Cranberry and cancer

Summary on Cranberry

Action:

When eating or drinking cranberries, natural compounds are released that prevent bacteria from sticking to the bladder, which counteracts bladder infections. The berries simultaneously deliver strong antioxidants and reduce inflammation in body tissues.

Potential in cancer:

Laboratory studies show that compounds in cranberries can slow down the ability of cancer cells to divide and help initiate the natural suicide mechanism of cancer cells. They are also being investigated for whether they can make cancer cells more susceptible to chemotherapy.

Main limitation:

Cranberries can enhance the effect of the blood-thinning medication Warfarin (Marevan), which increases the risk of bleeding. The berries also contain substances that can increase the risk of kidney stones, and many finished cranberry products contain large amounts of added sugar.

What is Cranberry

Cranberry (specifically Vaccinium macrocarpon, the American large cranberry) is a small, hardy, red berry belonging to the heather family. The berry is known for its characteristically very tart and slightly bitter taste, which is due to its low sugar content and high content of organic acids.

Cranberries grow wild in peat bogs and on acidic soils in cooler climates, primarily in North America. Their health value is attributed to a rich content of bioactive substances, especially polyphenols. The most unique and studied of these are A-type proanthocyanidins (PACs), which differ from the B-type PACs found in most other fruits. In addition, the berries contain anthocyanins (which give the red color), flavonoids such as quercetin and myricetin, as well as ursolic acid and vitamin C.

History

Indigenous peoples in North America, such as the Algonquin tribes, have used cranberries for centuries, long before European settlers arrived. They used the berries as an important food source (often mixed with meat and fat), as a dye for textiles, and as medicine. Medicinally, the crushed berries were used to treat wounds (as a poultice to draw out poison) and to relieve ailments related to the urinary tract.

European settlers adopted the use and began cultivating the berries commercially starting in the early 1800s. Modern scientific interest began in earnest in the 20th century, when researchers started to understand their specific ability to prevent urinary tract infections.

Mechanisms of action

The biological effects of cranberries are complex and are attributed to an interplay between the many active substances.

Anti-adhesion (A-type PACs)

This is the most well-known mechanism of cranberries. The A-type proanthocyanidins have a unique structure that enables them to block the adhesion molecules (fimbriae) that bacteria use to stick to mucous membranes.

Primary research has focused on Escherichia coli (E. coli), which causes most urinary tract infections (UTIs). By preventing E. coli from binding to the bladder wall, the bacteria are flushed out with the urine before an infection can become established. This mechanism has also been observed in relation to Helicobacter pylori, a bacterium that can cause stomach ulcers and is a risk factor for stomach cancer, where PACs can inhibit its binding to the gastric mucosa.

Anti-inflammatory properties

Chronic inflammation is a known risk factor for the development and progression of cancer. The polyphenols in cranberries have been shown to interfere with inflammatory processes. They can inhibit the activity of central signaling pathways, such as NF-κB, which acts as a “master switch” for inflammation. They can also reduce the production of pro-inflammatory enzymes (such as COX-2) and signaling molecules (cytokines). [3]

Antioxidant capacity

Cranberries have a high content of antioxidants, including vitamin C, anthocyanins, and flavonoids. These substances neutralize free radicals – unstable molecules formed as a byproduct of the body’s metabolism and through external influences (e.g., radiation and chemotherapy). Free radicals can cause oxidative stress, leading to damage to cell DNA, proteins, and fats. By protecting DNA from damage, antioxidants can help prevent the mutations that can lead to cancer.

Modulation of gut microbiota

A significant portion of cranberry polyphenols, especially PACs, is not absorbed in the upper gastrointestinal tract. Instead, they reach the colon, where they interact with the gut flora. Here, they function as prebiotics – food for beneficial bacteria such as Akkermansia muciniphila and Bifidobacterium. This promotes a healthier gut flora, which is essential for a well-functioning immune system. Furthermore, bacteria break down these substances into short-chain fatty acids (SCFAs), such as butyrate, which is vital for colonic mucosal health and possesses anti-cancer properties in the gut.

Influence on cell signaling

Substances in cranberries, including ursolic acid and PACs, have demonstrated the ability in in vitro (in a test tube/petri dish) studies to disrupt the signaling pathways that cancer cells depend on to grow and divide uncontrollably. This includes the inhibition of signaling pathways such as PI3K/Akt/mTOR and MAPK, which are often overactive in cancer cells. By blocking these signals, cranberry compounds can slow down cell growth. [2]

Potential in cancer

It is important to emphasize that cranberry is not a treatment for cancer, but that preclinical research (studies in cells and animals) has shown a number of interesting mechanisms that make the berry relevant as complementary support.

Inhibition of cell growth and apoptosis

Several in vitro studies have shown that cranberry extract can inhibit proliferation (cell division) in cancer cell lines from, among others, breast, prostate, colon, ovarian, and lung cancer. Even more importantly, the extracts have been shown to induce apoptosis (programmed cell death). Cancer cells have typically lost the ability to undergo apoptosis, but substances in cranberries appear to be able to “reboot” this program, causing the cancer cells to destroy themselves.

Anti-angiogenesis

For a tumor to grow larger than a few millimeters, it depends on forming new blood vessels to deliver oxygen and nutrients. This process is called angiogenesis. Preclinical studies suggest that polyphenols from cranberries can inhibit the signals that the tumor sends out to attract new blood vessels, potentially “starving” the tumor and slowing its growth.

