Urinary tract infections (UTIs) are common with women about 30 times more likely to develop one than men. The bacterial infection of a UTI can cause painful burning sensations when urinating, frequent and strong urges to urinate, and changes in the composition of the urine. Antibiotics are the most common first-line treatment for UTIs, but there is growing interest in the role that nutrition-related treatments can play in reducing the risk of developing a UTI in the first place. Enter the most common self-prescribed and best-researched treatment: the humble cranberry. In this podcast, I’ll look at the evidence for cranberries in all their forms for helping to reduce the risk of developing UTIs.
Urinary tract infections are very common with one in two women experiencing at least one in their lifetime. Contrast that to men where the rate is around 1 in 20. So what explains this difference?
UTIs are caused when bacteria enter the body through the urethra and colonise the urinary tract. Because the urethra is much shorter and straighter in females than in males and the vagina is closer to the anus where there are lots of bacteria, then there are many more opportunities for infection to happen in women compared to men. Add to this hormonal changes during pregnancy and menopause which can also increase the likelihood of a UTI in women.
A UTI can be seen in any part of the urinary system with the bladder being the most common site, but it also can occur in the urethra and kidneys. Some of the signs and symptoms of a UTI include passing very small amounts of urine, experiencing the need to pass urine frequently, having stinging or burning pain when urinating and passing cloudy, bloody or smelly urine. This makes UTIs one of the most common medical conditions requiring inpatient or outpatient treatment.
UTIs can be classified as uncomplicated and complicated. Uncomplicated UTIs are localised to the bladder and is where the infection and inflammation sits. Complicated UTIs are where infection spreads from the bladder to the kidneys or other parts of the urinary system and can present with more serious symptoms like fever, back pain and vomiting.
Uncomplicated UTIs can usually resolve without treatment in healthy, nonpregnant women. Often, UTIs are treated with antibiotics to treat the underlying bacterial infection cause.
With UTIs being so common in women, there is a lot of interest in how someone could help to lower the risk of developing them and potentially even treat uncomplicated UTIs. This is where a range of natural treatments have been promoted and these include staying well hydrated, probiotics to help compete out the invading bacteria, vitamin C (which is used to acidify the urine), taking D-mannose which is a sugar that may help prevent certain bacteria from sticking to the urinary tract walls, and then of course, one of the most popular: cranberries.
Cranberries contain compounds called proanthocyanidins that are thought to help lower the risk of UTIs. Proanthocyanidins are polyphenol compounds that give many fruits, especially berries, their vibrant red, blue and purple colours.
When bacteria like E. coli attach to the urinary tract walls, they can multiply and cause an infection. The proanthocyanidins in cranberries can interfere with the bacteria's ability to stick to the urinary tract lining, making it more difficult for them to colonise and cause an infection.
Also, cranberries have a mildly acidic property that may create an unfavourable environment for bacteria to thrive. This acidity can help inhibit the growth and survival of bacteria in the urinary tract.
So there is plenty of theory, but what does the research say? This is one area where there are plenty of clinical trials to draw upon that can be combined into a systematic review. And the research has been analysed as part of a Cochrane Review – considered one of the highest standards of research evidence.
This wasn’t the first review on the topic of cranberries and UTIs, but in fact, the fifth update since the evidence was first assessed way back in 1998 – so there has been plenty of research in the intervening years to take into account.
The review analysed the results of randomised controlled trials which compared the occurrence of UTIs in people taking a cranberry product for a minimum of 1 month compared to those taking a placebo or no treatment. They also took it a step further and analysed studies that compared a cranberry product against other popular treatments such as antibiotics or probiotics.
In all, 50 randomised trials were included in the review that involved over 8,800 people. It included a mix of participants such as women with a history of recurrent UTIs, women who were pregnant, institutionalised older adults, people undergoing medical or surgical interventions that increase the risk of UTIs, adults with bladder-emptying issues, and children.
The primary outcome was the number of people in each group with symptomatic UTIs as verified by laboratory culture of bacteria. And I’ll link to the systematic review in the show notes. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD001321.pub6/full
Let’s dive into what the review found. The headline finding was that taking cranberries as a juice, tablet or capsule reduced the risk of developing UTIs by 30 percent. But the benefit wasn’t equal. The greatest benefit was seen in women with recurrent UTIs, children with UTIs, and in people susceptible to UTIs following an intervention such as bladder radiotherapy.
For elderly institutionalised men and women, adults with neuromuscular bladder dysfunction and incomplete bladder emptying, or in women who were pregnant there was no benefit seen. But the number of studies in these groups was small leading the research team to state the estimates here are uncertain.
When looking at a comparison of cranberry products versus antibiotics or probiotics there weren’t many high-quality studies to make a clear conclusion although it suggested that there was some promise with cranberry products being more effective when compared to probiotics, but there were only three studies to make this judgement on.
Over half of the studies were considered to have robust study design and to be free from significant sources of bias.
And while there were studies that had involvement to some level from a commercial organisation, these studies did not report any different results from those studies with no commercial involvement.
The review was unable to give clear guidance on what the optimal dose of cranberry should be and by ‘dose’ here, I’m referring to the proanthocyanidins and which the levels can be variable between different cranberry formulations.
So, let’s wrap all this up. Based on the findings of the latest Cochrane Review, there is evidence to support the use of cranberry products either as juice, tablets or powder to reduce the risk of developing UTIs – most notably in women with recurrent UTIs, in children, and in people susceptible to UTIs following interventions.
I need to add a disclaimer to finish off though that it is important to seek medical attention if you think you have a UTI rather than just self-treat with a glass of cranberry juice. This is especially important if you think you may have a bladder or kidney infection, both of which are very serious conditions. UTIs can be more dangerous if you’re pregnant due to an increased risk of kidney involvement so please see your doctor if you are pregnant and you think you have a UTI, even if your symptoms are mild.
So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.
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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.