I fight practically every day for this cause.
I am going to present a study by the infectious disease specialist Manisha Juthani-Mehta of the Yale School of Medicine who studied the effects of daily high-dose cranberry capsules – the equivalent of 600 ml of juice (huge dosage and sugars!) – over 185 women of a nursing home.
A little preamble. About 60% of women will experience an urinary tract infection during their lifetime.
For many years, some doctors have recommended the use of cranberry juice and dry extract tablets as a way to prevent recurrent UTIs (urinary tract infections) or to treat symptoms.
With a huge surprise, in this study they found no difference between people treated with cranberry or placebo.
In fact, if we look at all the scientific literature on the subject, it turns out that the recommended amount of daily cranberry juice goes far beyond a possible and realistic dose for a human being.
Women chosen as sample for the study are elderly women living in a nursing home (UI are the most commonly diagnosed infections).
About half of the women living in nursing homes have bacteriuria (bacteria in the urine) and 90% have pyuria (presence of bacteria and white blood cells in the urine). These two symptoms are indicative of the presence of bacteria.
The participants were divided into two groups to which they were assigned random:
- two cranberry capsules per day, each with 36 milligrams of proanthocyanidin (active ingredient)
Before starting the study, 31% of the participants had bacteriuria and pyuria in the urine.
After 360 days (one year!) of placebo or cranberry capsules, the participants bacteriuria and pyuria levels were checked again.
Researchers found no differences in the presence of bacteriuria plus pyuria from the cranberry group and the placebo one. They also found no differences in the number of UTI episodes (38 women did not complete the study because they could not take the product or left the study for unrelated reasons, so the results are based on the 147 remaining participants).
Therefore, the study established the ineffectiveness of the use of cranberry in UIs.
The continuous promotion of the use of cranberry to prevent recurrent urinary infections is inconsistent compared to repeated studies.
Any continued promotion of the use of cranberry products seems to go beyond scientific evidence.
A review of 2012 literature of 24 studies with a total of 4,473 participants found little evidence on positive effects and concluded that cranberry juice and its extracts cannot be recommended for the prevention of urinary tract infections.
Since cranberry juice normally contains 27% of squeezed fruit, it is logical that something so diluted is not effective. Still, according to the results of this recent study, even if we increase the dose, there are no visible positive effects.
Why did this myth hold for so long?
There are a couple of reasons: first, it has been shown that the active ingredient of cranberries, proanthocyanidins type A (PAC), blocks the adhesion of bacteria on the bladder wall.
So, a reasonable hypothesis is that, if bacteria cause an UI, something that prevents them from accumulating in the bladder, could be a potential remedy or a preventive measure.
We know that for an UTI to occur, bacteria must adhere and invade the lining of the bladder. PACs interfere with the ability of bacteria to attach to the bladder “wall” and create an infection.
But there is a problem.
An extremely high concentration of cranberries is needed to provide the dose of proanthocyanidins to prevent bacterial adhesion. This amount is not found in the juices we drink or in the food supplements we take.
So now we have evidence that the concentration of PAC of the tablets is not strong enough to prevent bacteria accumulation in the bladder.
The second reason why this myth is so difficult to die is that it is such a beautiful myth to believe in. If you have ever had a recurring urinary tract infection and wished to prevent it or wanted to feel more beneficial while waiting for antibiotics to take action, drinking cranberry juice or taking capsules is a simple way to feel like you are helping your body.
However, at best, you are wasting a lot of money for something that does the same job as a glass of water. I underline that cranberry contains many sugars and, in those concentrations, glycemic peaks and other disadvantages are behind the corner.
There are other substances, much more active than proanthocyanidins that guarantee an inhibitory action of bacterial adhesiveness (especially D-Mannose) and, in addition, without the side effects and contraindications of cranberries.
Be clear, cranberry (in all its varieties: cranberry, blackberry, Canadian, American, etc.) is an excellent ally for eyes, microcirculation functionality and is a good antioxidant, but if you have an UI, cranberry is not necessary.
It is better to rely on the action of D-Mannose that has no side effects and whose effectiveness is demonstrated by dozens of studies.
I also recommend to stay hydrated with water (without gas) and to avoid irritating foods such as pepper, tomatoes, spices and coffee.
The study was published in the Journal of the American Medical Association and can be found here: