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A Healthy Immune System to Optimise Cardiovascular Prognosis

Updated: Apr 29, 2020

12 APR 2020

Preamble: It’s to be underscored that a sustained, healthy immune function also confers a reduced risk of cancers and inflammatory disease.

Disclaimer. The content in this article is the work of the author(s), and is not associated with, and does not represent the opinions or policies of, CHI. It is provided for informational purposes only, and is not intended as, and should not be construed to be, legal, financial, medical, or consulting advice. References and links to third parties do not constitute an endorsement or warranty by the author(s).

As a physician and cardiologist, I am always mindful of my patients’ immunity status.

Why? Because clinically significant infections; especially respiratory infections, in susceptible patients increase the risk of acute coronary syndrome (ACS) – a term used to describe a range of conditions associated with sudden, reduced blood flow to the heart – which include heart attacks and heart failure.

A famed Veteran Affairs study from the US(1) found that in 600 hospitalized patients with confirmed diagnosis of influenza, 1 in 5 (24%) developed biochemical or clinical evidence of acute heart muscle damage/heart attack or myocardial infarction.

Now, a virtually identical observation has been documented in COVID-19 infection(2).

To maintain and optimise immunity against infections, especially viral infections:

What to do

Keep warm

Get enough sleep

Minimise major stressors

Light to moderate exercise

Hydration, good nutrition

Boost friendly microbiota

What to avoid

Excessive alcohol intake/binge drinking

Smoking - Nicotine inhalation

Heavily polluted/populated spaces

Breathing dry, stagnant or recirculated air

What to do

Keeping Warm

Fever during infection is a natural, evolutionarily preserved defence mechanism. It fires up a more effective immune response toward infections and creates a hostile environment for the invading bugs, mitigating their proliferation and survival.

In contrast, lower body temperatures (below 37oC) can diminish immune response, enhance virus replication and increase pathogen load on your body(3,4).

As we head into the cooler months, rug up, keep warm and stay hydrated. Use a humidifier if necessary. Exercise will also help, but make sure to keep your body warm and avoid inhaling cool dry air. Putting on a light scarf or a balaclava when working out outdoors can help with this, breathe through your nose – not your mouth.

What to do

Sleeping Patterns

Sleep deprivation is a big no-no when it comes to optimal health.

Numerous experimental and human studies including studies on shift workers consistently document the deleterious effect of poor sleep quality and lack of sleep hours on the immune function(5).

Identify and resolve the cause of your sleep problem where possible. Otherwise, the following recommendations may be useful:

  1. have regular exercise during the day – if you are physically tired, you are more likely to fall asleep at night. Avoid exercise within 2-3 hours of bedtime;

  2. limit caffeine intake – avoiding drinks and food containing caffeine after 1pm (coffee, energy drinks like Red Bull, tea, cocoa). Turn off electronic devices such as TVs, computers and laptops an hour before bed to limit systemic and visual stimuli;

  3. see a sleep psychologist (your GP may be able to refer you through the General Practice Allied Health Referral Scheme), or your GP themselves may be able to provide counselling;

  4. look into sleep aid supplements such as Melatonin, which is available in Australia via prescription or legal for Australian consumers to order online from reputable international companies (e.g. Metagenics NeuroCalm Sleep, 1-2 tablets 1 hour before bed or Life Extension Melatonin 3-10mg, 1 hour before bed).

  5. down-regulating brain activities and “dulling” your mind:

- read a book (nothing too exciting) or mediate (lots of apps out there to help you).

- have a small snack 30mins to an hour before bed (e.g. a small bowl of cereal with almond milk, warm milk with a piece of toast etc.).

- make your bed when you wake up and wash your sheets regularly so you can get into bed with tidy “fresh” sheets.

- make your bedroom as dark and quiet as possible.

What to do

Minimising Stress

Acute and chronic mental stresses are potent immune function depressants. Examples of chronic mental stresses include hostility, anxiety (GAD, or global anxiety disorder) and depression, and social isolation. Hostility is not anger – which is a short-lived emotion such as when you experience road rage – but rather the state of feeling antagonistic 24/7. A man who finds out his business partner had for years been systematically swindling him may regard her with hostility for the remainder of his life.

Acute stress such as sudden sickness in the family, bereavement, or marital breakup are also promoters of infective (viral) illness.

Practice these anti-stress measures(6):

  1. find a purpose for getting out of bed, remind yourself daily that you are mortal;

  2. find a hobby and form a habit around it; learn something new;

  3. join a group if you feel like it, choir groups, Probus, sporting clubs, church, men shed workshops are all good examples;

  4. socialise with friends and loved ones, even if only via video or over the phone;

  5. cultivate reading habits;

  6. engage in regular physical activity, (outdoor) exercise, gardening, walking your dogs, swimming and meditation are all great.