Synergy with chemotherapy

Some of the most promising research focuses on the potential of cranberries to act in synergy with conventional treatment. In vitro studies have shown that the addition of cranberry extract can make resistant cancer cells more sensitive to specific types of chemotherapy. This phenomenon, known as chemosensitization, could theoretically mean that treatment works better, or that lower doses can be used, thereby reducing side effects. [5]

Advantages of Cranberry

In addition to the direct anti-cancer mechanisms, cranberries offer a variety of other health benefits that may be relevant.

Prevention of urinary tract infections (UTIs)

This is the most well-documented benefit of cranberries. The ability to prevent E. coli from sticking to the bladder has been clinically studied. For cancer patients who may be immunocompromised, have a urinary catheter, or undergo treatments that increase the risk of infections, the prevention of UTIs can be a significant advantage.

Cardiovascular health

The polyphenols in cranberries have shown positive effects on the cardiovascular system. Studies indicate that they can contribute to lowering “bad” LDL cholesterol and raising “good” HDL cholesterol. They can also improve endothelial function (the health of the innermost layer of blood vessels) and help lower blood pressure, all of which reduce stress on the heart. [1]

Oral health

The same anti-adhesive mechanism that works in the bladder also works in the mouth. PACs can prevent plaque-forming bacteria from binding to teeth, which can reduce the risk of cavities (caries) and gum disease.

Stomach health

As mentioned, cranberries can inhibit the binding of Helicobacter pylori to the gastric mucosa. This can potentially reduce the risk of stomach ulcers and the chronic inflammation caused by this bacterium.

Disadvantages and limitations

Although cranberries are generally safe, there are limitations and conditions to keep in mind.

Sugar content in commercial products

Fresh cranberries are extremely tart. To make cranberry juice and dried cranberries palatable, large amounts of sugar or other sweeteners are often added. High sugar intake is undesirable, as it promotes inflammation and can fuel cancer cells. It is therefore crucial to choose unsweetened juice or standardized extracts in capsule form.

Risk of kidney stones

Cranberries are rich in oxalates (oxalic acid). In individuals with a history of or a tendency to form calcium oxalate kidney stones (the most common type), a high and sustained intake of cranberries can increase the risk of stone formation.

Gastrointestinal discomfort

Ingesting very large quantities of cranberries, especially concentrated juice or extract, can lead to gastrointestinal issues such as bloating, stomach cramps, and diarrhea in sensitive individuals.

Bioavailability

A significant limitation in the research is that many of the beneficial polyphenols have low bioavailability, meaning they are poorly absorbed from the gut into the bloodstream. The concentrations that show effects in vitro can be difficult to achieve within the body. However, their effect within the gut itself (on the microbiome) does not depend on absorption.

Clinical studies

It is important to distinguish between the different types of research. The vast majority of research on cranberries and cancer is preclinical, meaning in vitro (in a test tube/petri dish) and in vivo (in living organisms, typically mice). These studies are crucial for understanding mechanisms but cannot be directly translated to humans.

There is a lack of large, randomized clinical trials investigating cranberry as a direct complementary treatment for cancer. The clinical studies available in humans have primarily focused on the role of cranberries in preventing UTIs (urinary tract infections), where the evidence is relatively strong, as well as on markers of cardiovascular health.

Safety

Cranberries in the form of food (berries and unsweetened juice) are considered very safe for most people. As a supplement in high doses, there are a few precautions.

Interaction with blood-thinning medication

The most clinically relevant interaction is with Warfarin (Marevan). There are several reports and studies indicating that cranberries (especially in large amounts or as a concentrated product) can inhibit the breakdown of Warfarin in the body. This intensifies the drug’s effect and increases the INR value (blood clotting time), resulting in a significant risk of serious bleeding. Individuals undergoing treatment with Warfarin must discuss any intake of cranberry products with their practitioner. [4]

Interaction with other medications

Cranberry components can theoretically affect the liver’s CYP450 enzyme system, which is responsible for breaking down a wide variety of medications (including chemotherapy). However, the evidence is mixed and not as strong as with Warfarin. As a precaution, one should inform their practitioner if beginning a regular intake of high-dose cranberry supplements alongside other vital medication.

Dispensing and application

Cranberries can be consumed in several ways, and the choice depends on the purpose.

Fresh or frozen berries: The most natural form with all compounds intact. They are very tart and are typically used in cooking or smoothies.
Unsweetened cranberry juice (concentrate): A good source of active substances, but the taste is intense. It must be diluted and must not contain added sugar.
Capsules/tablets (extract): This is the easiest way to get a standardized and high dose of the active substances, especially PACs, without consuming sugar or being bothered by the tart taste.
Dried cranberries: A popular snack, but one must pay close attention to the ingredient list, as they are almost always altered with large amounts of added sugar and oil.
Powder: Dried and powdered cranberry that can be mixed into liquids or food.

For the prevention of UTIs, doses delivering at least 36 mg of PACs daily are often recommended. The dosage in connection with complementary cancer treatment has not been established due to a lack of clinical studies.

Conclusion

Cranberry is a berry with a strong health profile, backed by a long history and a growing body of scientific research. Its primary, well-documented strength lies in the prevention of urinary tract infections via the anti-adhesive properties of A-type PACs.

Preclinical research into the potential of cranberries in cancer is promising. The mechanisms, which involve anti-inflammation, antioxidant protection, inhibition of cell growth, and induction of apoptosis, suggest that the berry can be a valuable part of a supportive diet.

While it cannot replace conventional treatment, a cranberry supplement (especially sugar-free extract) can be a safe and beneficial addition for most people, provided that the serious interaction with Warfarin and the risk of kidney stones are taken into account.

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