The common cold places a large burden on society in terms of suffering and economic loss due to its frequency of incidence. Worldwide, adults have on average about two to four common cold episodes a year, whereas children could experience between six and 10 colds a year. Most colds are initiated by one of more than 100 rhinoviruses, while flu symptoms are usually attributed to the influenza or parainfluenza viruses. However, many other respiratory viruses and bacteria can also cause cold and flu symptoms, such as the enteroviruses, coronaviruses, metapneumoviruses and respiratory synctial viruses.

All viruses cause the common symptoms of sneezing, blocked nose, irritation of mucous membranes, excess mucus production, sinusitis, cough, sore throat, fatigue, headache and fever. Flu symptoms tend to be more severe than those of a common cold and may involve the lower respiratory tract and lungs, potentially resulting in bronchitis or pneumonia. Colds and flu can also cause an exacerbation of asthma and chronic obstructive pulmonary disease (COPD).

There are various nutritional and herbal supplements that have been shown through clinical trials and other research studies to be beneficial in the prevention and treatment of the common cold and flu. Reviewing the evidence for the efficacy of vitamins, minerals and herbal supplements reveals a significant role they can play in fighting infection and keeping the bugs at bay.

Zinc

Zinc is necessary for the optimal functioning of your immune system. Inadequate zinc status can be triggered by many factors, such as exposure to disease agents, environmental features, stress, immunosuppression or ageing. When you are zinc deficient your immune responses become impaired and you are at an increased risk of infection. Zinc is necessary for normal development and function of cells that mediate your immune response.

Because zinc is not stored in the body, regular dietary intake of the mineral is important in maintaining the integrity of your immune system. Inadequate intake can lead to zinc deficiency and compromised immune responses. Zinc deficiency impairs various immune cell mechanisms that fight off invading pathogens. Zinc-deficient individuals are known to experience increased susceptibility to a variety of infectious agents. Zinc supplementation has been shown in numerous studies to reduce the risk of infection and reinfection.

Studies have shown that zinc inhibits the replication of the rhinovirus. In 2011, a review of 15 randomised controlled trials on zinc published in the Cochrane Database of Systematic Reviewsfound that zinc, in the form of lozenges or syrup, is beneficial in reducing the severity and duration of the common cold when taken within 24 hours of onset of symptoms. The study found that people supplementing with lozenges of 10–23mg of zinc every six hours during waking hours were less likely to have symptoms beyond seven days of treatment. It was also found that zinc supplementation in the form of syrup at 10–30mg a day for at least five months reduced the incidence of the common cold, school absenteeism and prescription of antibiotics in children.

In 2011, another review published in the Open Respiratory Medical Journal confirmed that taking zinc lozenges shortened the duration of colds. Three trials included in the review used zinc acetate in daily doses of greater than 75mg with the result indicating a 42 per cent reduction in the duration of colds. Five trials used a form of zinc other than zinc acetate in daily doses of greater than 75mg, the result indicating a 20 per cent reduction in the duration of colds.

The study also found that the local mechanism of action of zinc lozenges differed from the actions of systemic zinc on immune defences and that zinc’s role in immune support involved both a local and systemic mode of action. Short-term use of zinc lozenges has not resulted in serious side effects, though some study participants experienced gastrointestinal disturbances and mouth irritation.

Vitamin C

Vitamin C enhances your immune system through the significant role it plays in immune responses, including leukocyte and macrophage functions, neutrophil phagocytosis, antimicrobial activity, interferon synthesis and antihistamine properties.

In 1999, students aged 18 to 32 years reporting cold and flu symptoms were treated with 1000mg of vitamin C every six hours for three days, followed by 1000mg three times daily. This treatment resulted in an 85 per cent reduction of reported cold and flu symptoms compared with the control group. Another study found that either 4g a day or 8g a day of vitamin C administered on the first day of illness resulted in a reduction of cold duration. The average duration of cold episodes was 3.17 days in the 4g/day group, 2.86 days in the 8g/day group and 3.52 days in the placebo group.

