Sick of Being Sick? 30 High Flavonoid Foods to Reduce the Incidence, Length & Severity of Infections by 40% (Avg.)

If "that's you" and "that's you" more than four times a year, you better read today's SuppVersity article and learn which Flavenoids may reduce your number of upper respiratory tract infections into the normal range of 2-4 per year.
The number of purported anti-URTI (=anti Upper Respiratory Tract Infection) agents is unquestionable higher than the average number of yearly upper respiratory infections of the average US citizen, which is 2-4. Which of these usually natural agents actually have the ability to protect you from at least one of the previously cited 2-4 infections, however, is far from being obvious.

The scientific evidence is ambiguous and confusing and therefore I am happy that researchers from the University of Auckland and colleagues from the College of Sport and Exercise Science at the Victoria University have recently conducted a large-scale meta-analysis of no less than 387 studies - ok, that's the number they began with, obviously ;-)
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Since the aim of the meta-analysis was not to investigate all possible remedies, but only those that are based on naturally occurring flavenoids and their effects on the immune function in healthy adults, it should not surprise you that not all of those ~400 studies made it into the analysis. After the returned studies were initially screened, and 2 reviewers independently assessed the remaining studies for eligibility against prespecified criteria, only fourteen studies, of 387 initially identified, were included in this review.
Figure 1: Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart. Pop, population; RCT, randomized controlled trial (Somerville. 2016)
The primary outcome measure was the effect of flavonoids on URTI incidence, duration, and severity - outcomes of which not all were measured and every study. This and the differences in dosing, which ranged from 0.2 to 1.2 g/d reduce the significance of the authors' comparison, without making the meaningless, though.

With that being said, the scientists most general finding, i.e. that "[o]verall, flavonoid supplementation decreased URTI incidence by 33% (95% CI: 31%, 36%) compared with control, with no apparent adverse effects" (Somerville. 2016) may give hope to those of you who are way above the initially stated average of 2-4 infections per year.
Eat colorful! I know this advice doesn't sound exactly sexy, but it is - after all, flavenols are the molecules that give our foods (among other things) color... at least the natural foods, obviously not the artificially colored junk from the convenient area in the supermarket. The best way to get a full spectrum of "anti-infectious" flavenols would thus be to always combine differently colored fruits, vegetables, potatoes and grains (if you eat them) in your meals. A 2006 study by Thompson et al. even goes so far to suggest (and prove experimentally) that only a botanical diverse high fruit and vegetable intake will significantly affects reduce oxidative biomarkers in women.
Now, this wouldn't be the SuppVersity if I simply copy and pasted the tabular overviews from the meta-analysis. The latter are nice, but make it difficult for you to grasp which agents actually work and how well they reduced the incidence of URTI. Therefore I decided to take a different approach and to synthesize the most relevant data in a single figure (Figure 2).
Figure 2: Relative risk reduction due to supplementation of the given agents (see bulletpoints below for more legible information) and exemplary data from Niemann et al. (2007).
In that, I dropped all studies with "non-realworld" outcomes and stuck to those that actually measured the incidence of upper respiratory tract infections (URTIs) or rather the URTI risk reduction and supplement the data with some basic information on the individual studies, plus the results of the study with the most significant results (Niemann. 2007 | -91% risk!). Since I couldn't put all that info in the figure, here are the basics:
  • Figure 3: Effects of 1g of quercitin on URTI incidence in participants of 160km race in Western States (Hesnon. 2008)
    Henson et al. (2008) conducted a study in 9 healthy participants of the Western States Endurance Run (WSER / 160 km run); a double-blind parallel RCT, with 21-d supplementation of 1000 mg/day quercetin or placebo before the WSER and compared URTI occurrence vs. placebo (Figure 3); a comparison that yielded that had visible, but non-significant effects on the illness rate of the subjects (I would still consider this a success).
  • Nantz et al. (2012 & 2013) tested 2.56 g/d aged garlic extract (likewise a major source of quercitin) vs. placebo in 120 healthy subjects (60 per group) for 45 days in 2012 and a low calorie cranberry beverage (450 ml) made with a juice-derived, powdered cranberry fraction (n = 22) or a placebo beverage (n = 23) that was consumed for 10 weeks by 54 healthy subjects (17 men and 37 women), ranging in age from 21 to 50 years in 2013 and found that "aged garlic extract may enhance immune cell function and that this may be responsible, in part, for reduced severity of colds and flu" in Nantz et al. (2012 | -10% URTI risk).
    Table 1: Chemical characterization of the cranberry treatment and placebo beverages in the 2013 study by Nantz et al. that found a highly sign. 44% reduction in URTI symptoms / risk.
    A sign. more impressive reduction of -44% in URTI symptoms / risk, however, was observed one year later in Nantz et al. (2013) in their study with a cranberry beverage the composition of which you can find in Table 1.
  • You're missing the vitamins and aminos? Check out this older SV article and learn if vitamin C, D, E, glutamine, arginine & co promote or hamper immune health!
    Niemann, et al. (2007) investigate the effects of quercetin supplementation on incidence of upper respiratory tract infections (URTI) and exercise-induced changes in immune function in trained male cyclists (N = 40) who were randomized to quercetin (N = 20) or placebo (N = 20) groups and, under double-blind procedures. More specifically, the subjects received 3 wk quercetin (1000 mgIdj1) or placebo before, during, and for 2 wk after a 3-d period in which subjects cycled for 3 h/d at approximately 57% of their maximal wattage. You've seen the results of the study in Figure 2, already - quite impressive with quercetin protecting yielding URTI rates of 1/20 vs placebo = 9/20 (Kaplan–Meier analysis statistic = 8.31).
  • Riede et al. (2013) and Rowe et al. (2007) didn't use powders or drinks, but rather commercial immune boosters. Both, RestAid® and ImmuneGuard® worked, but contained very different ingredients.
    Table 2: Monthly illnesses and symptoms for subjects (healthy, 18-70 years) taking ImmuneGuard®, a combination of EGCG and theanine for three months (Rowe. 2007).
    While the former, i.e. RestAid® as it was used by Riede et al., contains an extract from the larch tree of which the scientists say that its arabinogalactan (a soluble fiber) and bioactive flavonoids are the active ingredients that produced a sign. reduction in common colds (p < 0.040) and the number of participants affected by the infection (p ¼ 0.033), the latter, i.e. ImmuneGuard® (see Table 2) which was used by Rowe et al. in 2007, contains a proprietary Camellia sinensis formulation (CSF) with EGCG standardized decaffeinated green tea and extra L-theanine (Suntheanine®), of which Rowe et al. were able to show that it had 32.1% fewer subjects come down with URTI symptoms (P < 0.035), reduced the number of overall illnesses (not just URTI) of at least 2 days duration by 22.9% (P < 0.092), and the number of days with symptoms by 35.6% (P < 0.002).
If we simply assume that you react similarly to the subjects in said studies, candidate supplements to get you through phases of increased infection risk are:
  • quercitin or high quercitin foods like citrus fruits, apples, onions, parsley, sage, tea, and red wine; olive oil, grapes, dark cherries, and dark berries such as blueberries, blackberries, and bilberries,
  • cranberry extracts or juices with and/or supplements or other foods containing proanthocyanidins and anthocyanins, like purple corn or sweet potatoes, black rice, aubergines, red cabbage, red onions, radishes or black beans, and - the obvious - red, blue and purple fruits (like cranberry, obviously),
  • larch extracts and/or dietary or supplemental arabinogalactan which can be found in very small quantities in a wide variety of foods including carrots, radishes, pears, corn, wheat and tomatoes, as well as
  • green tea and/or supplements containing EGCG and theanine, of which you already know that they have various benefits, such as increased fat oxidation with GTE or improved attention and reaction speed(s) with theanine.
So, eventually, the use of the the "right" flavenols (see list above) year-round may thus reduce the number of sick-days significantly. If we go by the numbers Somerville et al. calculated in their meta-analysis by as much as quite impressive 40%! - a reduction of which the meta-analysis suggests that it was not mediated by significant changes in bioimmune markers (e.g., interleukin-6, tumor necrosis factor-a, interferon-g, neutrophils), because those were "trivial between the intervention and control groups during the intervention and after exercise when a postintervention exercise bout was included" (Somerville. 2016).
Don't forget: Cholesterol may also help you recover faster from infections!
Bottom line: Even though the actual mechanism behind the anti-URTI effects of the previously listed flavenoids and the corresponding foods and herbs may not be clear, Somerville et al.'s findings "suggest that flavonoids are a viable supplement to decrease URTI incidence in an otherwise healthy population" (Somerville. 2016), or - in other words - they confirm that at least some of the often well-known remedies actually do what they are supposed to: reduce the risk, number and length of upper respiratory tract aka URTIs (and other infections), significantly.

