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| 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 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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| Figure 1: Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart. Pop, population; RCT, randomized controlled trial (Somerville. 2016) |
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). |
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).
Figure 3: Effects of 1g of quercitin on URTI incidence in participants of 160km race in Western States (Hesnon. 2008) - 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).
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.
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.
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).
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! - 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.
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).
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).
- 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.
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| Don't forget: Cholesterol may also help you recover faster from infections! |
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.
Sick of Being Sick? 30 High Flavenoid Foods to Reduce the Incidence, Length & Severity of Infections by 40% (Avg.)
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