A review published in the British Journal of Nutrition in 1997 analysed the results of six of the largest vitamin C supplementation studies and found that vitamin C intake was effective in reducing the incidence of the common cold in those who had a low dietary intake of vitamin C. High-dose vitamin C supplementation did not decrease common cold incidence in people who were not vitamin C deficient.

A meta-analysis of 30 placebo-controlled trials conducted in 2004 confirmed these results. It was found that supplementation with vitamin C at doses up to 2g a day did not decrease the incidence of common colds in people who were not deficient in vitamin C, although it did reduce the duration and severity of symptoms. However, for those exposed to continuous heavy exercise and/or stress due to low temperatures, such as marathon runners, skiers and soldiers on sub-Arctic exercises, doses ranging from 250mg to 1g a day of vitamin C reduced the incidence of colds by 50 per cent.

Vitamin C is available in many forms, but most experimental and clinical research uses ascorbic acid or sodium ascorbate.

Echinacea

Echinacea has been used traditionally for healing infections and wounds. Echinacea has antimicrobial and anti-inflammatory activity and it also plays a role in certain immune functions, such as the activation of phagocytosis. It is commonly used for respiratory tract infections such as the common cold, flu, sinusitis and tonsillitis. The German Commission E, the World Health Organization and the Canadian Natural Health Products Directorate have all advocated the use of echinacea for the common cold.

In 2007, a meta-analysis was conducted to evaluate echinacea for the prevention and treatment of the common cold, published in the journal Lancet Infectious Disease. Fourteen studies were included in the meta-analysis with results showing that echinacea decreased the incidence of common colds by 58 per cent and the duration of a cold by 1–4 days. This decrease in incidence and duration of the common cold was found to exist, despite the various factors that can influence the efficacy of echinacea, such as differences in concentration, species of echinacea, parts of the plant used and different doses.

In 2010, results of a review published in Phytomedicine found that echinacea had multiple actions in the treatment of colds and flu, including the inactivation of the viruses and certain pathogenic respiratory bacteria, including Streptococcus pyogenes (sore throat) and Hemophilus influenza pathogens. Echinacea purpurea was also shown to have anti-inflammatory activity by its ability to either completely or partly reverse the secretion of numerous pro-inflammatory cytokines. Echinacea purpurea also reversed the secretion of excess mucus, one of the most annoying symptoms of colds and flu. A combination of these activities is therefore beneficial in inhibiting viral and bacterial infection and in the amelioration of cold and flu symptoms.

In 2012, further research on the efficacy and safety of Echinacea purpurea extract in the prevention of the common cold was undertaken. The study was conducted over a four-month period, with 755 people receiving either an alcohol extract of Echinacea purpurea or a placebo. Participants recorded adverse events and rated cold-related issues in a diary throughout the study period. For episodes of acute colds, nasal secretions were sampled and screened for viruses. Results showed that echinacea reduced the total number of cold episodes, including pain-killer-medicated episodes. Analysis of nasal secretions confirmed that echinacea inhibited virally confirmed colds and particularly enveloped virus infections. It was also found that echinacea helped to prevent recurrent infections.

Selenium

Selenium is a mineral that has antioxidant properties, which help to protect cells from damage. Several studies have demonstrated that selenium deficiency results in decreased antibody responses. An antibody is a protein that is recruited by the immune system to identify and neutralise foreign objects such as viruses. Selenium deficiency also impairs functioning of macrophage, a type of white blood cell that ingests foreign material such as infectious micro-organisms. If you are deficient in selenium, you are at an increased risk of susceptibility to infections.

Selenium supplementation in individuals who are not overtly selenium deficient also appears to stimulate the immune response. In two small studies, both healthy and immunosuppressed individuals were supplemented with 200 micrograms a day of selenium as sodium selenite for eight weeks. Both groups showed an enhanced immune cell response to foreign antigens compared with those taking a placebo. The safe upper limit for selenium supplementation is 400mcg a day in adults.

Vitamin A

Vitamin A is essential for the growth and development of cells and tissues, and plays a particularly important role in the respiratory epithelium and the lung. It is also integral to the optimal functioning of the immune system due to its role in the normal functioning of several types of immune cells, including natural killer cells, macrophages and neutrophils.

