Now, more than ever, it is especially important for us to find ways to help support our immune system. Below are some well known, and maybe not-so-well known strategies for boosting immune system function. What’s great is that these strategies all have actual research evidence supporting the claims and they can easily be implemented into your daily life!

1. SLEEP

There is extensive research supporting a connection between sleep and immune function. Sleep has been shown to enhance your body’s adaptive immune function and the development of immunological memory for fighting foreign invaders (see below, under “Vitamin D” for more information on adaptive and innate immunity).14

Acute and chronic sleep deprivation can negatively impact your body’s inflammatory homeostasis.14 These increases in systemic inflammatory markers due to habitual sleep deficits are linked to metabolic and cardiovascular disorders.15

During sleep, your body produces cytokines that support immune functioning and target infections. If you’re lacking in sleep, you’re going to be missing these important immune-boosting cytokines and thus, leaving yourself vulnerable to infections. Additionally, cortisol, epinephrine and norepinephrine are down-regulated during sleep. Conversely, drivers of cell growth and restoration, such as growth hormone and melatonin, are increased while you sleep.14

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Cortisol is a stress hormone and increases in the presence of a threat (think of the fight or flight response). Cortisol also plays a role in homeostatic functioning of the body, including blood sugar and blood pressure regulation and inflammatory and energy levels.

Cortisol is an essential hormone to our survival, but chronic, elevated levels of cortisol can lead to health problems, including hypertension, diabetes, heart disease, obesity, mood disorders, among others. Cortisol also acts to regulate sleep/wake cycles. Chronic stress can lead to sustained, elevated cortisol levels which can lead to sleep deprivation and reduced immune function, increased systemic inflammation and chronic disease. Additionally, poor sleep quality, quantity and inconsistency in sleep schedules can lead to elevated cortisol levels.

Growth Hormone (GH) is an important player in immune system function. Research demonstrates that GH stimulates development of the thymus gland, which is responsible for the production of important immune cells.16 Approximately 70% of growth hormone is secreted during sleep.17 Deficiencies in GH can lead to impaired growth, body composition and metabolism, along with impaired immune system functioning.18

Recommendations

UCSD Center for Pulmonary and Sleep Medicine Top Tips for Healthy Sleep Hygiene:

1. Don’t go to bed until you are sleepy.

2. Establishing a normal bedtime routine and sleep schedule (going to bed and waking up at the same time every day) will help your body relax and prepare for sleep.

3. Avoid napping during the day. If you must nap, try to limit it to under 1 hour and avoid napping later than 3 PM.

4. Avoid high-intensity exercise right before bed as it can increase cortisol levels, which disrupts sleep.

5. Late night caffeine and alcohol can lead to reduced sleep quality so avoiding caffeine and alcohol before bed will help ensure that you get a good night’s sleep.20

According to the National Sleep Foundation, adults (age 18-64 years) should shoot for an average of 7-9 hours of sleep each night.19 They recommend that teenagers get roughly 8-10 hours per night, and older adults (65+ years) should get between 7-8 hours of sleep per night.19

2. VITAMIN D

Outside of the more commonly known role of vitamin D as a mediator of bone health, vitamin D also plays a role in immune system functioning. Vitamin D activity has been found in many cells outside of those related to bone and mineral metabolism, including cells of the intestine, pancreas, prostate and immune system.9

Research has shown that deficiencies in vitamin D are associated with the onset of cardiovascular diseases, some cancers and autoimmune disorders, including type one diabetes, multiple sclerosis and inflammatory bowel disease.9 In a review of the literature on Vitamin D and its role in immune system functioning, Prietl et al concluded that vitamin D has important effects on cells in both the innate and adaptive immune system.10

Innate vs. Adaptive Immune Systems: The innate immune system consists of cellular, chemical and physical defenses. Innate immunity is present at birth and doesn’t require prior exposure to a pathogen to be activated. It is your first line of defense against outside invaders. It is non-specific and acts immediately upon appearance of a foreign body.