What to do


Regular exercise improves the immune system and reduces the risk of infection(7,8). As a minimum, walk 30 min per day, or 3-4 hours per week. A good gauge for exertion is to exercise until it’s uncomfortable to keep up a conversation or to hum a tune (talk test), or when you feel forced to use your mouth to breathe. It’s important to note that paradoxically, prolonged exercise to extreme exhaustion can actually acutely lower immunity, so try to avoid maximal efforts and being chronically tired as you’ll more likely suffer from (repeated) but generally minor infections, such as a cold.

What to do

Hydration and Nutrition

Infection and its associated fever promote dehydration. Maintain oral hydration – 1-2L of fluid per day – with water, weak tea, vegetable juice, Kombucha, and utilise hydrolytes if you’re sick; good hydration levels help to keep airways moist and mucus – one of our most important natural defences against infection – running. For additional hydration of the nasal passages, saline sprays are available at the chemist and in supermarkets; and for hydration of the skin, use unscented moisturisers.

We all know a “balanced” diet is essential to sustained good health. To help optimise our immune system, ample intake of the following may be useful(8-11):

  1. Dietary nucleotides are building blocks of our cells’ DNAs and RNAs. Meat (especially organ meat), seafood, legumes, seeds, and yeast are rich in nucleotides. Savoury yeast (eg. Nutritional Yeast Seasoning by Bragg) is one of the most wholesome protein and nucleotide sources (55% protein by weight), and is also rich in fiber (22% by weight) and B vitamins, whilst low in sodium and containing minimal fat. Savory yeast has a bland flavor and nicely blends with most food. You can sprinkle it on your toast, cereal, in pasta, soup, and on pizza, among other things.

  2. Omega3 from fish, seafood, seaweed and algae (vegan sources), flax, hemp and chia seeds, walnuts, edamame, kidney and soybeans.

  3. Flavonoids are antioxidants which give plants their colours. Certain flavonoids, especially those in flaxseed hulls (herbacetin), citrus (rhoifolin) and (Korean) thistles (pectolinarin) were shown to have potent inhibitory effects against corona virus a recent experimental study(12).

  4. Glutamine is an amino acid which is vital for preserving immune cell function and gut health against pathogens, its utilisation by our immune system escalating during infection. Meat, eggs, beans and fermented foods all contain high concentrations of Glutamine.

  5. Glutathione is a powerful antioxidant found in all living cells (spinach, avocados, asparagus and okra, cabbage, brussels sprouts, broccoli, garlic, chives, tomatoes, cucumber, almonds, and walnuts). Eating lots of sulphur rich foods (cruciferous vegetables like broccoli, brussels sprouts, cauliflower, kale, watercress and mustard greens; allium vegetables like garlic, shallots and onions; meat, fish) will promote production of glutathione in the body.

  6. Nitric oxide is a key molecule that participates in virtually every cellular and organ function in the human body. It can be found in beets, garlic, meat, dark chocolate, leafy greens, citrus fruits, pomegranate nuts and seeds.

  7. Short-chain fatty acids (SCFAs) – produced when fiber is fermented by friendly gut bacteria in the colon – are the main energy source for cells lining your colon and thus play an important role in colon health. Consumption of fiber-rich foods such as fruits, veg and legumes is linked to an increase in SCFAs.

  8. Sulforaphane (SFN), a sulphur containing molecule with potent anticancer properties found in brussels sprouts, broccoli sprouts, kale, broccoli, cabbage, bok choy, arugula, watercress, cauliflower, and collards. Eat raw or steam for 1-3 mins. Note that boiling, microwaving, or cooking vegetables on high heat, especially at temperatures greater than 140'C can severely reduce sulforaphane availability, by up to 10 times less.

  9. Vitamin C (vegetables and fruits), E (wheat germ, nuts – esp. almonds, pine and hazel nuts, fish –especially salmon and trout, abalone, sunflower seeds), A (cod liver oil, sweet potatoes, carrots, beans, black-eyed peas, spinach, broccoli, herring, tomatoes, apricots, melons, mango, sweet red pepper, spinach), and D.

  10. Zinc (meat, shellfish, legumes and seeds, nuts, dairy eggs and whole grains) and Selenium (beef, chicken, fish, organ meats, cottage cheese, brown rice and Brazil nuts).

