Cranberry is a widely cultivated plant, with the majority of the crop processed into juice, sauce or dried and sweetened. Cranberry sauce is regarded indispensable in American and Canadian Thanksgiving dishes, but recently it has become a lot more popular, thanks to its high antioxidant capacity and microbe fighting properties. Cranberries are a good source of polyphenol antioxidants, anthocyanidin flavonoids, cyanidin, peonidin and quercetin.

Cranberries have garnered a lot of attention because they appear to be effective against urinary tract infections (UTIs). At first these effects were attributed to acidification of urine, but newer research suggests this effect is due to proanthocyanadins and tanins, which make it harder for bacteria to adhere to the epithelial cells of the bladder and urethra.

In a recent trial, drinking cranberry products significantly reduced the incidence of UTIs over a 12 month period by 39% compared to the placebo group. Reduction was only seen among women while it remains unclear whether cranberries have the same effect in children and elderly men and women.

Cranberries appear to be effective in the prevention the recurrence of UTIs, but it is unclear weather they could be used as a substitute for antibiotics in the treatment of urinary tract infections. A common treatment for prevention of UTI recurrence are prophylactic antibiotics, but in this case, the development of antimicrobial resistance is a major concern. Unfortunately, thus far, there have not been any head-to-head studies comparing the efficacy of cranberry products with prophylactic antibiotics.

Cranberries can be consumed as different products -- either as a juice or concentrate or as capsules or tablets or as dried berries. In trials, there was no significant difference in the incidence of UTIs between juice and capsules, so the optimum method of administration remains uncertain.

Drinking cranberry juice is not associated with any significant adverse effects, even with prolonged use. Some sources report cranberry juice is safe in amounts as high as 4 L per day in healthy adults, while others state that quantities of 3 L or more may cause gastrointestinal distress, including diarrhoea in adults. Hypersensitivity and diarrhoea were reported amongst children if the intake exceeded 300 mL per day.

Safe and recommended doses are:

• 90 to 480 mL of cranberry cocktail twice daily
• 15 to 30 mL of unsweetened 100% cranberry juice daily
• 30 to 45 mL of cranberry concentrate twice daily (30 times stronger than the juice)
• 1 to 6 capsules of 300 to 400 mg concentrated extract twice daily

Patients on warfarin (anticoagulant) should be extra cautious if consuming cranberries, as there have been several reports of increased risk of bleeding with this combination. In addition, patients with a history of kidney stones should avoid using cranberry juice or products, since they might increase calcium and oxalate concentrations and therefore accelerate renal stone formation. People with diabetes need to avoid cranberry juices sweetened with fructose.

Many other beneficial effects have also been attributed to cranberries, but most of them are not yet confirmed. This includes reducing the risk for breast cancer and atherosclerosis, antiviral, antifungal and antibacterial activity (including the infamous Helicobacter pylori that causes stomach ulcers and Streptococcus mutans, a leading cause of tooth decay). It appears that cranberries might have a much broader range of benefits than was originally thought.

Sources: Cranberries and Urinary Tract Infections (Medscape), Cranberries May Fight Cavities (Medscape), Potential Additional Health Benefits of Cranberries (Medscape), Cranberries for preventing urinary tract infections (Medscape), Cranberry (Wikipedia).