health benefits of cranberry

What is cranberry

Cranberries are a group of evergreen dwarf shrubs in the subgenus Oxycoccus of the genus Vaccinium 1). In Britain, cranberry may refer to the native species Vaccinium oxycoccos 2), while in North America, cranberry may refer to Vaccinium macrocarpon 3). Vaccinium oxycoccos is cultivated in central and northern Europe, while Vaccinium macrocarpon is cultivated throughout the northern United States, Canada and Chile 4). In some methods of classification, Oxycoccus is regarded as a genus in its own right. They can be found in acidic bogs throughout the cooler regions of the northern hemisphere.

Cranberry is a native evergreen shrub that grows throughout North America. Historically, cranberry fruits or leaves were used for bladder, stomach, and liver disorders, as well as diabetes, wounds, and other conditions. Today, cranberry is used as a dietary supplement primarily for urinary tract infections (UTIs). It has also been used for oral and gastrointestinal infections, cardiovascular diseases, and against cancer. The berries are used in beverages and food. They are also made into dietary supplements in the form of extracts, powder, capsules, and tablets. Cranberry juice extracts and constituents exhibit antibacterial 5), antimicrobial 6), antifungal 7), anti-inflammatory 8), antioxidant 9), and antiadherence 10) properties.

As fresh cranberries are hard and bitter, about 95% of cranberries are processed and used to make cranberry juice and sauce. They are also sold dried and sweetened 11).

Cranberry juice is usually sweetened or blended with other fruit juices to reduce its natural tartness. Many cocktails, including the Cosmopolitan, are made with cranberry juice. At one teaspoon of sugar per ounce, cranberry juice cocktail is more highly sweetened than even soda drinks that have been linked to obesity.

Usually cranberries as fruit are cooked into a compote or jelly, known as cranberry sauce. Such preparations are traditionally served with roast turkey, as a staple of English Christmas dinners, and Thanksgiving (both in Canada and in the United States). The berry is also used in baking (muffins, scones, cakes and breads). In baking it is often combined with orange or orange zest. Less commonly, cranberries are used to add tartness to savory dishes such as soups and stews.

Fresh cranberries can be frozen at home, and will keep up to nine months; they can be used directly in recipes without thawing 12).

Cranberry harvest

The cranberry is a Native American wetland fruit which grows on trailing vines like a strawberry. The vines thrive on the special combination of soils and water properties found in wetlands 13). Wetlands are nature’s sponges; they store and purify water and help to maintain the water table. Cranberries grow in beds layered with sand, peat and gravel. These beds are commonly known as bogs or marshes and were originally formed as a result of glacial deposits.

In Massachusetts, the place where cranberries grow is called a bog. Natural bogs evolved from deposits left by the glaciers more than 10,000 years ago. These deposits were left in impermeable kettle holes lined with clay. The clay prevents materials from leaching into the groundwater. Rocks and other organic materials were collected by the glaciers. When the ice finally melted deposits of heavy materials were layered on top of the clay.

These kettle holes were filled with water and organic matter which created the ideal environment for cranberries. Today, growers spread a inch or two of sand on their bogs every three years. The sand not only helps the vines grow but also slows the growth of weeds and insects. Normally, growers do not replant each year since an undamaged cranberry vine will survive indefinitely. Some vines on Cape Cod are more than 150 years old and are still bearing fruit.

Cranberries are harvested in the fall when the fruit takes on its distinctive deep red color. Berries that receive sun turn a deep red when fully ripe, while those that do not fully mature are a pale pink or white color. This is usually in September through the first part of November. To harvest cranberries, the beds are flooded with six to eight inches (15 to 20 centimeters) of water above the vines. A harvester is driven through the beds to remove the fruit from the vines. For the past 50 years, water reel type harvesters have been used. Harvested cranberries float in the water and can be corralled into a corner of the bed and conveyed or pumped from the bed. From the farm, cranberries are taken to receiving stations where they are cleaned, sorted, and stored prior to packaging or processing.

