Since we are approaching the winter season, I decide to write a review of the foods that we can consume to reduce the risk of getting the colds and flu this winter. I usually develop common colds once a year, but sometimes I would have it longer than normal due to the stress of the work or lack of sleep from the daily activity. So this year I aim to reduce my chance of developing the colds and hopefully build a strong immune defense system to fight off the flu virus. I usually get a flu shot every year but fundamentally, I believe that building a strong immune system is the key step in keeping healthy and active this winter season.
Before we go any further, let’s understand what common colds really is. And what is the difference between common colds and flu?
Cold is an acute, self-limiting viral infection of the upper respiratory tract involving the nose, sinuses, and throat. The colds virus is usually spread by hand contact with secretions from an infected person (direct or indirect) or aerosol of the secretions and virus. The incubation period varies but is just under two days for rhinovirus. Rhinovirus accounts for about 50% of clinical cases.
The common symptoms of colds include a sore throat, rhinitis, rhinorrhea, cough, and malaise. Symptoms that related to the infected mucosa, typically peak at 1–3 days and last 7–10 days. But they can occasionally persist for three weeks depending on the strain of the virus and the status of your immune system.
Although self-limiting, the common cold is highly prevalent and may be debilitating. People with influenza are usually sicker than those with the common cold. In contrast to common colds, flu usually have high temperature (fever), chills, headaches, myalgia, and malaise. Influenza can be serious in older people and those who are immunocompromised such as people taking immunosuppression drugs or steroids or undergoes chemotherapy.
What kind of foods that can reduce the risk of developing common colds?
Probiotics are your best friends in keeping the body from viral invasion. Clinical studies showed that regular consumption of probiotics associated with reduced risk of developing colds. Cochrane systemic review of 14 clinical trials showed that probiotics are effective in protecting an individual from developing upper respiratory tract infection compared to placebo1.
The intake of probiotics is also associated with reducing the use of antibiotics. It’s worth noting, that antibiotics are not effective against common colds and should be avoided.
In the pediatric setting, the probiotic of Lactobacillus strains (Lactobacillus GG), have been shown to be effective in reducing the risk for nosocomial gastrointestinal and respiratory tract infections in children hospitals2. Not only the probiotics reduce the chance of catching the colds but they are also reduce the duration of the colds as per latest meta-analysis of 20 randomized controlled trials published in British Journal of Nutrition (2014)3.
These good friendly bacteria in your guts not only keep the bad bacteria at bay but also keep the immune system strong in fighting off the virulent viruses. The higher diversity of the good bacteria in your guts, the better as each stain of probiotics have their own secrets weapon in fighting off other bad bacteria. The best sources of probiotics include yogurts, kefir and fermented foods such as kimchi, tempeh, and miso soups.
Ginsengs have are famous for various health benefits in in Asian communities. One of them is for prevention and treatment of common colds and upper respiratory tracts infection. The most popular ginsengs are North American (Panax quinquefolius) and Asian ginseng (Panax ginseng) root extract.
Clinical studies showed that the number of colds in the group taking the ginsengs are significantly lower in that group that took the placebo. Not only that, when compared to placebo, ginseng significantly shortened the duration of colds by 6.2 days. The study found that North American ginseng appears to be effective in shortening the duration of colds or upper respiratory tract infection in healthy adults when taken preventatively for durations of 2-4 months4. Therefore, to gain the benefits of ginsengs, it should be taken at least 2 months before the cold/flu season starts.
Garlic is known to have antimicrobial and antiviral properties that are beneficial in preventing and treating colds and flu. Garlic contains numerous bioactive compounds that can enhance the function of the immune system such as Natural Killer cells and T-cells which are cells that go around the body and kill the invading viruses.
A study by the University of Florida showed that garlic supplementation reduces the number of symptoms (21% fewer compared to placebo). The group that takes garlic supplement also have a shorter duration of cold (61% less). The incident of cold is also halved in the group taking garlic supplementation5.
Similar finding also reported using aged garlic supplementation. The study showed that aged garlic supplementation reduce cold and flu severity, with a reduction in the number of symptoms, the number of days participants functioned suboptimally, and the number of work/school days missed6.
A clinical study using formulation of Camellia sinensis (green tea) capsules showed that tea stimulates proliferation gamma-delta T cells by 28% and associated with increased production of interferon (small protein produced by T-cells that kill viruses) compared to placebo. The group that took green tea supplement have fewer symptoms and a shorter duration of the cold. Therefore, tea is a safe and effective dietary strategy for preventing cold and flu symptoms. Maybe you can replace your morning and evening coffee with green tea during the cold season.
Cranberry juice is one of my favorite juice (especially when mixed vodka!). Luckily the benefits of cranberry juice not only limited to reducing the chance of getting urinary tract infections. A recent study showed that cranberry juice able to stimulate cells of the immune system to fight off cold and flu viruses. The study found that consumption of cranberry polyphenols able to reduce the symptoms due to cold and influenza7.
After reading this, you now have a secret dietary recipe for the winter to fight off the cold and flu this season. I hope this review will help you to achieve optimal health during this upcoming winter season.
- Hao, Q., Lu, Z., Dong, B. R., Huang, C. Q. & Wu, T. in Cochrane Database of Systematic Reviews (ed. Dong, B. R.) (John Wiley & Sons, Ltd, 2011).
- Hojsak, I. et al. Lactobacillus GG in the Prevention of Nosocomial Gastrointestinal and Respiratory Tract Infections. Pediatrics 125, e1171–e1177 (2010).
- King, S., Glanville, J., Sanders, M. E., Fitzgerald, A. & Varley, D. Effectiveness of probiotics on the duration of illness in healthy children and adults who develop common acute respiratory infectious conditions: a systematic review and meta-analysis. Br. J. Nutr. 112, 41–54 (2014).
- Seida, J. K., Durec, T. & Kuhle, S. North American (Panax quinquefolius) and Asian Ginseng (Panax ginseng) Preparations for Prevention of the Common Cold in Healthy Adults: A Systematic Review. Evidence-Based Complement. Altern. Med. 2011, 1–7 (2011).
- Nantz, M. 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. Clin. Nutr. 31, 337–344 (2012).
- Percival, S. S. Aged Garlic Extract Modifies Human Immunity. J. Nutr. 146, 433S–436S (2016).
- Nantz, M. 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. Nutr. J. 12, 161 (2013).