For one thing, stress is difficult to define. What may appear to be a stressful situation for one person is not for another. When people are exposed to situations they regard as stressful, it is difficult for them to measure how much stress they feel, and difficult for the scientist to know if a person's subjective impression of the amount of stress is accurate.

The scientist can only measure things that may reflect stress, such as the number of times the heart beats each minute, but such measures also may reflect other factors. Most scientists studying the relationship of stress and immune function, however, do not study a sudden, short-lived stressor; rather, they try to study more constant and frequent stressors known as chronic stress, such as that caused by relationships with family, friends, and co-workers, or sustained challenges to perform well at one's work.

Some scientists are investigating whether ongoing stress takes a toll on the immune system. But it is hard to perform what scientists call "controlled experiments" in human beings. In a controlled experiment, the scientist can change one and only one factor, such as the amount of a particular chemical, and then measure the effect of that change on some other measurable phenomenon, such as the amount of antibodies produced by a particular type of immune system cell when it is exposed to the chemical.

In a living animal, and especially in a human being, that kind of control is just not possible, since there are so many other things happening to the animal or person at the time that measurements are being taken.

Despite these inevitable difficulties in measuring the relationship of stress to immunity, scientists are making progress. Almost every mother has said it: "Wear a jacket or you'll catch a cold!

Probably not, exposure to moderate cold temperatures doesn't increase your susceptibility to infection. There are two reasons why winter is "cold and flu season. Also the influenza virus stays airborne longer when air is cold and less humid. But researchers remain interested in this question in different populations.

Some experiments with mice suggest that cold exposure might reduce the ability to cope with infection. But what about humans? Scientists have performed experiments in which volunteers were briefly dunked in cold water or spent short periods of time naked in subfreezing temperatures.

They've studied people who lived in Antarctica and those on expeditions in the Canadian Rockies. The results have been mixed. For example, researchers documented an increase in upper respiratory infections in competitive cross-country skiers who exercise vigorously in the cold, but whether these infections are due to the cold or other factors — such as the intense exercise or the dryness of the air — is not known.

A group of Canadian researchers that has reviewed hundreds of medical studies on the subject and conducted some of its own research concludes that there's no need to worry about moderate cold exposure — it has no detrimental effect on the human immune system.

Should you bundle up when it's cold outside? The answer is "yes" if you're uncomfortable, or if you're going to be outdoors for an extended period where such problems as frostbite and hypothermia are a risk.

But don't worry about immunity. Regular exercise is one of the pillars of healthy living. It improves cardiovascular health, lowers blood pressure, helps control body weight, and protects against a variety of diseases. But does it help to boost your immune system naturally and keep it healthy?

Just like a healthy diet, exercise can contribute to general good health and therefore to a healthy immune system. As a service to our readers, Harvard Health Publishing provides access to our library of archived content.

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February 15, Helpful ways to strengthen your immune system and fight off disease How can you improve your immune system? What can you do to boost your immune system?

Photos courtesy of Michael N. Starnbach, Ph. Every part of your body, including your immune system, functions better when protected from environmental assaults and bolstered by healthy-living strategies such as these: Don't smoke.

Eat a diet high in fruits and vegetables. Exercise regularly. Maintain a healthy weight. If you drink alcohol, drink only in moderation. Get adequate sleep. Take steps to avoid infection , such as washing your hands frequently and cooking meats thoroughly. Try to minimize stress.

Keep current with all recommended vaccines. Vaccines prime your immune system to fight off infections before they take hold in your body. Increase immunity the healthy way Many products on store shelves claim to boost or support immunity.

Immune system and age As we age, our immune response capability becomes reduced, which in turn contributes to more infections and more cancer. Diet and your immune system Like any fighting force, the immune system army marches on its stomach. Improve immunity with herbs and supplements? Stress and immune function Modern medicine has come to appreciate the closely linked relationship of mind and body.

Does being cold give you a weak immune system? Exercise: Good or bad for immunity? Share This Page Share this page to Facebook Share this page to Twitter Share this page via Email.

Print This Page Click to Print. Related Content. Staying Healthy. You might also be interested in…. Acquired forms are more common and include AIDS and cancers like leukemia and multiple myeloma. Eating enough nutrients as part of a varied diet is required for the health and function of all cells, including immune cells.

Certain dietary patterns may better prepare the body for microbial attacks and excess inflammation, but it is unlikely that individual foods offer special protection.

Examples of nutrients that have been identified as critical for the growth and function of immune cells include vitamin C, vitamin D, zinc, selenium, iron, and protein including the amino acid glutamine.