Although most cranberries are wet-picked as described above, 5–10% of the US crop is still dry-picked.

Dry harvested cranberries represent the fruit that is sold as fresh fruit at farmer’s markets, road-side stands and grocery store shelves. This traditional method of harvesting now represents about 10% of the Massachusetts cranberry harvest. The other 90% of the crop is picked wet and is used to make juice, sauce, sweetened dried cranberries, among other products. Even though fresh fruit represents a small fraction of the total harvested crop, it nevertheless is an important aspect of the cranberry industry and for many growers, a way of life.

In order to pick the fresh fruit, the vines must be completely dry. Even a slight shower the night before, heavy dew, or damp conditions from a frost night is enough to delay harvest until the conditions improve on the bog. Depending on the harvest season, these conditions can provide more than enough challenges to growers. This entails higher labor costs and lower yield, but dry-picked berries are less bruised and can be sold as fresh fruit instead of having to be immediately frozen or processed.

Originally performed with two-handed comb scoops, dry picking is today accomplished by motorized, walk-behind harvesters with styles named Darlington, Furford or Western, which must be small enough to traverse beds without damaging the vines. These self-propelled harvesters all work in a similar manner, combing through the bogs and the fruit is then conveyed into a burlap bag or wooden box. In previous generations, wooden boxes were the collection device of choice but today most growers utilize burlap. Once the bag is full, the operator stops the machine, removes the bag and sets it on the bog, places an empty bag onto the machine and continues harvesting. After a sufficient amount of bags have been filled, the bags are then generally transported into larger containers. Some growers carry the bags off of the bog by hand, some by tractors with trailers, while others empty the bags into large plastic bins that can hold about 300 pounds of fruit. They they stack two more bins on top of the original bin, filling each bin as they proceed. The stack of three bins is then flown off of the bog via helicopter and onto waiting flatbed trucks for delivery to the screening plant or storage barn.

White cranberry juice is made from regular cranberries that have been harvested after the fruits are mature, but before they have attained their characteristic dark red color. Yields are lower on beds harvested early and the early flooding tends to damage vines, but not severely.

Cranberries for fresh market are stored in shallow bins or boxes with perforated or slatted bottoms, which deter decay by allowing air to circulate. Because harvest occurs in late autumn, cranberries for fresh market are frequently stored in thick walled barns without mechanical refrigeration. Temperatures are regulated by opening and closing vents in the barn as needed. Cranberries destined for processing are usually frozen in bulk containers shortly after arriving at a receiving station.

Cranberry nutrition facts

Raw cranberries have moderate levels of vitamin C, dietary fiber and the essential dietary mineral, manganese (each nutrient having more than 10% of the Daily Value per 100 g serving, as well as other essential micronutrients in minor amounts 14).

Table 1. Cranberries (raw) nutrition facts

[Source: United States Department of Agriculture Agricultural Research Service 15)]

