Malus species / Appel

De appel is verreweg de belangrijkste fruitsoort van het noordelijke halfrond. Ook wat het aantal rassen betreft staat de appel zeer hoog op de wereldranglijst. Hoe hoog is niet precies bekend. Conservatieve tellingen spreken van ongeveer 6000 rassen, waarvan overigens zeker de helft al lang in vergetelheid is geraakt; andere noemen getallen van 10000 of zelfs 20.000, al lijkt dat laatste cijfer wat aan de fantastische kant. Zeker is wel, dat het aantal rassen gestaag stijgt. Vooral de laatste jaren worden nieuwe rassen niet alleen gewonnen maar na beproeving ook regelmatig op grote oppervlakten aangeplant. Ze danken hun succes meestal aan eigenschappen als een hoge opbrengst, bewaarbaarheid en ook wel een zekere modegevoeligheid. Zo is in het recente verleden de populariteit van groene appels als de ‘Granny Smith’ plotseling toegenomen.Als cultuurvrucht is de appel al heel lang bekend, langer waarschijnlijk dan de peer. Dat valt onder andere af te leiden uit vondsten in Italië en Zwitserland, waar bij prehistorische paalwoningen resten zijn gevonden van gekweekte appels die al zo’n 4500 jaar geleden moeten zijn geteeld. Over de wilde voorouders van de moderne appel bestaat enige onzekerheid. Waarschijnlijk heeft de Europese wilde appel (Malus sylvestris) als stamsoort niet zo’n grote rol gespeeld. Dat is wel het geval met de Astrakanappel (M. prunifolia) uit Siberië en Noord-China en met Malus pumila uit de Kaukasus, waarvan in de Sovjet-Unie nog uitgestrekte wouden voorkomen.

Health benefits of apples: epidemiological evidence

Cancer

Several studies have specifically linked apple consumption with a reduced risk for cancer, especially lung cancer. In the Nurses' Health Study and the Health Professionals' Follow-up Study, involving over 77,000 women and 47, 000 men, fruit and vegetable intake was associated with a 21% reduced risk in lung cancer risk in women, but this association was not seen in men [18]. Very few of the individual fruits and vegetables examined had a significant effect on lung cancer risk in women, however apples were one of the individual fruits associated with a decreased risk in lung cancer. Women who consumed at least one serving per day of apples and pears had a reduced risk of lung cancer [18]. Of the men involved, there was no association seen between any individual fruit or vegetable and lung cancer risk.

In a case control study in Hawaii, it was found that apple and onion intake was associated with a reduced risk of lung cancer in both males and females [19]. Smoking history and food intake was assessed for 582 patients with lung cancer and 582 control subjects without lung cancer. There was a 40–50% decreased risk in lung cancer in participants with the highest intake of apples, onions, and white grapefruit when compared to those who consumed the lowest amount of these fruits. The decreased risk in lung cancer was seen in both men and women and in almost all ethnic groups. No associations were seen with red wine, black tea or green tea. Both onions and apples are high in flavonoids, especially quercetin and quercetin conjugates [20]. Le Marchand et al. [19] found an inverse association between lung cancer and quercetin intake although the trend was not statistically significant. Interestingly, the inverse association seen between apple and onion intake and lung cancer were stronger for squamous cell carcinomas than for adenocarcinomas.

In a Finnish study involving 10,000 men and women and a 24-year follow-up, a strong inverse association was seen between flavonoid intake and lung cancer development [15]. In the sampled population, the mean flavonoid intake was 4.0 mg per day, and 95% of the total flavonoid intake was quercetin. Apples and onions together provided 64% of all flavonoid intake. The reduced risk of lung cancer associated with increased flavonoid consumption was especially strong in younger people and in nonsmokers. Apples were the only specific foods that were inversely related to lung cancer risk. Since apples were the main source of flavonoids in the Finnish population, it was concluded that the flavonoids from apples were most likely responsible for the decreased risk in lung cancer.

The relationship of dietary catechins and epithelial cancer was examined in 728 men (aged 65–84) as part of the Zutphen Elderly Study [21]. Tea, a naturally high source of catechins, contributed 87% of the total catechin intake in this study, while apples contributed 8.0% of catechin consumption. It was found that total catechin and tea consumption did not have an effect on lung cancer, but apple consumption was associated with decreased epithelial lung cancer incidence [21]. This supported the findings of the previous studies discussed, where apples were significantly inversely associated with lung cancer, and may suggest that catechins alone do not play have a effect against lung cancers. Other data from the Zutphen Elderly study showed an inverse association between fruit and vegetable flavonoids and total cancer incidence and tumors of the alimentary and respiratory tract [22]. Again, tea flavonoids were not associated with a decrease in cancer risk.

Cardiovascular disease

A reduced risk of cardiovascular disease has been associated with apple consumption. The Women's Health Study surveyed nearly 40,000 women with a 6.9-year follow-up, and examined the association between flavonoids and cardiovascular disease [23]. Women ingesting the highest amounts of flavonoids had a 35% reduction in risk of cardiovascular events. Flavonoid intake was not associated with risk of stroke, myocardial infarction, or cardiovascular disease death. Quercetin did not have any association with cardiovascular disease, cardiovascular events, myocardial infarction or stroke. However, both apple intake and broccoli intake were associated with reductions in the risk of both cardiovascular disease and cardiovascular events. Women ingesting apples had a 13–22% decrease in cardiovascular disease risk.