What would be interesting, now, are head to head comparisons of the agents in the list I've compiled for you, as well as studies that investigate possible synergies and (even if those are unlikely) incompatibilities of  the agents in the list right above this conclusion | Comment!
  • Henson, D., et al. "Post-160-km race illness rates and decreases in granulocyte respiratory burst and salivary IgA output are not countered by quercetin ingestion." International journal of sports medicine 29.10 (2008): 856.
  • Nantz, Meri P., et al. "Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention." Clinical Nutrition 31.3 (2012): 337-344.
  • Nantz, Meri P., et al. "Consumption of cranberry polyphenols enhances human γδ-T cell proliferation and reduces the number of symptoms associated with colds and influenza: a randomized, placebo-controlled intervention study." Nutrition journal 12.1 (2013): 1.
  • Nieman, David C., et al. "Quercetin reduces illness but not immune perturbations after intensive exercise." Medicine and science in sports and exercise 39.9 (2007): 1561.
  • Riede, L., B. Grube, and J. Gruenwald. "Larch arabinogalactan effects on reducing incidence of upper respiratory infections." Current medical research and opinion 29.3 (2013): 251-258.
  • Rowe, Cheryl A., et al. "Specific formulation of Camellia sinensis prevents cold and flu symptoms and enhances γδ T cell function: a randomized, double-blind, placebo-controlled study." Journal of the American College of Nutrition 26.5 (2007): 445-452.
  • Somerville, Vaughan S., Andrea J. Braakhuis, and Will G. Hopkins. "Effect of Flavonoids on Upper Respiratory Tract Infections and Immune Function: A Systematic Review and Meta-Analysis." Advances in Nutrition: An International Review Journal 7.3 (2016): 488-497.
  • Thompson, Henry J., et al. "Dietary botanical diversity affects the reduction of oxidative biomarkers in women due to high vegetable and fruit intake." The Journal of nutrition 136.8 (2006): 2207-2212.
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