Table 2. Phytochemical content of cranberry foods

Food sourceFlavan-3-ol monomers and dimers 16), 17)Proanthocyanidins 18), 19)Anthocyanins 20), 21)Hydroxybenzoic acids 22), 23)Hydroxycinnamic acids 24), 25)Terpenes 26)Flavonols 27)
Cranberry fruit
mg/100 g7–33133–36713–171503–60273–8265–12520–40
mg/serving15.6–26.4106–29310.4–136.8402–48257.6–65.652–10016–32
Cranberry juice
mg/L6–3589–23027–1326412–19Trace11–58
mg/serving2717.8–465.4–26.412.82.4–3.8Trace2.2–11.6
Canned cranberry sauce
mg/100 g112.816–54.40.6–11.847647.51.1–22.85
mg/serving378.911.2–380.4–8.3333.233.20.8–16
Sweetened, dried cranberries
mg/100 g64.210.398.5
mg/serving425.64.139.4
180 g whole fruit.
2200 mL juice.
370 g sauce.
440 g dried fruit.
5No data available.
[Source 28). The putative health benefits have recently emerged from study of Vaccinium species include cardioprotective effects 29), anticancer properties 30), and reversal of age-related motor behavioral deficits 31). The compounds responsible for this bioactivity have not been fully elucidated; however, the focus of research has centered on classes of polyphenols abundant in berries, especially anthocyanins 32). Cranberries contain appreciable quantities of anthocyanins 33). Studies of individual anthocyanins reveal their bioavailability to plasma is generally <1% of consumed quantities. Only recently have studies been conducted to determine tissue concentrations of anthocyanins 34) and their fate in the lower intestinal tract is unknown. Despite low bioavailability, plasma concentrations of anthocyanins appear sufficient to induce changes in signal transduction and gene expression in the body 35), 36) in a manner that suggests their putative role in physiological functions and health outcomes.

Cranberry juice is a rich source of polyphenolic compounds, particularly anthocyanins 37), 38). Investigators have proposed that cranberry consumption might have protective effects against cardiovascular disease by reducing inflammation and serum lipids 39), 40). However additional studies are needed to define the mechanisms and clinical implications of these vascular effects 41).

Epidemiologic studies have shown that consumption of flavonoid-containing foods and beverages is associated with reduced cardiovascular disease risk 42), 43). Whereas the mechanisms accounting for this benefit remain incompletely defined, clinical studies have identified many relevant effects. For example, consumption of grapes, cocoa, and other flavonoid-containing foods may reduce blood pressure 44), platelet aggregation 45), insulin resistance 46), and cholesterol concentrations 47). In test tube and biomarker studies suggest that such foods have anti-inflammatory effects 48). Recently, there has been particular interest in the possibility that flavonoids also reduce cardiovascular disease risk by reversing endothelial dysfunction.

Endothelial dysfunction is a key mechanism in the pathogenesis of atherosclerotic vascular disease 49). Risk factors decrease the bioavailability of endothelium-derived nitric oxide and induce a proinflammatory endothelial phenotype that promotes atherosclerosis and arterial stiffness. Risk-reduction therapies and lifestyle changes improve endothelial function 50). Prior studies have shown favorable effects of tea, cocoa, grape juice, and other dietary sources of flavonoids on endothelial function in patients with coronary disease and other risk factors 51).

Summary on cranberries and their bioactive constituents in human health

There is strong experimental evidence that cranberry bioactives have favorable effects on blood pressure, glucose metabolism, lipoprotein profiles, oxidative stress, inflammation, and endothelial function. However, the currently available data from human studies provide mixed results about the clinical significance of these actions on cardiovascular health. The evidence for in vivo effects on oxidative stress and inflammation is not convincing at this stage. Favorable effects on endothelial function appear to be limited to acute responses after consumption of cranberry juice or cranberry anthocyanins. One well-controlled study suggests a chronic benefit on carotid-femoral pulse wave velocity, which is emerging as an important measure of arterial function with relevance to the risk of coronary heart disease 52). Thus, there is encouraging, but limited, evidence of cardioprotective effects of cranberries.

Cranberry juice and urinary tract infection

There is some human evidence supporting the use of cranberry juice and cranberry supplements to prevent urinary tract infection (UTI), although most available studies are of lesser quality 53). Clear dosing guidelines are lacking, but given the safety of cranberry, it may be reasonable to recommend the use of moderate amounts of cranberry juice cocktail to prevent urinary tract infection (UTI) in non-chronically ill individuals.

