Why Vitamin C for UTI Doesn’t Work

Can I take vitamin C for UTI?

Ascorbic acid (vitamin C) is often recommended as a supplement that can prevent recurrent urinary tract infections (rUTI) by acidification of the urine. However, there is no strong clinical evidence to support this claim.

The good news is that vitamin C is a valuable supplement that has all kinds of benefits, per Healthline.com: “boosting antioxidant levels, reducing blood pressure, reducing heart disease risk, protecting against gout attacks, improving iron absorption, boosting immunity and reducing dementia risk.”

At the same time, only a couple of clinical research studies have been done on the protective effects of vitamin C against recurrent UTIs and have arrived at contradicting conclusions.

For example, one study looked at the ability of vitamin C (in the form of ascorbic acid) to acidify urine, which could theoretically protect against UTIs. Patients received 500 mg of ascorbic acid four times daily versus a control group that took placebo pills. However, urine pH didn’t decrease with vitamin C supplementation, nor did the rate of UTIs go down. Therefore, even at such high doses, vitamin C failed to acidify patients’ urine or prevent recurring UTIs.

Vitamin C for UTI when pregnant

While it is still open for debate whether vitamin C could help pregnant women to prevent UTI, we know that ascorbic acid could be useful for fetus development. According to one study, “cardiac, hematologic and skeletal problems in fetuses can all be avoided” when the pregnant mammal ingests ascorbic acid as shown in animal models.

In another trial of more than a hundred pregnant woman, the participants were instructed to take 100 mg ascorbic acid (vitamin C) daily for three months.

The control group had twice as many positive cultures (> 1 x10^5CFU/ml) compared to the group of women who were taking ascorbic acid daily. The results allowed the researchers to conclude that ascorbic acid can help prevent UTIs.

However, the urine cultures were obtained three times per month at a pre-scheduled time, and the study did not specify how many women experienced UTI symptoms on top of the positive cultures.

Moreover, when I reached out to the researchers, they were unable to comment on whether or not the women included in the study have had recurrent UTIs prior to the study and if the women with abnormal cultures were reintroduced in the study after the treatment. Without this information, it’s difficult to further evaluate the study’s claim.  

In fact, the researchers speculated that perhaps pregnant women experience a deficit of vitamin C rather than suggesting that vitamin C can provide a protective action for a non-pregnant female.”The observed benefit from additional ascorbic acid intake leads us to believe that perhaps gestating women do not regularly receive ascorbic acid in their diets, or if they do, the quantities are insufficient, as has previously been reported”. Therefore, the study suggests a systemic effect of vitamin C supplementation rather than a direct effect on the bladder or urine.

The ascorbic acid dosage for UTI

There are many clinical studies that looked at ascorbic acid supplementation for a variety of health issues. In some studies, the patients took as much as 2 g of ascorbic acid daily. No adverse effects have been reported with doses up to 1,000 mg daily (1 g).

However, it is also established that “daily vitamin C intakes of 100–200 mg produce near saturation of plasma and tissues”. This means that when you go above this dosage, the rest is excreted in urine as waste.

At the same time, even larger doses of ascorbic acid (up to 1.8 g daily) do not reliably acidify the urine, as some studies show.

Therefore, the maximum absorption of ascorbic acid happens between 100-200 mg taken daily and the rest is flushed down the toilet without having any effect on urine. In this case, how do we expect vitamin C to help prevent UTIs?

A study discussed below shines the light on the complex circumstances in which vitamin C in the form of ascorbic acid could help prevent or even treat an acute UTI.

Vitamin C for UTI treatment

Before we analyze the findings of a study–“In Vitro Evaluation of a New Treatment for Urinary Tract Infections Caused by Nitrate-Reducing Bacteria”–that demonstrates how ascorbic acid could be helpful in fighting UTIs, let’s go over some chemistry.

If you are a UTI “frequent flyer”, you must have heard about nitrites in urine. Nitrites (not to be mistaken with nitrates) are a byproduct of certain bacterial activity. And when nitrites are further converted into nitrogen oxide, then and only then can ascorbic acid help eliminate pathogens, as a laboratory experiment demonstrated.

Therefore, this is what the study suggests:

  • Nitrates are normally present in your urine, as they are just a metabolite of food that you regularly consume.
  • Some bacteria produce an enzyme that changes urinary nitrates to nitrites (that’s why the presence of nitrites in the urine is an indirect indication of urinary tract infection).
  • At a low pH (acidic urine), nitrite is converted to a variety of nitrogen oxides (or “NO” on the chart of elements) that are toxic to bacteria.
  • In a lab experiment, ascorbic acid greatly increases the level of production of those nitrogen oxides (NO) from nitrite having a bacteriostatic effect in the urine comparable to antibiotics (trimethoprim, nitrofurantoin) tested in this model. So the pathogenic bacteria are killed with NO, and the more NO is released rapidly, the better the antibacterial effects. Therefore, ascorbic acid is merely a catalyst rather than an active ingredient.

As the study suggests: “The growth of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus saprophyticus was markedly reduced by the addition of nitrite to acidified urine. This inhibition was enhanced by ascorbic acid. In conclusion, we show that the growth of three common urinary pathogens is markedly inhibited in mildly acidified urine when nitrite is present.”