Adaptive immunity is your second line of defense against foreign substances. It is highly specific to the pathogen and is acquired from prior exposure. The adaptive immune system is slower to respond, but is able to recognize previous invaders thanks to memory T cells. The adaptive immune system is supposed to target non-self pathogens. However, autoimmune diseases arise when errors in the adaptive immune system occur, targeting the body’s own tissues.

Vitamin D has been shown to play a role in essential immune system functions and therefore, a deficiency in the vitamin may result in impaired immune responses and auto-immune disorder development.10

Recommendations: No consensus has been reached regarding recommended daily intake for vitamin D and establishment of a safe upper limit for supplementation. The Endocrine Society guidelines advise a safe upper limit for daily intake at 10,000 IU.11 The US Institute of Medicine, on the other hand, advises an upper limit of 4,000 IU/day.12 As much as 47% of daily vitamin D intake may come from supplementation.13 

Other sources of Vitamin D are sunlight (UVB) exposure and diet. For humans, vitamin D is mainly synthesized after exposure to sunlight (UVB) in the skin. Some vitamin D can also come from the diet such as from fish and certain mushrooms. More commonly, foods are fortified with vitamin D, as is seen with dairy products in the US.

3. VITAMIN C

Vitamin C supplementation has been shown to have positive effects on immune system function, through processes including antimicrobial activities, antioxidant properties, and inflammatory mediation.4,5 Additionally, vitamin C functions to assist in collagen production, contributing to the quality and maintenance of tissues throughout the body. Vitamin C is a powerful antioxidant and research has shown that it can effectively protect against some chronic and acute diseases.6

The US Institute of Medicine established a recommended daily intake of 75 mg for women and 90 mg for men.7  However, recent research may suggest that higher doses of vitamin C, up to 200mg/day, may provide additional benefits.8

Recommendations: Roughly 90% of our daily intake of vitamin C comes from fruits and vegetables.6 Citrus fruits and vegetables including broccoli, tomatoes and peppers are great vitamin C sources. It should be noted that vitamin C breaks down under heat and with storage, so eating fresh, raw fruits and vegetables will maximize the quality of your vitamin C intake. To get approximately 200mg of vitamin C, you will want to consume 5-9 servings of fresh fruits and vegetables each day.

4. GARLIC

In a review of the literature, Rodrigo Arreola et al. concluded that garlic may provide therapeutic effects related to immune system function through modification of action by macrophages, lymphocytes, natural killer cells and other immune system players.1 Their review revealed positive immunomodulatory and immunotherapeutic effects of garlic through direct stimulation of immune cells and other indirect pathways on metabolic syndrome, cardiovascular disorders, obesity, gastric disorders, and even cancer!

Recommendations: The effects of garlic can depend on the type, age, storage conditions, preparation and processing methods so be sure to change up how you prepare your garlic and the types utilized, to get maximum benefits!

5. EXERCISE

Exercise can have a negative or positive impact on immune function, depending on the frequency and intensity of the exercise! Prolonged periods of high-intensity exercise can reduce immune function, while regular, moderate-intensity training can enhance your immune system.2

For instance, in a study by Spence et al, researchers found that competitive athletes who underwent extended periods of high intensity exercise developed upper respiratory tract infections at a significantly higher incidence rate than recreational exercisers.3

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Regular, moderate exercise provides enhanced immune system function possibly due to its anti-inflammatory effects, alterations in immune cell composition, improved immunosurveillance, and positive effects of exercise on psychological stress management.2

Recommendations: Get in moderate exercise at least 3 times per week, for at least 30 minutes at a time. Incorporate both resistance training and cardio exercise into your regular routine.

This article was written by Kelly Wild, a licensed physical therapist and member of California Strength’s Olympic weightlifting team. You can connect with Kelly on Instagram @kellywild8 or book an in-person appointment with Kelly at Ironhorse PT & Pilates in San Ramon

Research:

1. Arreola, Rodrigo, et al. “Immunomodulation and Anti-Inflammatory Effects of Garlic Compounds.” Journal of Immunology Research, vol. 2015, 2015, pp. 1–13., doi:10.1155/2015/401630.

