Exercise is one of the best ways to show your body some TLC. Not only can it boost your mood and self-confidence, but a regular workout routine is key in the prevention of heart disease and can help keep the sniffles and sneezes away — just as long as you don't go overboard.
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1. Exercise Boosts Immune Cell Function
Here's what happens when you head out for a 30-minute walk: Muscle movement and an increased heart rate prompt immune cells to come out of their holding spots (e.g. lungs, spleen, lymph nodes), says David Nieman, DrPH, FACSM, a biology professor at Appalachian State University in Kannapolis, NC, and an exercise immunology researcher.
Because of that walk, there are more immune cells — natural killer (NK) cells and macrophages, specifically — circulating, primed and ready to seek and destroy pathogens. This effect is short-lived, but it adds up over time to strengthen your body's defenses, something that Nieman wrote about in May 2019 paper published in the Journal of Sport and Health Science.
Exercising 30 to 60 minutes a day is enough to trigger this immune response, Nieman says. Compared to staying sedentary, "our data show that this amount of exercise decreases sick days up to 50 percent," he says, citing his research published in April 2011 in the American Journal of Lifestyle Medicine. A May 2017 study from PLOS One came to a similar conclusion that less active people reported more sick days.
2. Heavy Breathing Ultimately Helps You Breathe Better
Cold and flu season is rough, but staying active can make it easier to stay healthy. "Regular exercise has been shown to flush bacteria out of lungs and reduce respiratory infections," says Purvi Parikh, MD, an expert in infectious disease, allergy and immunology with NYU Langone Health in New York City and the Allergy & Asthma Network.
3. Exercise Helps Reduce the Risk of Chronic Conditions, Too
Moving your body also helps keep stress hormones at bay. (What's a better way to simmer down after a tough day than a walk outside?) This, in turn, can help protect you from diabetes, which is key, as the disease can leave you more vulnerable to getting sick in the first place, Dr. Parikh says.
4. But Too Much Exercise Has the Opposite Effect
The reality with exercise is that more isn't always better. Consistently exercising too much can result in overtraining, which suppresses immune function and increases the likelihood of contracting an upper respiratory tract infection, according to a September 2012 review published in Sports Medicine.
Even pushing yourself to extremes in a single session can have negative effects. "The human body wasn't designed for high-intensity exercise that lasts for several hours," Nieman says. As your body uses up glycogen (essentially, carbohydrate stores) during activity, stress hormones are released, sending your immune system into "red flag mode," he says.
So if you're hoping to start an exercise program in the hopes of bolstering your immune system, be strategic about it and don't burn out on day 1. Ease into things. Remember: Most of the research points to positive correlations between consistent exercise and improved function, as opposed to one, all-out sweat session.
Read more: The Best Way to Avoid Getting Sick Is to Wash Your Hands — But You're Probably Doing It Wrong
How to Stay Healthy When You Exercise
1. Work Smarter. If you're training for a race, getting set up with a well-thought-out plan can ensure that you're ramping up duration and intensity appropriately, building in adequate rest and balancing hard and easy days.
"If you don't take adequate rest or recovery days to reduce inflammation [from a difficult bout of training], you can injure yourself and ironically suppress your immunity by putting too much stress on your immune system and body, setting yourself up for illness and infection," Dr. Parikh says.
2. Reduce Stress. Other factors can compound the immune-depleting effects of heavy training or an intense race, including lack of sleep, high mental stress and travel, Nieman says.
"Find the sweet spot where you can balance all of life's responsibilities with exercise," he says. "The number one reason to exercise is for your health, and if you exercise too much, you've defeated the health angle of it all."
This "sweet spot" will be different for everyone — listen to your body. If you sign up for an athletic event that requires you to train for longer periods of time (more than 90 minutes of sustained activity), reducing the stress from other sources in your life is even more important in order to stay well.
3. Skip if You're Sick. Don't push through a workout if you're under the weather — even if it's on your calendar and you're worried about missing it. "If you are sick with a cold, flu or infection, avoid exercise until you are back to good health," Dr. Parikh says. Otherwise, the added stress will prolong healing and recovery.
4. Protect Yourself. If you're in the middle of an intense period of training or you have a marathon on your calendar, make sure you've gotten your flu or pneumonia shots (as appropriate) and know that good hygiene practices are more important than ever. That means washing your hands before eating and after going to the bathroom and trying to avoid touching your face.
- Journal of Sport and Health Science: The compelling link between physical activity and the body's defense system
- American Journal of Lifestyle Medicine: Moderate Exercise Improves Immunity and Decreases Illness Rates
- Journal of Sports Medicine and Physical Fitness: Infectious Episodes in Runners Before and After the Los Angeles Marathon
- Sports Medicine: Overtraining, Excessive Exercise, and Altered Immunity