Diets that are limited in variety and lower in nutrients, such as consisting primarily of ultra-processed foods and lacking in minimally processed foods, can negatively affect a healthy immune system. It is also believed that a Western diet high in refined sugar and red meat and low in fruits and vegetables can promote disturbances in healthy intestinal microorganisms, resulting in chronic inflammation of the gut, and associated suppressed immunity.

The microbiome is an internal metropolis of trillions of microorganisms or microbes that live in our bodies, mostly in the intestines. It is an area of intense and active research, as scientists are finding that the microbiome plays a key role in immune function. The gut is a major site of immune activity and the production of antimicrobial proteins.

A high-fiber plant-rich diet with plenty of fruits, vegetables, whole grains, and legumes appear to support the growth and maintenance of beneficial microbes. Certain helpful microbes break down fibers into short chain fatty acids, which have been shown to stimulate immune cell activity.

These fibers are sometimes called prebiotics because they feed microbes. Therefore, a diet containing probiotic and prebiotic foods may be beneficial. Probiotic foods contain live helpful bacteria, and prebiotic foods contain fiber and oligosaccharides that feed and maintain healthy colonies of those bacteria.

Animal studies have found that deficiencies in zinc , selenium , iron , copper, folic acid , and vitamins A , B6 , C , D , and E can alter immune responses.

Epidemiological studies find that those who are poorly nourished are at greater risk of bacterial, viral, and other infections. Eating a good quality diet, as depicted by the Healthy Eating Plate, can prevent deficiencies in these nutrients. However, there are certain populations and situations in which one cannot always eat a variety of nutritious foods, or who have increased nutrient needs.

In these cases a vitamin and mineral supplement may help to fill nutritional gaps. Studies have shown that vitamin supplementation can improve immune responses in these groups. The elderly are a particularly high-risk group.

The immune response generally declines with increasing age as the number and quality of immune cells decreases. This causes a higher risk of poorer outcomes if the elderly develop chronic or acute diseases.

In addition, about one-third of elderly in industrialized countries have nutrient deficiencies. Diet variety may also be limited due to budget constraints or lower interest in cooking for one person; poor dentition; mental impairment; or lack of transportation and community resources to obtain healthy food.

Megadose supplements many times the RDA do not appear justified, and can sometimes be harmful or even suppress the immune system e.

Remember that vitamin supplements should not be considered a substitute for a good diet because no supplements contain all the benefits of healthful foods. Several herbal supplements have been suggested to boost immune function. What does the research say?

Diet Review: Anti-Inflammatory Diet. Food Safety, Nutrition, and Wellness during COVID Ask the Expert: The role of diet and nutritional supplements during COVID The contents of this website are for educational purposes and are not intended to offer personal medical advice.

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Search for:. Home Nutrition News What Should I Eat? What Is Our Immune System? These barriers include: Skin that keeps out the majority of pathogens Mucus that traps pathogens Stomach acid that destroys pathogens Enzymes in our sweat and tears that help create anti-bacterial compounds Immune system cells that attack all foreign cells entering the body Adaptive or acquired immunity is a system that learns to recognize a pathogen.

Other conditions that trigger an immune response Antigens are substances that the body labels as foreign and harmful, which triggers immune cell activity. What factors can depress our immune system? Older age: As we age, our internal organs may become less efficient; immune-related organs like the thymus or bone marrow produce less immune cells needed to fight off infections.

Aging is sometimes associated with micronutrient deficiencies, which may worsen a declining immune function. Environmental toxins smoke and other particles contributing to air pollution, excessive alcohol : These substances can impair or suppress the normal activity of immune cells.

Excess weight: Obesity is associated with low-grade chronic inflammation. Fat tissue produces adipocytokines that can promote inflammatory processes.

Chronic diseases: Autoimmune and immunodeficiency disorders attack and potentially disable immune cells. Chronic mental stress: Stress releases hormones like cortisol that suppresses inflammation inflammation is initially needed to activate immune cells and the action of white blood cells.

Lack of sleep and rest: Sleep is a time of restoration for the body , during which a type of cytokine is released that fights infection; too little sleep lowers the amount of these cytokines and other immune cells.

Does an Immune-Boosting Diet Exist? Probiotic foods include kefir, yogurt with live active cultures, fermented vegetables, sauerkraut, tempeh, kombucha tea, kimchi, and miso. Prebiotic foods include garlic, onions, leeks, asparagus, Jerusalem artichokes, dandelion greens, bananas , and seaweed.

However, a more general rule is to eat a variety of fruits, vegetables , beans , and whole grains for dietary prebiotics.

Chicken soup as medicine? Is there scientific evidence that it aids in healing? But when breaking down its ingredients, it does appear a worthwhile remedy to try.