In a Finnish study examining flavonoid intake and coronary mortality, it was found that total flavonoid intake was significantly inversely associated with coronary mortality in women, but not in men [24]. Apple and onion intake was also inversely associated with coronary mortality, especially in women. Data collected from this same cohort study also showed the effect of quercetin and apple intake on cerebrovascular disease [25]. Those who had the highest consumption of apples had a lower risk of thrombotic stroke compared to those who consumed the lowest amounts of apples [25]. Onion intake and quercetin intake were not associated with thrombotic stroke or other cerebrovascular diseases.

Apple and wine consumption was also inversely associated with death from coronary heart disease in postmenopausal women in a study of nearly 35,000 women in Iowa [26]. The intakes of catechin and epicatechin, both constituents of apples, were strongly inversely associated with coronary heart disease death. Although total catechin intake was inversely associated with coronary heart disease mortality, Arts et al (2001) found that tea catechins were not associated with coronary heart disease mortality in postmenopausal women. Apple catechins may be more bioavailable than the catechin and epicatechin gallates commonly found in teas.

The relationship between flavonoids and risk of coronary heart disease were also examined as part of the Zutphen Elderly Study [14]. Flavonoid intake was strongly correlated with a decreased mortality from heart disease in elderly men and also negatively correlated with myocardial infarction. Tea was the main source of flavonoids in this study and was also negatively correlated with coronary heart disease. Apple intake contributed to approximately 10% of the total ingested flavonoids and was also associated with a reduced risk of death from coronary heart disease in men, however the relationship was not statistically significant [14].

Asthma and pulmonary function

Apple consumption has been inversely linked with asthma and has also been positively associated with general pulmonary health. In a recent study involving 1600 adults in Australia, apple and pear intake was associated with a decreased risk of asthma and a decrease in bronchial hypersensitivity, but total fruit and vegetable intake was not associated with asthma risk or severity [8]. Specific antioxidants, such as vitamin E, vitamin C, retinol, and β-carotene, were not associated with asthma or bronchial hypersensitivity. Previously it had been found that apple intake, as well as selenium intake, was associated with less asthma in adults in the United Kingdom [27]. This study surveyed nearly 600 individuals with asthma and 900 individuals without asthma about their diet and lifestyle. Total fruit and vegetable intake was weakly associated with asthma, and apple intake showed a stronger inverse relationship with asthma. This latter effect was most clear in subjects who consumed at least two apples per week. Onion, tea, and red wine consumption were not related to asthma incidence, suggesting an especially beneficial effect of apple flavonoids. Vitamin C and vitamin E were not correlated with asthma incidence, and carotene intake was weakly, but positively, associated with asthma. Apple intake and orange intake were both associated with a reduced incidence of asthma in the Finnish study involving 10, 000 men and women [16]. Flavonoid intake in general was associated with a lower risk of asthma, and the association was attributed mainly to quercetin, hesperitin, and naringenin. Other fruits and vegetables, such as onions, grapefruit, white cabbage, and juices, were not associated with a decreased risk in asthma.

In a study of over 13,000 adults in the Netherlands, it was found that apples might beneficially affect lung function [28]. Apple and pear intake was positively associated with pulmonary function and negatively associated with chronic obstructive pulmonary disease. Catechin intake was also associated with pulmonary function and negatively associated with chronic obstructive pulmonary disease, but there was no association between tea, the main source of catechins, and chronic obstructive pulmonary disease [28]. A study of approximately 2500 middle aged (45–59 yrs) Welsh men also demonstrated a beneficial effect of apple consumption on lung function [29]. Lung function was measured as forced expiratory volume (FEV) in one second, and was positively correlated with citrus fruit, fruit juice/squash, and apple consumption. However, the association with citrus fruit and fruit juice/squash lost significance after adjustment for smoking. Apple consumption remained positively correlated with lung function after taking into account possible confounders such as smoking, body mass index, social class, and exercise. Participants who consumed five or more apples per week had a significantly greater FEV of 138 mL when compared to those who did not consume apples [29].

Diabetes and weight loss

Not only may apples help decrease the risk of heart disease, cancer, and asthma, but apple consumption may also be associated with a lower risk for diabetes. In the previously discussed Finnish study of 10,000 people, a reduced risk of Type II diabetes was associated with apple consumption [16]. Higher quercetin intake, a major component of apple peels, was also associated with a decreased risk in type II diabetes. Myrectin and berry intake were also associated with a decreased risk in type II diabetes, but onion, orange, grapefruit and white cabbage intake were not associated with a lowered risk.

Apple and pear intake has also been associated with weight loss in middle aged overweight women in Brazil [30]. Approximately 400 hypercholestemic, but nonsmoking, women were randomized to one of three supplement groups: oat cookies, apples or pears, and each subject consumed one of each supplement three times per day for twelve weeks. The participants who consumed either of the fruits had a significant weight loss after 12 weeks of 1.21 kg, whereas those consuming the oat cookies did not have a significant weight loss. Those consuming fruit also had a significantly lower blood glucose level when compared to those consuming the oat cookies [30].

Summary

Based on these epidemiological studies, it appears that apples may play a large role in reducing the risk of a wide variety of chronic disease and maintaining a healthy lifestyle in general. Of the papers reviewed, apples were most consistently associated with reduced risk of cancer, heart disease, asthma, and type II diabetes when compared to other fruits and vegetables and other sources of flavonoids. Apple consumption was also positively associated with increased lung function and increased weight loss. Partially because of such strong epidemiological evidence supporting the health benefits in apples, there is increasing research using animal and in vitro models that attempts to more clearly explain these health benefits.

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Over de geschiedenis van de appel: http://www.volkoomen.nl/M/malus.htm