Vitamin A deficiency is associated with an increased susceptibility to infectious diseases. During moderate vitamin A deficiency, the incidence of respiratory tract diseases is increased. Research published in both the Australasian Journal of Paediatrics and The Lancet has shown that repeated respiratory infections may be influenced therapeutically by a moderate vitamin A supplementation.

In 2012, a study involving 177 study participants was undertaken to assess whether vitamin A deficiency alters the recovery of airway function following acute upper respiratory tract infection. It was found that vitamin A contributes to preservation of airway function during and in recovery after upper respiratory tract infection in children.

Vitamin D

Vitamin D is a fat-soluble vitamin that shows promise for prevention of viral infections such as influenza and microbial infections. Your vitamin D levels are often lowest in the winter months when you have less exposure to the sun. In 2009, a systematic review of randomised controlled trials on vitamin D supplementation for the prevention or treatment of infectious disease found that vitamin D supplementation reduced the risk of acute respiratory illnesses and influenza.

In 2010, a randomised, double-blind placebo-controlled trial was undertaken to study vitamin D supplementation in preventing seasonal influenza A in schoolchildren. Influenza A occurred in 18 of 176 children in the vitamin D3 group compared with 31 of 167 children in the placebo group. Daily supplementation of 1200iu of vitamin D3 in schoolchildren between December and March showed a significant preventive effect against influenza A, although no significant difference was seen for influenza B.

A systematic review of clinical studies undertaken in 2012, published in the Journal of Steroid Biochemistry and Molecular Biology, analysed the use of vitamin D in the prevention of acute respiratory infection. The review included a total of 39 studies. Observational studies included in the review predominantly reported that a low vitamin D status was associated with an increased risk of upper and lower respiratory tract infections. The results from randomised controlled trials, however, were conflicting due to differences in dosages and vitamin D status in study participants.

Probiotics

Probiotics are live micro-organisms that help to improve the balance of beneficial bacteria in the digestive system. Your digestive system can contain 500 different species of micro-organisms. Ensuring you have lots of “good” bacteria in your gut can help to enhance both your digestive and immune health.

Several strains of probiotic micro-organisms have a positive influence on a wide range of immune functions. There has been a number of studies conducted showing the beneficial effects of probiotic supplementation on respiratory health. One of the earliest and significant studies conducted on probiotics and respiratory health in human populations was in 2000, where it was found that the supplementation of a bifidobacteria preparation in 129 children with acute respiratory tract infections enhanced the immune system through various immune mechanisms, including the stimulation of T-cell and B-cell immunity, natural killer cells and interferon release.

Another study conducted on Finnish children who consumed milk containing Lactobacillus rhamnosus GG during seven months over winter showed the children experienced 17 per cent fewer respiratory infections than the control group.

In 2005, a double-blind, placebo-controlled trial was published in the journal Clinical Nutrition. The study was undertaken to investigate whether the supplementation of probiotic bacteria Lactobacillus gasseri, Bifidobacterium longum and Bifidobacterium bifidum for at least three months in winter/spring affected the severity of symptoms, the severity and duration of common cold infections and the cellular immune response in otherwise healthy adults. A group of 479 adults were supplemented daily with vitamins and minerals. The control group did not receive the addition of the probiotic bacteria within their supplement. It was found that the use of probiotic bacteria significantly shortened the average duration of common cold episodes by about two days and also reduced the severity of symptoms. All immune cells investigated in the study were enhanced by the probiotic bacteria.

In 2011, a randomised, double-blind, placebo-controlled study using probiotic lactobacilli for strengthening the immune response against viral infections was published in the European Journal of Nutrition. Earlier positive research results on the use of probiotics for the common cold were confirmed, finding that Lactobacillus plantarum and Lactobacillus paracasei reduced the risk of common cold episodes, number of days with common cold symptoms, frequency and severity of symptoms and cellular immune response in common cold infections. The study involved 272 study participants who were supplemented daily with either 10 billion cfu of probiotics or placebo for a 12-week period.

