This post was written during the Covid-19 health crisis. Besides isolating at home, we have other tools to help protect ourselves by keeping our immune systems strong. This is especially important for older people, who have an age-related decline in immune strength (called immunosenescence).
With so little know about covid-19, there are no guarantees that these Immune Health Basics will provided added resistance for you, but a weakened immune system certainly won’t help.
I hope this post provides some comfort that there are things you can do to help protect yourself and the spread of the virus is not entirely out of your control. Be safe.
I will explain the research on: vitamins and minerals, food and supplements and lifestyle choices you can undertake to keep your immune system strong. To navigate this post, use this Table of Contents.
What is the Immune System?
The immune system is your body’s defence and repair system. The immune system is comprised of two parts – the innate and the acquired.
The Innate Immune System
This is the part of the immune system that we are born with and it includes our skin and mucus membranes which line our mouth, nose and GI tract. Our saliva, tears and even our sweat have built-in defences. All of these barriers help protect us from the outside world.
Our innate immune system also includes cellular soldiers such as neutrophils, macrophages, eosinophils, dendritic cells and the natural killer cells (such a great name). These are known as the white blood cells.
The Acquired Immune System
This system designs a specific attacker for each bacteria, virus or pathogen that invades our body. Cells of the acquired immune system include the T cells (made in the Thymus) and B cells (made in the Bone marrow).
Once you are exposed to a virus like the flu virus, rhino virus (cold virus) or Covid-19 corona virus, your acquired immune system creates an antigen against that specific invader. And you will have this antigen in your body for the rest of your life (although we don’t know for sure yet, how long covid-19 antibodies last).
You might ask “Why do I get the flu more than once then?” This is because there are different viruses that cause the flu. You will get a specific virus only once. The bad news is, you have to suffer through the effects of the flu to acquire this protection.
Since our immune system is so vitally important for keeping us healthy, you are probably wondering, what you can do to help keep it strong? Here is a summary of what I will cover.
Vitamin and Mineral Immune Health Basics
While you could argue that all essential vitamins and minerals are important for the immune system, there are nutrients that act directly on the cells of the immune system, and this blog post will focus on those, namely;
- Vitamin A
- Vitamin D
- Vitamin E
- Vitamin B6
- Vitamin B12
- Vitamin C
Food and Supplement Immune Health Basics
- Mushrooms, oats, barley and seaweed
- Omega-3 fatty acids
- Prebiotics and Probiotics
Lifestyle Immune Health Basics
- Stress management
- Physical activity
- Spending time in nature
Vitamin and Mineral Immune Health Basics
Vitamin A the name for a group of fat soluble vitamins. It’s most known for its role in good vision, but it also has other important jobs including supporting the immune system.
Vitamin A is important for healthy skin and mucus membranes as for that reason is an important for a healthy barrier defence. In addition to this, vitamin A is also important for the acquired immune system especially T and B cells. It seems to be particularly important for viruses and gastrointestinal infections (Elmadfa, 2019).
This chart shows you how much vitamin A you need.
If the nutrition facts panel of the label you are reading, gives the amount of vitamin A in IU (International Units) then used this conversion equations.
- 1 IU retinol = 0.3 mcg RAE
- 1 UI dietary beta-carotene = 0.3 mcg RAE
There are two main types of vitamin A and two main sources in our diet. Some vitamin A is already formed, and it is found in animal products like liver but also fish and diary.
The body can also make vitamin A from the pigments beta-carotene, alpha-carotene and beta-cryptoxanthin. These pigments are found in colourful fruits and vegetables like carrots, peppers and mangoes. Have a look at this list which shows where you can get both sources of vitamin A in the diet.
Everyone knows vitamin D as the sunshine vitamin. Because vitamin D is not found in many foods and because many people live either too far north or too far south of the equator to have a consistent supply of UVB from the sun, it is common for people to be vitamin D deficient.
For this reason, many health authorities, like the government of Canada recommends that all people over age 50 take a vitamin D supplement of 400 IU (10 mcg) per day (Health Canada, 2019).