Crucial factors for ascorbic acid to work

Still, does it mean that ascorbic acid is as effective as antibiotics? Or maybe you could ditch your prescription altogether and use vitamin C instead to treat a UTI? Unfortunately, lab experiments are often different than real life.

As the researchers point out, when attempting to treat a UTI with vitamin C, several factors are key to success: timing, type of the bacteria, and urine pH management. Here is a list of these factors in more detail:

  • First, the approach only works if you have enough nitrates in your urine, to begin with.
  • Second, if nitrates are reduced to nitrites too slowly, bacteria will have time to adapt and survive. The process has to be very quick (which is always a challenge in a living organism).
  • Third, if bacteria are exposed to a combination of low pH, ascorbic acid, and nitrate from the start of the experiment, no effect on growth was observed. Meaning, the starting urine pH should be alkaline and there should be no ascorbic acid in it!
  • Moreover, this approach might only work if you have a nitrite-reducing bacteria, such as Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus saprophyticus. At the same time, a UTI could be caused by a variety of bacteria and their endless combinations.
  • It is likely that the antimicrobial activity of acidified nitrite in urine will vary because of the different compositions of urine, e.g., in relation to diet.
  • Infected urine often has a higher pH, and therefore, acidification is probably more difficult.
  • Unfortunately, only ammonium chloride in daily doses of 1.5 and 3 g has statistically been proven to acidify urine. And it’s not available over the counter.

So how would you go about using ascorbic acid for UTI treatment in a living organism, rather than in a lab? Let’s see how the process discussed in the study could theoretically be implemented in a living and breathing human body.

How to use ascorbic acid to kill UTI bacteria

As we discussed above, it has already been established that vitamin C doesn’t exert a protective effect by acidifying the urine (lowering the pH). Simply put, its’ urine acidification properties have not been reliably demonstrated. The bacteriostatic effect of acidified nitrite is likely related to the release of NO and other toxic reactive nitrogen intermediates.

Let’s now review the findings of the study, keeping in mind that the process was demonstrated in a lab and hasn’t been replicated in humans:

For this approach to work, you have to have alkaline urine (the optimum pH is about 8) and you cannot have taken ascorbic acid as a preventive measure. If these conditions are met, theoretically you can attempt the following:

Step one: Increase the number of nitrates by ingesting sodium nitrate (10 mg/kg) or consuming approx. 300 gr of spinach.

Step two: An hour later, acidify your urine and take ascorbic acid as well. Just to remind you: ascorbic acid on its own won’t acidify your urine, it can only increase the release of nitrogen oxides that, in turn, could kill the bacteria.

  1. a) Theoretically, one can take ammonium chloride to rapidly acidify the urine. Use of ammonium chloride has been clinically shown to reduce urine pH relatively quickly. One would need to acidify urine to achieve urinary pHs between 4.6 and 5.5 for this approach to work. The study authors point out that “even if the pH can be sufficiently lowered, it will likely be important that this process be rather rapid so that bacteria will not have time to up-regulate defense mechanisms.”
  2. b) At the same time, drink 1-2 grams of ascorbic acid.

As you can see, it’s not straightforward, there are lots of caveats, and it’s unclear if this process, achieved in a lab, could be repeated in a patient. There also could be serious health side-effects when consuming any of the listed substances for the purposes of modulating urine pH.

Vitamin C or cranberry for UTI?

While cranberries contain vitamin C, this isn’t believed to be the reason why they prevent UTIs.  No one knows the exact mechanism of action of cranberry juice in the prevention of UTIs but it is believed to interfere with the adherence of bacteria to the inner lining of the bladder. Early studies didn’t standardize the number of protective proanthocyanidins (PACs) in the cranberry supplements.  It’s the PACs that appear to exert the greatest effect on UTIs.

Recently, new, more concentrated supplements have been appearing on the market that have achieved better results in preventing UTIs than cranberry juice or your regular cranberry pills.

A review study on cranberry juice in 2008 concluded that cranberry juice did reduce the incidence of recurrent UTIs; however, more recent reviews have shown no significant reduction in symptomatic, recurrent UTIs. While the protective effect of cranberry juice is equivocal, it doesn’t cause antibiotic resistances like low-dose antibiotics do and may work to prevent UTIs to a limited degree.

A little-used preventive against UTIs is D-mannose. In animal studies, it has been shown to block the adhesion of pathogenic bacteria to the cells lining the bladder.  A recent study (8) looked at giving 2 grams daily of D-mannose for six months. Other subjects took antibiotic (nitrofurantoin) prophylaxis or nothing. The incidence of recurrent UTI in the group taking D-mannose was just 15 percent versus 20 percent in the antibiotic prophylaxis group. Those that took nothing had a 60 percent incidence of UTI.

The Bottom Line

Many women with recurrent UTIs are on the search for something other than antibiotic prophylaxis to prevent UTIs. Vitamin C has been suggested and is used widely even though the research, isn’t very positive about its effectiveness. It doesn’t acidify the urine as was once thought and it didn’t prevent recurrent UTIs in all studies. Many of the studies have been poorly-designed, so it is difficult to really interpret the results. On the other hand, vitamin C/ascorbic acid is inexpensive and most studies have used just 100 mg per day. In fact, even the placebo helps patients, so if you believe that vitamin C works for you, it is completely safe to take.

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