Nutritional yeast supplements

Saccharomyces cerevisiae is a nutritional yeast supplement shown to have immune-enhancing properties. In 2010, research was published in the Journal of Alternative and Complementary Medicine demonstrating that supplementation resulted in a significant reduction in the incidence of colds and flu.

Beta-glucans are natural polysaccharides found in the cell walls of bacteria, yeast, fungi and algae but also in the walls of other plants and grains. Several studies have shown that a beta-glucan extracted from Saccharomyces cerevisiae strengthened the immune function in general, was able to improve resistance against various invading pathogens and was effective in reducing the incidence of cold and flu symptoms.

In 2012, the Journal of the American College of Nutrition published a study which found that daily dietary supplementation with a beta-glucan supplement extracted from Saccharomyces cerevisiae reduced upper respiratory symptoms.

Another double-blind, randomised, placebo-controlled study conducted on 100 individuals over a period of six months was published in the journal Food and Nutrition Sciences in the same year. Results demonstrated that beta-glucan extracted from Saccharomyces cerevisiae had a preventive effect on the occurrence of common colds compared to placebo. Those individuals taking beta-glucan had significantly fewer infections in the winter months. When common cold episodes occurred they were less pronounced and resolved more quickly.

Garlic

Garlic has long been used traditionally for treatment of common cold symptoms, while more recently laboratory evidence and scientific studies have confirmed its antibacterial and antiviral properties.

In June 2012, Clinical Nutrition published a study on the effect of aged garlic extract on the severity of cold and flu symptoms. A randomised, double-blind placebo-controlled trial involving 120 participants was carried out to determine the effect of aged garlic extract supplementation at a dose of about 2.5g a day on cold and flu symptoms. After 90 days of supplementation, the group consuming the aged garlic extract had reduced severity of symptoms, reduced duration of illness, reduced number of days where they functioned suboptimally and reduced number of school or work days missed due to illness.

In March 2012, the Cochrane Database for Systematic Reviews published results of a review on garlic for the common cold. Only one study fulfilled the criteria for the review in which 146 participants took garlic daily for three months. The study was randomised and placebo controlled. Participants in the garlic group had fewer colds than those in the placebo groups. The duration of the colds was roughly the same in all groups, between four and five days. The researchers concluded that daily consumption of garlic may help to prevent colds, but larger studies need to be done to confirm the possibility.

There are no randomised, controlled and properly conducted research studies to show if garlic reduces either the severity or length of a cold when a person begins to take it at the beginning of a cold.

Andrographis

Andrographis paniculata is a medicinal herb often used in the treatment of infectious respiratory diseases due to its role in stimulating the immune system. A systematic review of the literature on the use of andrographis for the treatment of upper respiratory tract conditions was undertaken in 2004 and published in the journal Planta Medica. Seven double-blind, controlled trials were included in the study, with results of the review demonstrating that andrographis is superior to placebo in alleviating the symptoms of upper respiratory tract infections. Evidence also suggested there may be a preventive effect. Adverse effects were mild and infrequent.

A randomised, double-blind, placebo-controlled trial published in Phytomedicine in 2010 found that treatment with a standardised extract of Andrographis paniculata reduced the symptoms of uncomplicated upper respiratory tract infection. In the trial, 223 patients received either 200mg per day of an andrographis extract (about 2.5g of herb containing 60mg of andrographolides) or a placebo for five days after experiencing symptoms of a common cold. Results were that both groups showed improvement in symptoms from days one to three. From days three to five, however, most of the symptoms in the placebo group were unchanged, while for the andrographis group symptoms continued to improve. The difference in the overall symptom score between the two groups was significant at day five. The overall efficacy of the andrographis group was approximately two times higher than placebo.

Elderberry (Sambucus nigra)

Elderberry has long been used in traditional medicine to treat influenza, colds and sinusitis. Elderberry contains high levels of flavonoids shown to have antiviral activity against respiratory synctial virus and parainfluenza and influenza viruses. Standardised elderberry extract has been shown to inhibit the replication of influenza A and B viruses in vitro and be effective in treating influenza B/Panama.