In addition both Canada and the U.S. legislate that milk and margarine must be fortified with vitamin D. If you are choosing plant-based ‘milks’ in place of cow’s milk, then make sure you read the label to confirm that it also has vitamin D added.
Here are a list of food sources of vitamin D. Some are natural sources and the rest are fortified with vitamin D.
Vitamin E is the collective name for a group of related fat-soluble compounds and is well known as an anti-oxidant. It supports immune function but its effect is not linear. In a study with elderly subjects given vitamin E supplementation at 3 different doses; 60, 200 and 800 mg per day. It was the 200 mg dose that showed the best result (Meydani, 1997). This is equivalent to 134 mg of vitamin E in it’s natural form. It’s important not to take too much vitamin E.
Most importantly though, everyone should include food sources of vitamin E in your diet every day. You should aim for 15 mg per day, which is the Recommended Dietary Allowance (RDA) for adults. This chart from the National Institute of Health shows you your requirements.
Since vitamin E is a fat soluble vitamin, it is found if foods with fats and oils but is also found in small amounts in plant sources.
Vitamin B6 is one of the water soluble vitamins and is also important in supporting a healthy immune system. Water-soluble means that it is found in the water component of the food we eat and not the fat or oil portion. It also means that excess B6 will be excreted in urine and not stored in our fat cells.
B6 is actually seven different compounds, which have many roles in our body including metabolism and hemoglobin synthesis. If your vitamin B6 levels are too low, this can show itself as impaired glucose tolerance (higher than normal blood sugars).
A significant portion of elderly people have low vitamin B6 levels. The elderly also have a less robust immune system. Low B6 levels have also been seen in cancer patients and low B6 levels are associated with an increased risk of breast cancer. These links are being investigated to see if there is causation or just simply correlation.
In addition, it was observed in the Framingham heart study that participants with lower levels of vitamin B6 had higher levels of inflammation (Friso, 2001). This is important because inflammation is associated with cancer and other chronic diseases. Specifically, the Framingham heart study found that those with B6 depletion have lower levels of lymphocytes and higher levels of neutrophils. The fact that neutrophils are high indicates the presence of inflammation.
It is pretty easy to meet your requirement by eating a mixed diet as B6 is found in a variety of foods. Getting your B6 requirement from food is the preferred source—you will also get all of the other great nutrients that are found in the food.
Certain populations are more at risk for deficiency including the elderly, alcoholics and people with type 1 diabetes, liver disease and rheumatoid arthritis. If for some reason you are not able to meet your requirement via diet, then you could consider a supplement. The supplement could be in the form of a multivitamin, B complex or stand-alone vitamin B6. It is important to respect the dosage and remember that more is not better—the upper limit is 100 mg per day.
This Table from the Office of Dietary Supplements shows you the amount of vitamin B6 that you need at various stage of your life.
This table from the Office of Dietary Supplements shows you some selected dietary sources of vitamin B6.
Vitamin B12 is required for proper red blood cell formation. When it low, you can develop a type of anemia called magaloblastic anemia. Vitamin B12 is especially important for the immune response of natural killer cells and T cells (CD9+ T cells to be exact). This water soluble B vitamin is found only in animal products so it is particularly important for vegetarians to be conscientious about their food sources.
These are the recommended levels of vitamin B12.
Here are some food sources of vitamin B12.
This water soluble vitamin is another of the B vitamin family and is sometimes called vitamin B9 or folacin. Folate and B12 work together to optimize the immune system. Like vitamin B1, B2, B3 and iron, folate (called folic acid in it’s enrichment form) is added to white flour to improve the nutrition profile.
Food sources of folate are as follows:
Vitamin C, ascorbic acid is a water soluble vitamin and it protects immune cells from oxidative damage. When you are deficient in vitamin C, your immune cells can’t phagocytize (engulf and digest) invader cells (Elmadfa, 2019).