Whilst a lot of these immune function modulators are also available as supplements, I’m largely in favour of utilizing dietary sources, namely, consumption through a variety of fresh whole foods. Wherever possible, eat foods raw or lightly cooked/steamed, avoiding cooking in batter, on BBQ and under high and prolonged heat wherever possible.

The role of microbiota(13). Trillions of microorganisms reside on our skin and in the lining of our orifices. They live in symbiosis with us, mostly as allies to fend off pathogens, help regulate our metabolism and enhance our health and immunity. So:

  1. Keep skin intact and take regular if not daily showers. Dry skin will crack and promote infection, so use moisturisers if/when necessary.

  2. Many of us experience swelling in the legs for a variety of reasons, which increase the risk of infections such as cellulitis. If you can’t avoid long periods of sitting, make sure to fidget and shake those legs, get up and walk around for a few mins for every hour you sit, elevate your legs (heels above groin if possible), use support stockings and seek medical treatment for the cause.

  3. Keep teeth and gums healthy with regular dental checks, as well as maintenance through brushing and flossing your teeth twice daily and using well fitted dentures. Bad breath can often be an early indicator of chronic infection or inflammation of your gums and teeth.

  4. Keep your nose moist through the use of saline nasal inhalers, humidifiers at home, and actively avoiding mouth breathing.

  5. Regular bowel habits indicate healthy guts. For optimisation, consume fibre-rich fruit and veg daily. Organic prunes, slippery elm, fermented vegan or dairy products (savory yeasts, low fat yogurts, low salt kimchi) may also improve gut health. Take pro or pre-biotic supplements if necessary but avoid chronic use of laxative medications.

What to avoid

Binge Drinking

Chronic and excessive alcohol intake and binge drinking adversely affects immune function, raising susceptibility to pneumonia, acute respiratory stress syndromes (ARDS) and delayed recovery from infection including poor wound healing(14). If you drink, stick to 1-2 standards per day.

What to avoid

Harmful Air

Smoking and inhaling polluted air can result in damage to the lining of our airways, increasing permeability and the risk of pathogens entering the lungs and blood stream where they can destroy your small airways (alveoli). This could mean that when you get a chest infection – risk of death from respiratory failure is heightened. Increased airway permeability has been shown to revert towards non-smoking levels with cessation so reduce or stop where possible. Refer to online resources to check levels of pollution in your area (e.g. OEH NSW Air Quality Index (AQI) - Hourly Report

On polluted days, choose your exercise time and place, or exercise indoors.

As we’ve discussed already, dry air causes cracks and inflicts damage to the lining of nasal passages and airways, so in dry weather consider using a humidifier at home, nasal saline sprays, engage in warm steamy showers, wear a scarf covering you nose when exercising and avoid mouth breathing.

If you are stuck in a congested space, breathe shallowly; if you are not well and find yourself in a space with recirculated air (where the air is largely also dry air, such as on public transport and in particular, airplanes) for an extended period of time, consider wearing a mask which will at least help keep your airways moist, and may reduce risk of infection, and make sure you’re well hydrated (refer to previous section on hydration).

What to avoid

Immunosuppressant Drugs

Certain drugs may reduce immunity. Immunosuppressants such as prednisone, hydrocortisone and cancer medications if prescribed constitute unavoidable components of your life which may contribute to reduced immunity. As with all drugs, their use should always be regularly appraised, balancing potential therapeutic benefits and adverse side effects.

Additional Tips

for Infection Prevention and Immune Function Optimisation

Intermittent fasting or periodic calorie restriction has been shown to stimulate regeneration of the immune system and thereby strengthen it. The bone marrow protects and optimizes immunological memory during dietary restriction(15,16).

Sleep position. If you have gastric reflux (GERD or gastroesophageal reflux disease), you may want to sleep with a raised bedhead (up to 20-45 degrees). Be aware that sleeping quite flat on your back (supine) can cause gastric juice to reflux into and cause injury to your airways, promoting respiratory infection. If you have obstructive sleep apnoea, sleeping on your back also is more likely to aggravate the effect of this medical condition(17). Conversely, sleeping prone, or on your stomach helps increase lung expansion and improve oxygenation(18). It’s not uncommon for patients in ICU with respiratory issues from lung infection to be encouraged to lie on their stomach in the prone position to improve blood oxygenation.

Alternate remedies are endorsed by other cultures such as Ling Zhi or Ganoderma Lucidum, types of mushrooms which have shown some evidence of reducing risk of in reducing risk of infection by modulating immune function(19-21). Traditional Chinese Medicine (TCM) has similar ample literature on multiple herbs which exert immune function modulation and seem to improve resistance to viral or bacterial infections(22).

