“Antioxidant” is a widely misunderstood word.
In most depictions, foodborne antioxidants get portrayed as good guys that free our bodies of villainous, DNA-damaging free radicals.
While antioxidants — which abound almost entirely in plant foods — are clearly beneficial, the reality in our bodies is more complex than the picture painted by marketers and the media (see Aging Theory Gets a Radical Makeover and Food-Borne Antioxidants Mostly Act Indirectly).
In brief, the antioxidants we get from foods benefit us mostly by exerting positive “nutrigenomic” effects on our genes, rather than by neutralizing lots of free radicals supposedly uncontrolled by the body’s own antioxidant network.
The richest and healthiest sources are whole, unprocessed plant foods, and there’s solid evidence that their non-vitamin antioxidants bring substantial health benefits: you'll find many relevant articles in the Food & Health/Antioxidants section of our newsletter archive.
In contrast, clinical studies haven’t found clear benefits from supplemental antioxidant vitamins: vitamin C, vitamin E, and beta-carotene (precursor to vitamin A).
And while fruit and vegetable juices do deliver some health benefits, they lack fiber, and fruit juices are very high in sugars, which surely blunts their benefits.
Non-vitamin food antioxidants come in two categories:
• Polyphenols include phenolic acids and flavonoids.
• Carotenoids include carotenes, lutein, zeaxanthin, and lycopene.
Now, a new analysis of data from a sizeable Danish population study sheds light on the preventive-health benefits of the flavonoid-type antioxidants found in many plant foods (see the "Flavonoids Family" chart, below).
Analysis of Danish study links antioxidants to reduced heart-cancer risks
The new study, led by scientists from Australia’s Edith Cowan University (ECU), involved Danish institutions and the International Agency for Research on Cancer.
As its authors noted, there’s a good deal of evidence linking higher intakes of flavonoid-class antioxidants to better health outcomes.
Due to the extreme difficulty and cost of testing the effects of different diets in controlled, "gold standard" clinical trials, virtually all evidence in this realm comes from epidemiological (population) studies.
Epidemiological studies cannot prove a cause-effect link between a food or nutrient and a health outcome. However, virtually all of the many relevant epidemiological studies link antioxidant-rich diets (i.e., ones relatively high in whole plant foods) to better health outcomes.
Still, as the authors of the new analysis wrote, “… evidence from observational [epidemiological] studies is incomplete ... [and] ... studies on cancer mortality are scarce.”
The authors of the new study analyzed data from the previously published Danish Diet, Cancer and Health Cohort (DCH) study — and they designed their analysis to remedy some of the deficiencies in the existing body of epidemiological evidence.
The DCH study involved 53,048 Danes, aged 50-64 years at the time of enrollment (1993-1997), who've now been followed for 23 to 27 years. All the participants provided detailed lifestyle information (e.g. diet, physical activity, and smoking), provided blood, fat-tissue, and nail samples, and permitted researchers to examine their health records.
The international team that conducted the new analysis estimated the amounts of different kinds of antioxidants in each DCH participant’s diet, then looked for links between intakes of specific antioxidants and the risk for developing heart disease and/or cancer.
The team first estimated the average amounts of flavonoids delivered daily by each participant’s diet, and then compared that data to the participants’ records in Denmark’s official health registry.
Perhaps unsurprisingly, given prior evidence of flavonoids’ benefits, the researchers concluded that diets high in flavonoid-rich foods like apple skins and tea help protect against cancer and heart disease — with smokers and heavy drinkers benefiting the most.
As the study’s lead researcher, Dr. Nicola Bondonno, said, “These findings are important as they highlight the potential to prevent cancer and heart disease by encouraging the consumption of flavonoid-rich foods, particularly in people at high risk of these chronic diseases.”
She added a cautionary note: “… flavonoid consumption does not counteract all of the increased risk of death caused by smoking and high alcohol consumption. By far the best thing to do for your health is to quit smoking and cut down on alcohol.”
Nonetheless, as Dr. Bondonno said, “We know these kind of lifestyle changes can be very challenging, so encouraging flavonoid consumption might be a novel way to alleviate the increased risk ...”.
How much antioxidant intake is enough?
The new analysis showed that people who averaged about 500mg of foodborne flavonoids daily enjoyed the lowest risks of dying early from cancer or heart disease.
Unfortunately, the average American adult consumes only 200 and 250 mg of flavonoids per day, with the main sources being tea, citrus fruit, citrus fruit juices, berries, red wine, apples, and legumes (beans and lentils).
Interestingly, official U.S. health surveys find that the “flavonoid density” of diets typically rises with age and income and is higher in women, Caucasians, and vitamin supplement users.
Dr. Bondonno noted that variety matters, because different flavonoid-type antioxidants bring different benefits: “It’s important to consume a variety of different flavonoid compounds found in different plant-based foods and drinks.”