Scurvy is a well known disease of vitamin C deficiency and is very rare now. But low vitamin C blood levels and deficiency can still occur even if it doesn’t get to the level of scurvy. These low levels are more common in hospitalized patients, refugee camps and low income communities (Elmadfa, 2019).
In the last NHANES survey (2003-2004) vitamin C deficiency was founding 8.4 % of the U.S. population over age 20 and more common in men. In a Canadian study, 14% of women aged 20-29 who were all non-smokers were found to be deficient (Cahill, 2009). Smokers are another group that have higher rates of vitamin C deficiency.
It’s easy to get your daily requirement of vitamin C from your diet, especially if you like red peppers and citrus. You can see a selected list of foods with vitamin C here.
Iron is a mineral and largely found in hemoglobin in red blood cells which move oxygen from the lungs to the tissues. It is used in many parts of the body and is important for growth and neurological development among other important functions.
If you are deficient in iron, your immune system is compromised. For example, there is a higher prevalence of allergies in iron deficient children and adolescents and a higher risk of eczema and asthma when their mothers had low iron levels during pregnancy (Drury, 2016 and Bédard, 2018).
What is interesting about iron is that too little is detrimental to the immune system, but so is too much. Too much iron for example can inhibit the function of macrophages the ‘big eater’ immune cells that actually phagocytize invading cells. When a cell phagocytizes another cell, it surrounds and engulfs it.
This chart shows you how much iron a non-vegetarian needs. If you are vegetarian, your needs are 1.8 x higher. That’s because there are two types of iron in our food – heme and non-heme. Heme iron is in animal products and is more available to be absorbed by the body. The non-heme, plant sources, require more intake to achieve the same blood levels.
You can improve your body’s absorption of non-heme (plant) sources of iron by combining the food with vitamin C. For example, if you are eating some bean salad you can add a lemon or orange vinaigrette.
This chart shows you some common sources of iron in our food.
Selenium is a mineral and anti-oxidant and it is exactly that function that helps protect immune cells like phagocytes from oxidative damage. You maximize your immune function by reaching your requirement for selenium. Taking more selenium, than your body needs, does not help. You get maximum benefit by simply correcting a deficiency and not overloading (Elmadfa, 2019).
Selenium deficiency has been reported in areas of China but is rare in Canada and the U.S. (National Institute of Health, 2020). However, people on hemodialysis are more likely to be deficient as are people with HIV. It may also plan a role in cancer risk reduction.
Be careful not to overdo your intake, as selenium toxicity can happen with chronic high intakes, including symptoms of hair and nail loss, skin lesions, garlic odour in the breath and a metallic taste in the mouth and severe symptoms like kidney and heart failure.
You may see other charts with selenium contents of food that vary with this one. That’s because the selenium content of plant foods depending on the selenium content of the soil and this can vary widely. There is less variation in animal sources. An easy way to get your daily requirement for selenium is to eat 1-2 Brazil nuts per day. This chart shows you food sources of selenium.
Zinc is another mineral, found in a variety of foods, and used as an additive in throat lozenges. It’s important for wound healing as well as immune support. Even mild to moderate zinc deficiency can impair immune function. A low zinc level is associated with increased susceptibility to pneumonia.
When used in throat lozenges, several studies have described that the zinc with temporarily stick in the throat, which allows the zinc to make contact with the cold virus (rhinovirus). But they have to be taken within 24 hours of the first symptoms to be effective. It is not recommended as a nasal sprays or gels as several people have lost their sense of smell from these products (National Institute of Health, 2020)
You can see your requirements in this chart.
Zinc is in a wide variety of foods, but oysters are top of the list by far. It is also contained in denture adhesive cream (if you are using less that two 2.4 oz tubes per week, then you are within the safe limit for zinc consumption.
Zince deficiency in healthy North Americans is not common, but can occur in individuals after GI surgery or in those with ulcerative colitis, Crohn’s disease, or short bowel syndrome. People with chronic illnesses like diabetes, chronic liver disease, kidney disease, sickle cell, and cancer are also at risk for zinc deficiency.