Note that some of my recommendations in this article will not be suitable amidst social distancing during the period of COVID-19, whilst at the same time, it’s important to note the mental stress which accompanies social isolation adversely affects our immune function.

The author declares that there is no conflict of interest. The author has no financial or commercial interests or affiliations with products or companies mentioned in this article. This article is not sponsored.


  1. Acute cardiac injury events ≤30 days after laboratory-confirmed influenza virus infection among U.S. veterans, 2010–2012. Ludwig et al. BMC Cardiovascular Disorders 2015;15:109 DOI 10.1186/s12872-015-0095-0

  2. Cardiovascular Considerations for Patients, Health Care Workers, and Health Systems During the Coronavirus Disease 2019 (COVID-19) Pandemic. Driggin E et al. JACC Apr 2020. DOI:

  3. Temperature-dependent innate defence against the common cold virus limits viral replication at warm temperature in mouse airway cells. Foxman EF et al. PNAS 2015; 112 (3): 827-32.

  4. Fever: pathological or physiological, injurious or beneficial? Blatteis, CM et al. J Therm Biol 2003; 28, 1-13. doi:10.1016/S0306-4565(02)00034-7

  5. Sleep, stress, and immunity. Prather AA. Sleep and Health 2019, Pages 319-330.

  6. Stress and immunity in humans: A meta-analytic review. Herbert, T. B., & Cohen, S. (1993). Stress and immunity in humans: A meta-analytic review. Psychosomatic Medicine, 55(4), 364–379.

  7. Exercise, Immunity, and Illness. Arwel Wyn Jones and Glen Davison. Muscle and Exercise Physiology 2019, Chap 15, pages 317-344.

  8. Physical Activity and Diet Shape the Immune System during Ageing. Weyh C et al. Nutrients 2020, 12, 622; doi:10.3390/nu12030622.

  9. Role of glutathione in immunity and inflammation in the lung. Ghezzi P. Int J Gen Med. 2011; 4:105–113. doi:10.2147/IJGM.S15618

  10. The role of nucleotides in the immune and gastrointestinal systems: potential clinical applications. Hess JR and Greenberg NA. Nutr Clin Pract. 2012 Apr;27(2):281-94. doi: 10.1177/0884533611434933

  11. Dietary nucleotide improves markers of immune response to strenuous exercise under a cold environment. Riera J et al. (April 2013). Journal of the International Society of Sports Nutrition 2013;10 (1):20. doi:10.1186/1550-2783-10-20. PMC 3626726

  12. Nutrition, Immunity, and Infection. Calder PC and Kulkani AD. 1st edition 2017 Boca Raton. eBook ISBN9781315118901. DOI:

  13. Inhibition of SARS-CoV 3CL protease by flavonoids. Jo S et al. Journal of Enzyme Inhibition and Medicinal Chemistry 2020; 35(1):145–151.

  14. Role of the Microbiota in Immunity and Inflammation Belkaid Y et al. Cell 2014.

  15. Alcohol and the Immune System. Sarkar D et al. Alcohol Res. 2015; 37(2): 153–155.

  16. Collins N et al. Cell 2019.

  17. Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression. Cheng C-W et al. Cell 2014.

  18. Supine position related obstructive sleep apnea in adults: Pathogenesis and treatment. Joosten SA et al. Sleep Medicine Reviews 201418:7-17.

  19. Does prone positioning improve oxygenation and reduce mortality in patients with acute respiratory distress syndrome? Henderson WR et al. Can Respir J 2014;21(4):213-215.

  20. Randomized Clinical Trial for the Evaluation of Immune Modulation by Yogurt Enriched with β-Glucans from Lingzhi or Reishi Medicinal Mushroom, Ganoderma lucidum (Agaricomycetes), in Children from Medellin, Colombia. Int J Med Mushrooms. 2018;20(8):705-716. doi: 10.1615/IntJMedMushrooms.2018026986.

  21. White Button Mushroom Enhances Maturation of Bone Marrow-Derived Dendritic Cells and Their Antigen Presenting Function in Mice. Ren Z et al. J. Nutr 2008; 138: 544–550, 2008,

  22. Effects of the Medicinal Mushroom Agaricus blazei Murill on Immunity, Infection and Cancer. Hetland G et al. Scandinavian Journal of Immunology 68, 363–370. doi: 10.1111/j.1365-3083.2008.02156.x

  23. TCM Can Improve the Immune Reconstruction of HIV/AIDS Patients. TCM with antiretroviral therapy enhance immune response. Li X et al. 2020. Aids Research and Human Retroviruses. Doi: 10.1089/Aid.2019.0274

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