In 2004, the results of a randomised, placebo-controlled study on the efficacy and safety of elderberry syrup for treating Influenza A and B was published in the Journal of International Medical Research. The study involved 60 patients suffering from influenza-type symptoms for 48 hours or less. Patients received 15ml of elderberry extract or placebo four times a day for five days. Symptoms were relieved, on average, four days earlier and use of medication was significantly less in those receiving elderberry extract compared to the placebo group. Animal studies have also shown the efficacy of elderberry in the treatment and prevention of influenza-like symptoms in chimpanzees.

Olive leaf extract (Olea europaea)

The use of olive leaf extract has become popular for the treatment of colds and flu, with anecdotal reports indicating that olive leaf extract taken at the onset of cold or flu symptoms prevents or shortens the duration of illness. Research is also starting to emerge which confirms its antiviral and antibacterial effects.

Olive leaf extract, derived from the leaves of the olive tree, contains phenolic compounds such as oleuropein, which have demonstrated antimicrobial, antioxidant and anti-inflammatory activity in various laboratory studies. Oleuropein and elanolic acid have been shown to be effective in in-vitro and animal studies against many micro-organisms, including influenza and parainfluenza viruses as well as some bacteria.

Research suggests that the constituents of olive leaf interact with the protein of virus particles, thereby reducing infectivity and inhibiting replication of viruses known to cause colds, influenza and lower respiratory infection. In March 2013, a laboratory study revealed that olive leaf extract had antibacterial activity against both gram positive and negative micro-organisms. Olive leaf extract has also demonstrated an ability to stimulate phagocytosis, thereby enhancing your immune defence system.

At a glance
A to Zn: What the research reveals
 

Aged garlic extract at a dose of 2.5g a day for 90 days reduces the severity of symptoms and duration of cold and flu episodes.

Andrographis at a dose of 200mg a day (equivalent to 2.5g of herb containing 60mg of andrographolides) alleviates the symptoms of upper respiratory tract infections.

Echinacea decreases the incidence and duration of the common cold, inactivates viruses and certain respiratory bacteria and helps to prevent recurrent infections.

Elderberry flavonoids have antiviral activity against respiratory synctial virus, parainfluenza and influenza viruses. 15ml of elderberry extract four times a day for five days relieves symptoms on average four days earlier and reduces the need for medication.

Olive leaf extract has antiviral and antibacterial effects that may help to reduce the duration of colds and flu when taken at the onset of symptoms.

Selenium at a dose of 200mcg a day in the form of sodium selenite when taken for eight weeks enhances immune cell response to foreign antigens in both healthy and immunosuppressed individuals.

Vitamin A helps to prevent recurring respiratory infections and helps to preserve airway function and the recovery of airway function following a respiratory tract infection.

Vitamin C supplementation of more than 1g a day reduces the duration and severity of symptoms. Vitamin C supplementation offers prophylactic benefits for those exposed to continuous heavy exercise and/or stress due to low temperatures.

Vitamin D3 supplementation of 1200iu of vitamin D3 daily helps to prevent influenza A. Low vitamin D status is associated with an increased risk of upper and lower respiratory tract infections.

Zinc gluconate in the form of lozenges at a dose of 10–23mg at least three times daily or syrup at a dose of 10–30mg/day and taken within 24 hours after symptom onset reduces the duration and severity of common cold symptoms. Prophylactic zinc supplementation with a moderate continuous dose in those at risk of deficiency is beneficial to maintain respiratory health.

At a glance
Probiotics & nutritional yeasts

 

Probiotics

Bifidobacteria stimulates T-cell and B-cell immunity, natural killer cells and interferon release.

Lactobacillus casei reduces the duration of respiratory illnesses.

A combination of Lactobacillus gasseri, Bifidobacterium longumand Bifidobacterium bifidumof at least three months reduces the severity of symptoms and duration of common cold infections and enhances the cellular immune response.

Lactobacillus plantarumi andLactobacillus paracasei supplementation at a dose of 10 billion cfu for a three-month period reduces the risk of common cold episodes, number of days with common cold symptoms, frequency and severity of symptoms, and enhances the cellular immune response in common cold infections.