Vegetarian can have lower amounts of zinc as the phytates in legumes bind the zinc. To help with this, vegetarians can soak beans, grains and seeds in water for several hours before cooking. Alternatively, these foods can be soaked until the sprout. Choosing leavened grains, like bread over unleavened like crackers and matzah, can help add more zinc to the diet.
Food sources of zinc are listed in the table:
It’s important to remember that taking a supplement is not an alternative to a healthy diet. The supplement should just be considered the safety net and not the long-term solution to a healthy diet. You need to respect the upper limits set by that National Institute of Health (U.S.) and Health Canada (the levels are the same for both countries).
If you need to take a supplement to correct a deficiency, you can stop taking it when your levels are normal but then make sure to include food sources of that nutrients so you can keep your levels within normal limits. In some cases, you may need long term supplementation, but for that consult with your health professional.
Choose a varied diet including whole foods that are good sources of Vitamins A, D, E, K, B6, B12, Folate and minerals iron, zinc and selenium.
Food and Supplement Immune Health Basics
Mushrooms, Oats, Barley and Seaweed
What do mushrooms, oats, barley and seaweed have in common? They all contain a type of fibre called beta-glucan. Each of these foods contains a slightly different molecule of beta-glucan and because of that, the effects are slightly different.
As people age, their thymus can not activate as many important immune cells called T-cells. This natural age-related decline in immune function is called immunosenescence. The beta-glucans found in mushrooms have shown to be particularly helpful in reversing this age-related decline in immune function (Nakashima, 2018). Because of this, mushrooms are said to have “immunostimulatory effects”.
The mushrooms shiitake, maitake and schizophyllum especially show ant-cancer protection. The beta-glucans in oats and barley have cholesterol-lowering effects and can lower post meal blood sugars and help prevent diabetes.
All mushrooms appear to have health benefits, even the common white mushroom. But because different mushrooms have different strengths – some are better at boosting the immune system, while others are stronger anti-inflammatories and still others are better at improving the type and quantity of good bacteria in our intestines, I would suggest you hedge your bets and include a variety of mushrooms in your diet and not just eat the same type all the time.
In addition, since the different beta-glucans have different effects, include oats, barley, seaweed and baker’s yeast in your diet as well.
Omega-3 Fatty Acids
There are two main types of omega-3 fatty acids. The type that comes from plant sources like flax seeds and walnuts called ALA and the types that come from fish and seafood called EPA and DHA.
One type of cell that is very important in our immune system are the macrophages (“big eaters”). They patrol the body looking for foreign cells and when they find them they destroy them by surrounding and engulfing them (called phagocytosis). Omega-3 fatty acids can increase the ability of the macrophages to phagocytize the immune cells.
In addition to the macrophages, the neutrophils are another important type of immune cell. They are the most abundant type of immune cell and they circulate in the blood, bone marrow, spleen and liver. They are the first cells on the scene when an invasion occurs and are important in clearing away the pathogen. Omega-3 has been shown (in animal study) that it can increase the phagocyte ability of neutrophils (Gutiérrez, 2019).
In addition, the omega-3’s are strong anti-inflammatories, which helps make sure that the immune response shuts off when it should.
The recommended intake of fish oil can be seen in this chart;
The foods that contain omega-3 are listed here:
In addition to being an anti-inflammatory, Omega-3 impacts T-cell mediated immune function. A high intake of fish oil can cause a reduction in T-cell mediated immune function, which is a bad thing.
This detrimental, adverse effect of a reduction in T-cell mediated immune function appears to be due to an increased antioxidant requirement with fish consumption. To test whether antioxidant supplements taken along with a fish oil supplement might prevent this adverse effect, researchers gave vitamin E at three different doses to 30 people age 65 and older.
The subjects received 100 international units (IU), 200 IU or 400 IU of vitamin E per day along with fish oil (Omega-500 TM, providing 1.5 g EPA, 1 g DHA and 5 IU vitamin E per day).
When fish oil was given with 100 IU and 200 IU of vitamin E per day, there was not an adverse effect of reduction in T-cell mediated function. In fact, there is an enhancement in T-cell mediated function!
