The evidence points towards flavonoids playing a role in preventing major chronic diseases such as cardiovascular disease and a number of cancers as well as asthma and possibly type 2 diabetes. Apples are a good source of flavonoids and often used in studies looking at the relationship between flavonoids and good health. Apples, as a popular food, are a major contributor of dietary flavonoids to an average Australian diet.
Western Australian research
Researchers at the University of Western Australia (UWA) have been studying the acute health effects of apples with particular focus on blood pressure, endothelial function, nitric oxide (NO) status, mood and cognitive function (Bondonno 2012 and Bondonno 2014). NO status is linked to vascular health and pathological conditions.
As a comparison apple with the skin left on was used as a high flavonoid food and apple with the flesh alone used as a low flavonoid food. High and low nitrate foods were also included in the study. At varying times volunteers consumed the high or low flavonoid foods alone and in combination with the high and low nitrate foods, after which various tests and measurements were taken.
The study found significant change in acute NO status but no improvement or deterioration in mood or cognitive function (Bondonno 2014). Apple with peel on and the high nitrate food independently lowered blood pressure, enhanced endothelial function and augment NO status. The study concluded that “Improvement of NO status, endothelial function, and blood pressure with dietary flavonoids and nitrate could play an important role in the prevention of cardiovascular disease” (Bondonno 2012). Flavonoids have a positive effect on endothelial function, blood pressure, atherosclerosis and reduction in risk of cardiovascular disease.
This research was part of a broader project looking at aspects of the selective apple breeding process and the market knowledge required to deliver a healthier flavonoid-rich apple to consumers.
Other studies
There have been numerous other studies around the world looking at the positive health effects of apples and flavonoids. A brief summary of some findings are given below. If you would like more information CSIRO conducted a review of Apple consumption and human health in 2010 and this information was summarised in the 2010 Apple report. Also refer to the short Apple Health Benefits summary produced by the US apple association.
In a Finnish study looking at a variety of chronic diseases they found that people that consumed higher levels of quercetin, one of the main flavonoids found in apples, tended to have a lower incidence of ischemic heart disease, lung cancer and asthma and also trended towards lower incidence of type 2 diabetes. The higher quercetin intake in diets was mainly attributable to the consumption of apples (Knekt et al 2002).
Another study looking specifically at cardiovascular disease also found that a diet consisting of flavonoid rich foods was associated with a reduced risk of death due to cardiovascular disease (Mink et al 2007). Apples and apple flavonoids are also thought to have a positive effect on cholesterol levels by lowering them (Nagasako-Akazome et al 2007; Jensen et al 2009).
Research looking into asthma and respiratory diseases have found that there is a link between apple consumption, and particularly the flavonoids in apples, and lower asthma and bronchial hyperactivity (Woods et al 2003), lower risk of developing asthma (Shaheen 2001) and also possible alleviation of sneezing attacks and reduced symptoms of persistent allergic rhinitis (Enomoto et al 2006). One study found that at the age of five children whose mothers ate apples while pregnant exhibited fewer symptoms of childhood asthma and allergic disease, suggesting they may provide some protective effect (Willers et al 2007).
The link between flavonoids and apple consumption and a number of cancers has been studied. In a long term population study comparing diet history and incidence of cancer they found an inverse association between flavonoid consumption and incidence of cancer, particularly lung cancer (Knekt 1997). Another study has also found and an inverse association between intake of quercetin and risk of lung cancer (Marchand 2000) and a similar inverse association has also been found for pancreatic cancer, particularly for current smokers (Nothlins 2007). Inverse correlation between apple consumption and colorectal cancer is thought to be due to the rich content of flavonoids and other polyphenols (Jedrychowski 2010).
In laboratory study flavonoids in apple peel were isolated and activity against human liver, breast and colon cancer cells evaluated. They found high potential anticancer activities against the three human cancer cell lines (He 2007).