Yeasts

Saccharomyces cerevisiaesupplementation results in a significant reduction in the incidence of colds and flu.

Beta-glucan supplementextracted from Saccharomyces cerevisiae reduces upper respiratory symptoms, improves the resistance against various invading pathogens and helps to prevent the occurrence of common colds.

Immune cells and cellular immune responses

If natural supplements are not directly killing viruses or other infectious agents, their mechanism of action is to boost your immune response. Here is a quick guide to the various parts of your immune system that can be supported by these supplements:

Leukocyte

• White blood cell involved in defending the body against infectious disease.

Macrophage

• White blood cell that engulfs and destroys foreign particles such as bacteria.
• Stimulates lymphocytes and other immune cells to respond to pathogens.
• Slower than neutrophils to arrive to an area during an inflammatory response, but becomes increasingly involved in chronic infections.

Neutrophil

• White blood cell important in the acute stages of infection.
• Helps phagocytic cells kill and digest micro-organisms they have engulfed.
• The body’s main immune response to assaults by bacteria and fungi.
• Seem to have no effect on viruses and therefore are not useful in fighting viral infections such as the common cold.

Phagocytosis

• The cellular process of engulfing particles by the cell membrane to remove pathogens and cell debris such as dead tissue cells.

Interferons (IFNs)

• Proteins made and released by host cells in response to the presence of pathogens such as viruses, bacteria, parasites or tumour cells.
• Allow for communication between cells to trigger the protective defences of the immune system that help to eradicate pathogens or tumours.

Mast cells

• A type of white blood cell which, when stimulated, forms part of an early warning system that involves the release of chemicals such as histamine to signal either injury or infection and cause inflammation in the area.

Histamine

• Produced by basophils (a type of white blood cell) and mast cells as part of the immune response to foreign pathogens.
• Triggers the inflammatory response.
• Dilates blood vessels to attract cells to a site of damage.

 

Lifestyle tips to enhance immune health

Get adequate sleep

You’re more likely to catch a cold or other infection when you are sleep-deprived and fatigued. A small study showed that when sleep was limited to four hours a night for six nights, the immune systems of the study participants produced only half the normal number of antibodies when given a flu vaccine. Not getting enough sleep also increases the stress hormone cortisol, which results in increased inflammation in the body.

Practise relaxation or meditation techniques

Chronic stress suppresses the immune system, due to the effects of cortisol. Some studies have shown that people who meditate regularly may be able to increase their immune system response. In one study, people who meditated over an eight-week period produced more antibodies to a flu vaccine than people who didn’t meditate. Moreover, an increased immune system response was still evident four months later.

Take regular, moderate exercise

Studies show that regular, moderate exercise — for example, a daily 30-minute walk — increases the level of leukocytes, an immune system cell that fights infection. When you’re a non-exerciser, your risk of infections such as colds and flu increase compared to those who undertake moderate exercise.

Exercise is also associated with an increased release of endorphins, natural hormones that enhance mood and improve sleep quality, both of which have positive effects on the immune system.

Eat foods that enhance immunity

Malnutrition is the most common cause of immunodeficiency in the world. Nutrient deficiencies result in immunosuppression and dysregulation of immune responses, which increase your susceptibility to infection and illness. A diet rich in antioxidant vitamins and nutrients such as vitamin C, vitamin E, betacarotene and zinc can boost immunity to help fight infection. Increase your intake of these nutrients by eating an abundance of brightly coloured fruits and vegetables, including berries, citrus fruits, kiwifruit, apples, red grapes, kale, onions, spinach, sweet potatoes and carrots.

Other immune-boosting foods include fresh garlic, which has antiviral and antibacterial properties; mushroom varieties such as reishi, maitake and shiitake, which enhance immune function; and chicken soup. A study showed that if you do come down with a cold or the flu, a bowl of steaming chicken soup can boost immunity and help you recover faster.

Immune-boosting foods

Garlic

Garlic contains the active constituents allicin, ajoene and thiosulfinates, which all help to guard your body against cold and flu. To maximise the health benefits, you should crush the garlic at room temperature and allow it to sit for about 15 minutes. This will help to trigger an enzyme reaction that boosts the allicin content in garlic.