The conclusion of the research study was that if you want to prevent the adverse effect of fish oil on T-cell mediated function, you needs to take fish oil along with 100 to 200 IU of vitamin E (Wu, 2006). The relationship between fish oil and vitamin E is called nutrient-nutrient interaction. Nutrient-nutrient interaction can explain why some research shows a benefit with fish oil supplements and others show a detriment.
In order to receive the full benefit of fish oil consumption, you should be sure to consume adequate vitamin E. The amount that research has shown to be effective is 100-200 IU per day. This amount can be pretty easily consumed in the diet (see the chart above).
This recipe for Salmon with grainy mustard and wheat germ topping is an example of how to combine omega-3 (salmon) with vitamin E (wheat germ).
Prebiotics and Probiotics
A probiotic is a live bacteria that provides us with a health benefit. These bacteria are found in fermented foods like, yogurt, kefir, kim chi and sauerkraut. According to the WHO definition, if the food is a true probiotic, then the bacteria will be live in the food in sufficient number, the bacteria will be able to survive the stomach acid and it will arrive in your intestines in sufficient quantity in order to offer a health benefit. Collectively, the probiotic bacteria that lives in our intestines is called our microbiota (also our gut microbiome, or our ‘good bacteria’ although in truth we have a mix of ‘good’ and ‘bad’)
A prebiotic is the healthy food that the bacteria eat. Yes, you have to feed them! In fact, there are more bacteria living in your body then there are human cells. But, don’t worry, these bacteria only eat what you can’t, namely fibre. Their favourite fibres are fructooligosaccharide (FOS), which is found in chicory root (called inulin), Jerusalem artichoke, garlic, onions and bananas, and galactooligosaccharide (GOS), which is made by enzymatic conversion of the lactose in cow’s milk.
As we age, our microbiota changes. Specifically, the number of putrefactive bacteria (especially Clostridium perfringens) increase, and the number of beneficial bacteria groups, (such as Eubacterium spp. and bifidobarteria), decline. The aging process also leads to a marked decline in immune function (immunosenescence). The change in bacteria in the gut is thought to be one of the reasons for immunosenescence.
This decline in immune function can manifest as reduced response to vaccines and reduced number of immune cells. There have been some study on prebiotic supplements and immune function in the elderly. Forty-four, free-living elderly people (28 women and 16 men) with an average age of 69.3 years were enrolled in the study. The study subjects were given a supplement (a galactooligosaccharide mixture called Bi2muno®), which they consumed for 10 weeks.
Galactooligosaccharide (GOS) is a prebiotic. This means that while it is indigestible by humans, it is a very nutritious food source for our gut bacteria. GOS is produced by enzymatic conversion from cow’s milk. The Bi2muno® supplement had a significant effect on all bacterial groups measured. The supplement reduced number of less beneficial bacteria and increased numbers of beneficial bacteria (Vulevic, 2008).
In addition to the beneficial changes in gut bacteria, the natural killer cell activity was significantly improved, as well phagocytosis, after the subjects took the prebiotic supplement. A more beneficial inflammatory response was also seen—anti-inflammatory cytokines were increased and the pro-inflammatory ones were decreased. These are all beneficial responses of the immune system to the prebiotic supplement.
Supporting the microbiota is a good strategy for supporting the immune system. It’s important to keep in mind that as we age, there is a corresponding decline in the probiotic bacterial population, as well as our overall immune function. So, this information is especially important for seniors.
In the human study, Bi2muno® provided good results. Bi2muno® is a commercially available prebiotic supplement. Galactooligosaccharides (found in the Bi2muno® supplement) appear only to be found as a supplement or in fortified foods (mostly from Japan). While there is a risk of taking live bacteria (probiotic) with a compromised immune system, this same risk does not exist for what is essentially a fibre supplement. But, like always, consult your health care professional before taking supplements.