  • Cranberry hasn’t been shown to be effective as a treatment for an existing urinary tract infection 54).
  • And cranberry juice may be unacceptable to consume in the long term. Cranberry products (such as tablets or capsules) were also ineffective (although had the same effect as taking antibiotics), possibly due to lack of potency of the ‘active ingredient’ 55).
  • This 2009 double-blind randomized placebo-controlled multicenter trial 56) investigated the effectiveness of cranberry capsules (cranberry capsules contain 500 mg of the product, with 1.8% proanthocyanidins [9 mg]) to prevent urinary tract infection in older (aged 65 and older) long-term care facility (nursing home) residents. In participants with high urinary tract infection risk, twice-daily intake of cranberry capsules resulted in a 26% lower incidence of clinically defined urinary tract infection than placebo, but no difference was found in urinary tract infection incidence of strictly defined urinary tract infection 57). In residents with low UTI risk, twice-daily intake of cranberry capsules did not result in a lower incidence of UTI than with placebo.
  • In a 2016 year-long study 58) of 147 women living in nursing homes, taking two daily cranberry capsules decreased bacteria levels in their urine in the first 6 months of the study, but didn’t decrease their frequency of urinary tract infections over the year of the study, compared to taking a placebo. The two capsules together contained as much proanthocyanidin (72mg of the active ingredient proanthocyanidin), a compound that is believed to protect against bacteria, as 20 ounces of cranberry juice 59).
  • A 2012 research review 60) of 13 clinical trials suggested that cranberry may help reduce the risk of urinary tract infections in certain groups, including women with recurrent urinary tract infections, children, and people who use cranberry-containing products more than twice daily.
  • A 2012 research review of 24 clinical trials concluded that cranberry juice and supplements don’t prevent UTIs but many of the studies were poor quality 61).

Cranberry has not been shown effective as a treatment for documented urinary tract infection (UTI). Although cranberry may be used as an adjunct therapy in some cases, given the proven efficacy of antibiotics, cranberry should not be considered a first-line treatment 62).

Cranberry has been investigated for numerous other medicinal uses, and promising areas of investigation include prevention of H. pylori infection, which causes gastrointestinal ulcers and dental plaque 63).

Cranberry juice safety

Nausea, vomiting and diarrhea have occurred with large amounts of cranberry juice (3 cups daily) 64).

  • Drinking cranberry juice appears to be safe, although large amounts can cause stomach upset and may over time increase the risk of kidney stones 65). Cranberry contains high concentrations of oxalate, a component common to kidney stones.
  • Large doses of cranberry may alter levels of warfarin, an anticoagulant (blood-thinner).
  • People who think they have a urinary tract infection (UTI) should see a health care provider for a diagnosis and treatment. Don’t use cranberry products in place of proven treatments for urinary tract infections !

Summary

There have been a lot of studies in people of cranberry juice and cranberry supplement for urinary tract infections, but there’s very little high quality recent research on cranberry for other conditions. Among older women residing in nursing homes, administration of cranberry capsules (72mg of the active ingredient proanthocyanidin or equivalent to drinking 591 ml or 20 ounces of cranberry juice), compared with placebo, resulted in no significant difference in presence of bacteriuria (presence of bacteria in the urine) plus pyuria (presence of pus in the urine, typically from bacterial infection) over 1 year 66).

Cranberry juice does not appear to have a significant benefit in preventing urinary tract infections and may be unacceptable to consume in the long term. Cranberry products (such as tablets or capsules) were also ineffective (although had the same effect as taking antibiotics), possibly due to lack of potency of the ‘proanthocyanidin’ 67).

Raw cranberries, cranberry juice and cranberry extracts are a source of polyphenols – including proanthocyanidins, flavonols 68) and quercetin 69), 70). These compounds are being studied in human and in laboratory for possible effects on the cardiovascular system, immune system and cancer 71), 72), 73). However, there is no confirmation from human studies that consuming cranberry polyphenols provides anti-cancer, immune or cardiovascular benefits 74). Potential is limited by poor absorption and rapid excretion 75).

Drinking cranberry juice appears to be safe, although large amounts can cause stomach upset and may over time increase the risk of kidney stones 76). Cranberry contains high concentrations of oxalate, a component common to kidney stones.

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