Mushrooms

Mushrooms are rich in nutrients and antioxidants, including the mineral selenium and B vitamins such as riboflavin and niacin. Studies have also shown mushrooms to have antiviral, antibacterial and anti-tumour effects.

Shiitake mushrooms are especially rich in beta-glucan, which activates your immune system and protects you against infections.

Oysters

Contain zinc in high amounts.

Watermelon

High in the antioxidant glutathione, which is found in the red pulpy flesh near the rind.

Grapefruit

High in vitamin C and flavonoids, which help to increase immune system activation.

Wheatgerm

If you are not wheat or gluten intolerant, wheatgerm is packed full of nutrients, such as zinc, antioxidants, vitamin E and the B vitamins, among other vitamins and minerals.

Sweet potatoes

High in vitamin A and beta-carotene.

Broccoli

Contains many nutrients that help to enhance your immune system, such as vitamin A, vitamin C and glutathione.

Ginger

Ginger is warming, promotes healthy sweating and reduces the inflammation of mucous membranes.

Carrot

High in vitamin C and a good source of beta-carotene, a precursor to vitamin A, which enhances your immune system, and helps to build your resistance against infections.

Berries

Brightly coloured berries such as blueberries, raspberries and cherries are all a great source of antioxidants, including anthocyanins, which prevent cells from damage and boost your immune system. Strawberries in particular are a great source of vitamin C.

Acai berry

High in anthocyanins.

Lemon

Lemons contain high amounts of vitamin C, which protects your body from cell damage and boosts your immune system. The rind of the lemon is also rich in limonene and liminoid substances that improve immune system functioning.

Chicken soup

Chicken contains cysteine, an amino acid that helps to reduce inflammation. Warm chicken broth prevents thickening of the mucus and relieves cough symptoms. Garlic and onion, which are often added to chicken soup, have immune-boosting effects, too.

Honey

Relieves sore throat and reduces coughing. Honey also contains a lot of antioxidants and has an antibacterial effect. Manuka honey is even higher in these antibacterial properties. A study conducted at Penn State College of Medicine showed that honey is an effective cough remedy. The study found that children given 1–2 teaspoons of honey before bed coughed less. Warm water with honey and lemon is a good remedy for relieving congestion and staying hydrated during bouts of colds and flu.

Foods that harm immunity

Sugar

Consuming too much sugar suppresses immune system cells responsible for attacking bacteria. This effect is seen for at least a few hours after consuming a sugary drink.

Fats

Diets that are high in saturated fats and trans fats depress the immune response and increase your risk of infection. Reducing these fats in the diet can enhance immune activity. It is important to include the “good” fats such as those derived from oily fish or seeds such as flaxseed in your diet to ensure you gain the beneficial effects of their anti-inflammatory properties.

Alcohol

Excessive alcohol intake impairs your immune system by reducing white blood cell count, making it difficult for you to fight off disease. Excess alcohol consumption also impairs the function of B-lymphocytes, which are responsible for the production of antibodies that ward off viruses and other diseases. In addition, excess alcohol consumption prevents nutrients being absorbed by the body.

Caffeine

In 2006, a study published in the Pharmacology, Biochemistry and Behavior found that men and women given large amounts of caffeine (three 250mg doses, equivalent to approximately 10 cups of coffee a day) experienced the release of high levels of the stress hormone cortisol in response to physical and mental stress. High levels of cortisol decreases the ability of your immune system to fight infections. However, it’s unlikely that a low to moderate intake of caffeine will detectably decrease the function of your immune system. According to the Mayo Clinic, a low to moderate intake of caffeine has few known health effects.

To ensure you get the best treatment possible in order to ward off nasty bugs and help prevent the onset of colds and flu this winter, talk to your health practitioner about the best nutritional and herbal medicines suited to you, and the possible side-effects and drug interactions of any supplements.

 

Saskia brown is a naturopath and health writer based in Sydney. E: saskia@saskiabrown.com W: www.saskiabrown.com