Being a dietitian, I always like to mention dietary sources as well. Fructooligosaccharide is another form of prebiotic and it is found in several foods including:
- Chicory root (called inulin) and found fortified in some foods
- Jerusalem Artichoke
- Dandelion greens
- Wheat bran
- Whole wheat flour
Soy is a pretty controversial food. A healthy, plant-based protein but plagued by a bad reputation from early animal and cell culture studies of breast cancer. A reputation, that after years of study to the contrary still sticks.
Genistein, one of the isoflavones (plant estrogens) in soy, has been shown to have a positive impact on the immune system. It can enhance both cytotoxic T cells and natural killer cells. This can explain why the early studies that used only human breast cancer cells (in cell culture) or in nude mice (mice without an immune system) showed that soy increased the cancer cell growth. Since neither the nude mouse nor the cells have functioning immune system, the benefit wasn’t seen. But, as research continued on the relationship between soy and breast cancer, what emerged was the positive benefits from soy (genistein) on our immune system.
This chart also shows that traditional soy foods like 1 cup of tofu has 53 mg of total isoflavones, whereas 3 links of soy sausage have only 3 mg. The isoflavone content of soy protein concentrates vary from 12-102 mg depending on their preparation method. Because of the varying levels of isoflavones in foods, researchers will tend to report the isoflavone intake and not the soy food intake. Presenting the isoflavone content helps to make the results more valid.
If something bad happens to you, that is a stressor. You reaction to that situation is stress. This is important to clarify, ie. it’s not the situation that is stress, it’s your reaction to it. To some extend, you have control over how you react to things.
In a review that examined research on job stress and immune function, authors from the Occupational Health and Safety, Center for Disease Control concluded that job stressors are associated with a disrupted immune function and fewer natural killer cells (Nakata, 2012).
Researchers from Brazil suggest that older people may be more susceptible to stress related illness and a poor immune response to stress. On the flip side stress management and psychosocial support will promote a better quality of life for our older citizens (Bauer, 2009).
How do you manage stress? It takes practice and you need to implement a regular stress management routine into your day and/or week. Fifth could be as simple as taking the dog for a walk and it can be more formal like a mindfulness meditation class, or of course a combination of a lot of different strategies.
In a 2014 study of adolescents age 12.5-17.5 years, those who reported 8-9 hours of sleep had higher cytokines and lower inflammation (Pérez de Heredia, 2014).
In terms of how to get the best sleep, the best advice is to practice good sleep hygiene, which includes:
Physical activity and Exercise
Exercise and immune function is not such a straight forward relationship. It’s more of a “U” shaped curve. This means that a sedentary person has a lower immune response, a person who partakes in regular moderate exercise has a good immune system but following excessive or especially intense exercise, the immune system is weakened.
There are also dips and recovering of immune function the day of and the day following. Exercise initially causes a reduction in the immune system due to the stress to the body, similar to the immune depression with psychological stress. The body creates new T and B cells within to return to normal levels within 24 hours of the exercise (Walsh, 2016). Bottom Line; regular physical activity is your best bet for a strong immune system.
According to researchers in Japan, forest bathing or “Shinrinyoku” is a short, leisurely visit to a forest. It’s a type of natural aromatherapy. These studies on being in nature have shown to increase a person’s level of natural killer cells and other measures of immune function which lasted for more than 7 days after the trip (Li, 2010). The mechanism for the increase in natural killer cells is thought to be due to phytoncides (alpha-pinene and beta-pinene) natural tree aromatherapy.
There were some interesting results in a study of 33 women from the midwest were asked to watch a humorous video or a travel video then their natural killer cell level was measured. There was no difference in the two groups by comparing which video they watched, but when the researchers considered how much they laughed while watching the video, they saw a significant improvement in natural killer cells (Bennett, 2003).
Practicing regular stress management, getting enough sleep, regular moderate physical activity, spending time in nature and laughing are all lifestyle opportunities to support a healthy immune system. Take steps in prioritize these tasks which are often given low priority in our busy lives.
Immune Health Basics PDF Download
I created a summary of Immune Health Basics for you. Use these tools along with social distances, hand washing and recommendations from public health officials to stay healthy. Immune Health Basics PDF
Can My Immune System Protect me from Cancer?