2. Simpson, Richard J., et al. “Exercise and the Regulation of Immune Functions.” Progress in Molecular Biology and Translational Science Molecular and Cellular Regulation of Adaptation to Exercise, 2015, pp. 355–380., doi:10.1016/bs.pmbts.2015.08.001.

3. Spence L, Brown WJ, Pyne DB, Pyne DB, Nissen MD, Sloots TP, McCormack JG, Locke AS, Fricker PA. Incidence, etiology, and symptomatology of upper respiratory illness in elite athletes. Med Sci Sports Exerc. 2007;39:577–586.

4. Wintergerst ES, Maggini S, Hornig DH. Immune-enhancing role of vitamin C and zinc and effect on clinical conditions. Ann Nutr Metab. 2006;50(2):85-94. doi:10.1159/000090495

5. Ang, Abel, et al. “Vitamin C and Immune Cell Function in Inflammation and Cancer.” Biochemical Society Transactions, vol. 46, no. 5, 2018, pp. 1147–1159., doi:10.1042/bst20180169.

6. Jens Lykkesfeldt, Alexander J. Michels, Balz Frei, Vitamin C, Advances in Nutrition, Volume 5, Issue 1, January 2014, Pages 16–18, https://doi.org/10.3945/an.113.005157

7. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: National Academy Press, 2000.

8. Frei, Balz, et al. “Authors' Perspective: What Is the Optimum Intake of Vitamin C in Humans?” Critical Reviews in Food Science and Nutrition, vol. 52, no. 9, 2012, pp. 815–829., doi:10.1080/10408398.2011.649149.

9. Holick, M.F. Vitamin D deficiency. N. Engl. J. Med. 2007, 357, 266–281.

10. Prietl, Barbara, et al. “Vitamin D and Immune Function.” Nutrients, vol. 5, no. 7, 2013, pp. 2502–2521., doi:10.3390/nu5072502.

11. Holick, M.F.; Binkley, N.C.; Bischoff-Ferrari, H.A.; Gordon, C.M.; Hanley, D.A.; Heaney, R.P.; Murad, H.M.; Weaver, C.M. Evaluation, treatment, and prevention of vitamin D deficiency: An Endocrine Society clinical practice guideline. JCEM 2011, 96, 1911–1930.

12. Institute of Medicine, Dietary Reference Intakes for Calcium and Vitamin D; Institute of Medicine: Washington, DC, USA, 2010.

13. Tripkovic, L.; Lambert, H.; Hart, K.; Smith, C.P.; Bucca, G.; Penson, S.; Chope, G.; Hyppönen, E.; Berry, J.; Vieth, R.; et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: A systematic review and meta-analysis. Am. J. Clin. Nutr. 2012, 95, 1357–1364.

14. Besedovsky, L., Lange, T. & Born, J. Sleep and immune function. Pflugers Arch - Eur J Physiol 463, 121–137 (2012). https://doi.org/10.1007/s00424-011-1044-0

15. Mullington JM, Simpson NS, Meier-Ewert HK, Haack M. Sleep loss and inflammation. Best Pract Res Clin Endocrinol Metab. 2010;24(5):775-784. doi:10.1016/j.beem.2010.08.014

16. Hirokawa K, Utsuyama M, Kikuchi Y. Trade off situation between thymus and growth hormone: age-related decline of growth hormone is a cause of thymic involution but favorable for elongation of lifespan. Biogerontology. 2016;17(1):55-59. doi:10.1007/s10522-015-9590-z

17. Van Cauter E, Plat L. Physiology of growth hormone secretion during sleep. J Pediatr. 1996;128(5 Pt 2):S32-S37. doi:10.1016/s0022-3476(96)70008-2

18. Ranke, M., Wit, J. Growth hormone — past, present and future. Nat Rev Endocrinol 14, 285–300 (2018). https://doi.org/10.1038/nrendo.2018.22

19. “How Much Sleep Do We Really Need?” Sleep Foundation, National Sleep Foundation, 1 June 2020, www.sleepfoundation.org/articles/how-much-sleep-do-we-really-need.

20. UCSD Center for Pulmonary and Sleep Medicine. Sleep Hygiene Patient Information Handout [Brochure]. San Diego, CA: University of California San Diego; 2017