And she illustrated how a person could get 500 mg of flavonoids daily: “This is easily achievable through the diet: one cup of tea, one apple, one orange, 100g (3.5 ounces) of blueberries, and 100g (3.5 ounces) of broccoli would provide over 500mg of a wide range of flavonoid compounds.”
These are some major types of flavonoids and a few examples of good food sources (also see the "Flavonoids Family" chart, below):
You'll find more complete, detailed lists of flavonoid-rich foods at Oregon State University’s Micronutrient Information Center.
Aside from flavonoids, there are many other beneficial polyphenol antioxidants in whole foods, such as the artery-loving tyrosols that abound in olives and extra-virgin olive oil, which averages 5.5 mg of polyphenols per tablespoon.
Dr. Bondonno acknowledged that the ways in which flavonoids protect from disease remain unclear, but as she said, “Flavonoids have been shown to be anti-inflammatory and improve blood vessel function, which may explain why they are associated with a lower risk of death from heart disease and cancer,” she said.
The anti-inflammatory effects of flavonoids would help explain why the study participants who reported drinking and smoking the most enjoyed the greatest flavonoid-linked reductions in heart and cancer risk:
As Dr. Bondonno noted, “Alcohol consumption and smoking both increase inflammation and damage blood vessels, which can increase the risk of a range of diseases.”
The takeaway from this analysis seems simple: eat a variety of colorful fruits and vegetables, and don’t expect their antioxidants and fibers to counter all the damage done by refined starches, sugars, and fried foods.
The Flavonoid Family
• Bondonno NP, Dalgaard F, Kyrø C, Murray K, Bondonno CP, Lewis JR, Croft KD, Gislason G, Scalbert A, Cassidy A, Tjønneland A, Overvad K, Hodgson JM. Flavonoid intake is associated with lower mortality in the Danish Diet Cancer and Health Cohort. Nat Commun. 2019 Aug 13;10(1):3651. doi: 10.1038/s41467-019-11622-x.
• Bondonno NP, Lewis JR, Blekkenhorst LC, Bondonno CP, Shin JH, Croft KD, Woodman RJ, Wong G, Lim WH, Gopinath B, Flood VM, Russell J, Mitchell P, Hodgson JM. Association of flavonoids and flavonoid-rich foods with all-cause mortality: The Blue Mountains Eye Study. Clin Nutr. 2019 Jan 17. pii: S0261-5614(19)30006-8. doi: 10.1016/j.clnu.2019.01.004. [Epub ahead of print]
• Chun OK, Chung SJ, Song WO. Estimated dietary flavonoid intake and major food sources of U.S. adults. J Nutr. 2007 May;137(5):1244-52.
• Frei B, Higdon JV. Antioxidant activity of tea polyphenols in vivo: evidence from animal studies. J Nutr. 2003;133(10):3275S-3284S. (PubMed)
• Ivey KL, Hodgson JM, Croft KD, Lewis JR, Prince RL. Flavonoid intake and all-cause mortality. Am J Clin Nutr. 2015 May;101(5):1012-20. doi: 10.3945/ajcn.113.073106. Epub 2015 Apr 1.
• Ivey KL, Jensen MK, Hodgson JM, Eliassen AH, Cassidy A, Rimm EB. Association of flavonoid-rich foods and flavonoids with risk of all-cause mortality. Br J Nutr. 2017 May;117(10):1470-1477. doi: 10.1017/S0007114517001325. Epub 2017 Jun 13.
• Kim K, Vance TM, Chun OK. Estimated intake and major food sources of flavonoids among US adults: changes between 1999-2002 and 2007-2010 in NHANES. Eur J Nutr. 2015; May 31. [Epub ahead of print].
• Lotito SB, Frei B. Consumption of flavonoid-rich foods and increased plasma antioxidant capacity in humans: cause, consequence, or epiphenomenon? Free Radic Biol Med. 2006;41(12):1727-1746.
• McCullough ML, Peterson JJ, Patel R, Jacques PF, Shah R, Dwyer JT.Flavonoid intake and cardiovascular disease mortality in a prospective cohort of US adults. Am J Clin Nutr. 2012 Feb;95(2):454-64. doi: 10.3945/ajcn.111.016634. Epub 2012 Jan 4.
• Oregon State University Micronutrient Information Center. Flavonoids. Accessed at https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/flavonoids
• Ponzo V, Goitre I, Fadda M, Gambino R, De Francesco A, Soldati L, Gentile L, Magistroni P, Cassader M, Bo S. Dietary flavonoid intake and cardiovascular risk: a population-based cohort study. J Transl Med. 2015 Jul 8;13:218. doi: 10.1186/s12967-015-0573-2.
• Sebastian RS, Wilkinson Enns C, Goldman JD, et al. A New Database Facilitates Characterization of Flavonoid Intake, Sources, and Positive Associations with Diet Quality among US Adults. J Nutr. 2015;145(6):1239-1248.
• Williams RJ, Spencer JP, Rice-Evans C. Flavonoids: antioxidants or signalling molecules? Free Radic Biol Med. 2004;36(7):838-849. (PubMed)