Your immune system doesn’t just protect you against the flu and colds. There are parts of the immune system that also protect you from cancer. Unlike invading bacteria and viruses though, cancer cells (with some exceptions like H. pylori bacteria and human papilloma virus (HPV)) are your own body’s cells, but with a defect. This can make recognition by our immune system more challenging.
Have you ever heard that we all have cancer cells in our body but only some of us develop cancer? This is thought to be because the immune system keeps rogue cancer cells under control so that their numbers never get large enough to actually form a mass. However, when our immune system is overwhelmed, cancer cells can grow more rapidly and form into tumors. If this goes unchecked, the cancer can spread to other parts of the body.
If you would like to have a food guide that is focused on food and lifestyle choices to reduce cancer risk – including supporting your immune system, then check out my Cancer Risk Reduction Guide. Also, stay up to date with the latest on cancer nutrition by joining my email list.
References for Immune Health Basics
National Cancer Institute. Cancer Prevention Through Immunomodulation: Does Diet Play a Role? Sept 16, 2014.
Health Canada. Vitamin D and Calcium: Updated Dietary Reference Intakes. Date modified 2019-07-10. Date accessed Mar 20, 2019.
Meydani SN, Meydani M, Blumberg JB et al. Vitamin E supplementation and in vivo immune response in healthy elderly subjects. A randomized controlled trial. JAMA 1997. 277:1380-6.
Friso S, Jacques P, WilsonP et al. Low circulating vitamin B6 associated with elevation of the inflammation market C-reactive protein independently of plasma homocysteine levels. Circulation. 2001. 103:2788-2791.
Cahill L, Corey P, El-Sohemy A. Vitamin C deficiency in a population of young Canadian adults. Am. J. Epidemiol. 2009. 170 (4), 464-471.
Drury K, Schaeffer M, Silverberg J. Association between atomic disease and anemia in US children. JAMA Pediar. 2016. 170(1), 29-34.
Bédard A, Lewis S, Burgess S et al. Maternal iron status during pregnancy and respiratory and atopic outcomes in the offspring: A mendelian randomization trial. BMJ Open Respir. Res. 2018. 5(1) e000275.
Nakashima A, Yamada K, Iwata O et al. B-Glucan in foods and it’s physiological functions. J Nutr Sci Vitaminol. 64, 8-17, 2018.
Gutiérrez S, Svahn S and Johansson M. Effects of Omega-3 Fatty Acids on Immune Cells. International Journal of Molecular Sciences. 2019 20, 5028.
Wu D, Han S, Meydani M et al. Effect of concomitant consumption of fish oil and vitamin E on T cell mediated function in the elderly: a randomized double-blind trial. J Am Coll Nutr. 2006. Aug 25 (4):300-6.
Vulevic J, Drakoularakou A, Yaqoob P et al. Modulation of the fecal microflora profile and immune function by a novel trans-galactooligosaccharide mixture (B-GOS) in healthy elderly volunteers. Am J Clin Nutr. 2008 Nov;88(5):1438-46.
Nakata A. Psychosocial job stress and immunity: a systematic review. Methods Mol Biol. 2012;934:39-75
Bauer M, Jeckel C and Luz C. The role of stress factors during aging of the immune system. Neuroimmunomoduation. 2009 1153: 139-152.
Pérez de Heredia F, Garaulet M, Gómez-Martínez et al. Self-reported sleep duration, white blood cell counts and cytokine profiles in European adolescents: the HELENA study. Sleep Medicine. 2014. 15 (1251-1258.
Walsh N, Gleeson M, Shephard R et al. Position Statement: Part One: Immune function and exercise. EIR. 2011; 17.
Li, Q. Effect of forest bathing trips on human immune function. Environ Health Prev Med. 2010; 15:9-17.
Bennett M, Zeller J, Rosenberg L et al. The effect of mirthful laughter on stress and natural killer cell activity. Alternative Therapies. 2003. 9 (2);38-44.