease (including those on dialysis and those who received transplants) and 832 healthy people (including kidney donors and general healthy controls)
  • Key finding: People with advanced kidney disease had vitamin C levels 2-3 times lower than healthy people. About 80% of people with the most severe kidney disease had inadequate or deficient vitamin C, compared to only 14% of healthy people
  • What it means for you: If you have kidney disease, you may need to pay special attention to vitamin C intake and have your levels checked regularly. However, more research is needed to understand if low vitamin C actually causes health problems in kidney disease patients

The Research Details

This was a cross-sectional study, which means researchers took a snapshot in time of vitamin C levels in different groups of people. They measured the actual amount of vitamin C in the blood of 1,039 people: some with healthy kidneys, some who had donated a kidney, some with different stages of kidney disease, and some on dialysis treatment. They also looked at how much vitamin C people were eating through food and supplements, and measured how much vitamin C was removed during dialysis sessions.

The researchers used blood tests to measure vitamin C levels and defined three categories: deficient (very low), inadequate (low but not critically), and adequate (normal). They also looked at dietary records to see how much vitamin C people were consuming daily. For people on dialysis, they actually measured how much vitamin C was being removed from their blood during treatment.

Understanding vitamin C status in kidney disease is important because vitamin C plays many roles in the body, including supporting the immune system and helping wounds heal. If kidney disease patients are consistently low in vitamin C, it could affect their overall health. This study helps doctors understand the scope of the problem and what might be causing it, which is the first step toward developing solutions.

This study has several strengths: it included a large number of people (over 1,000), it measured actual blood vitamin C levels rather than just asking people what they ate, and it looked at different stages of kidney disease separately. However, because it’s a snapshot in time rather than following people over months or years, we can’t be completely sure about cause and effect. The study also doesn’t tell us whether low vitamin C actually causes health problems in these patients.

What the Results Show

The study found a clear pattern: vitamin C levels dropped as kidney disease got worse. Healthy people had a median vitamin C level of 58 units, while people with the most advanced kidney disease (stage 4/5) had only 22 units—less than half. People on dialysis had slightly higher levels (33 units) because many of them were taking vitamin C supplements, but this was still much lower than healthy people.

When the researchers looked at how many people had inadequate or deficient vitamin C, the differences were striking. Only 14% of healthy people fell into these categories, but 80% of people with advanced kidney disease did. Even kidney transplant recipients, who generally do better than dialysis patients, had 48% with inadequate or deficient levels.

The study also revealed why these problems occur. People with advanced kidney disease weren’t eating much more vitamin C than they should—in fact, many weren’t getting enough through diet. Additionally, dialysis treatment actually removes vitamin C from the blood. A regular dialysis session removed about 58 milligrams of vitamin C, while more intensive nocturnal dialysis removed even more (128 milligrams).

The researchers found that in healthy people, kidney function (measured by eGFR) was positively linked to vitamin C levels—meaning people with better kidney function tended to have higher vitamin C. This relationship was independent of other factors like age and diet. Interestingly, people who had donated a kidney (and thus have one kidney instead of two) had vitamin C levels between healthy controls and kidney disease patients, suggesting that having reduced kidney function affects vitamin C status even in otherwise healthy people.

This research adds important detail to what was already known: vitamin C deficiency is a recognized problem in kidney disease patients. However, this study is one of the first to systematically measure vitamin C levels across the entire spectrum of kidney disease severity and to measure how much vitamin C is actually removed during dialysis. Previous research had identified the problem but not fully characterized how common it is or what causes it.

This study is a snapshot in time, so we can’t know if vitamin C levels stay the same or change over time in individual patients. The study measured vitamin C status but didn’t follow patients to see if low vitamin C actually caused health problems. Additionally, the study didn’t test whether giving vitamin C supplements would improve outcomes. The findings may not apply equally to all populations, as the study participants were primarily from one healthcare system.

The Bottom Line

If you have kidney disease, especially advanced stages, ask your doctor to check your vitamin C levels. Eating more vitamin C-rich foods (like citrus fruits, berries, and vegetables) may help, though the study suggests this alone may not be enough for dialysis patients. Some kidney disease patients may benefit from vitamin C supplements, but this should only be done under medical supervision because too much vitamin C can be harmful in kidney disease. Confidence level: Moderate—the evidence clearly shows the problem exists, but we need more research on solutions.

People with chronic kidney disease, especially those with advanced stages or on dialysis, should pay attention to these findings. Kidney transplant recipients should also be aware. Healthy people generally don’t need to worry about this, though those who have donated a kidney might want to discuss vitamin C status with their doctor. Healthcare providers caring for kidney disease patients should consider monitoring vitamin C levels as part of routine care.

If vitamin C deficiency is corrected through diet or supplements, some effects (like improved immune function) might be noticed within weeks to months. However, we don’t yet know the full timeline for health improvements because this research hasn’t been done. Long-term monitoring would be needed to see if correcting vitamin C status prevents complications.

Want to Apply This Research?

  • If you have kidney disease, track your daily vitamin C intake from food and supplements (in milligrams). Set a target based on your doctor’s recommendations and log foods like oranges, berries, tomatoes, and peppers. Also note any vitamin C supplements you take.
  • Work with your healthcare team to gradually increase vitamin C-rich foods that are appropriate for your kidney disease diet. For example, if you can tolerate them, add small amounts of citrus fruits, berries, or bell peppers to meals. If supplements are recommended, set a daily reminder to take them at the same time each day.
  • Request vitamin C blood level tests from your doctor every 3-6 months if you have advanced kidney disease. Track the results in your app and note any changes in how you feel (energy levels, wound healing, immune function). Share this data with your healthcare team to adjust your vitamin C plan as needed.

This research shows that vitamin C levels are often low in kidney disease patients, but it does not prove that low vitamin C causes health problems or that supplements will help. If you have kidney disease, do not start taking vitamin C supplements without talking to your doctor first, as too much vitamin C can be harmful for people with kidney problems. This information is for educational purposes and should not replace medical advice from your healthcare provider. Always consult with your nephrologist (kidney specialist) before making changes to your diet or supplements.