References
Bondonno, CP, Xingbin Yang, Croft, KD, Considine, MJ Ward, NC, Rich, L, Puddey, IB, Swinny, E, Mubarakaeh, A and Hodgson, JM 2012, ‘Flavonoid-rich apples and nitrate-rich spinach augment nitric oxide status and improve endothelial function in healthy men and women: a randomized controlled trial’, Free Radical Biology & Medicine 52, 95–102
Bondonno, CP, Downey, LA, Croft, KD, Scholey, A, Stough, C, Xingbin Yang, Considine, MJ, Ward, NC, Puddey, IB, Swinny, E, Mubarak, A and Hodgson, JM 2014, ‘The acute effect of flavonoid-rich apples and nitrate-rich spinach on cognitive performance and mood in healthy men and women’, Food Function 5, 849
Enomoto, T, Nagasako-Akazome, Y, Kanda, T, Ikeda, M & Dake, Y 2006, ‘Clinical effects of apple polyphenols on persistent allergic rhinitis: A randomized double-blind placebo-controlled parallel arm study’, Journal of Investigational Allergology Clinical Immunology, 16, 283-289
He, Xiangjiu and Liu, Rui Hai 2007, ‘Triterpenoids isolated from apple peels have potent antiproliferative activity and may be partially responsible for apple's anticancer activity’, Journal of Agricultural and Food Chemistry, 55, 4366–4370
Jedrychowski, W, Maugeri, U, Popiela, T, Kulig, J, Sochacka-Tatara, E, Pac, A, Sowa, A and Musial, A 2010, ‘Case–control study on beneficial effect of regular consumption of apples on colorectal cancer risk in a population with relatively low intake of fruits and vegetables’, European Journal of Cancer Prevention, 19, 42-47
Jensen, EN, Buch-Andersen, T, Ravnharen, G and Dragsted, LO 2009, ‘Mini-review: The effects of apples on plasma cholesterol levels and cardiovascular risk - a review of the evidence’, Journal of Horticultural Science & Biotechnology, 34-41
Knekt, P, Järvinen, R, Seppänen, R, Heliövaara, M, Teppo, L, Pukkala, E and Aromaa, A 1997, ‘Dietary flavonoids and the risk of lung cancer and other malignant neoplasms’, American Journal of Epidemiology, 146, 223-230
Knekt, P, Kumpulainen, J, Jarvinen, R, Rissanen, H, Heliovaara, M, Reunanen, A, Hakulinen, T and Aromaa, A 2002 ‘Flavonoid intake and risk of chronic diseases’, The American Journal of Clinical Nutrition, 7, 560-568
Marchand, LL, Murphy, SP, Hankin, JH, Wilkens LR and Kolonel LN 2000, ‘Intake of flavonoids and lung cancer’, Journal of the National Cancer Institute, 92, 154-160.
Mink, PJ, Scrafford, CG, Barraj, LM, Harnack, L, Hong, CP, Nettleton, JA and Jacobs, DR 2007, ‘Flavonoid intake and cardiovascular disease mortality: a prospective study in postmenopausal women’, American Journal of Clinical Nutrition, 85, 895-909.
Nagasako-Akazome, Y, Kanda, T, Ohtake, Y, Shimasaki, H and Kobayashi, T 2007, ‘Apple polyphenols influence cholesterol metabolism in healthy subjects with relatively high body mass index’, Journal of Oleo Science, 56, 417-428
Shaheen, SO, Sterne, JAC, Thompson, RL, Songhurst, CE, Margetts, BM and Burney, PGJ 2001, ‘Dietary antioxidants and asthma in adults’, American Journal of Respiratory and Critical Care Medicine, 164, 1823-1828
Ute Nöthlings, U, Murphy, SP, Wilkens, LR, Henderson, BE and Kolonel, LN 2007, ‘Flavonols and pancreatic cancer risk: The multiethnic cohort study’, American Journal of Epidemiology, 166, 924-931
Willers, SM, Devereux, G, Craig, LC, McNeil, G, Wijga, AH, Abou El-Magd, W, Turner, SW, Helms, PJ and Seaton, A 2007, ‘Maternal food consumption during pregnancy and asthma, respiratory and atopic symptoms in 5-year-old children’, Thorax, 62, 773-779
Woods, RK, Walters, EH, Raven, JM, Wolfe, R, Ireland, PD, Thien, FCK and Abramson, MJ 2003, ‘Food and nutrient intakes and asthma risk in young adults’, American Journal of Clinical Nutrition, 78, 414-421