Can Exercise Prevent Colds in Kids?

Preschoolers have between six and eight colds per year, while adults typically have two to three. When young children feel lousy, families also suffer reduced quality of life. The burden of illness can cause worry, trips to the doctor, lost time from work, and disruptions to school, sports, and other activities for older siblings. Can physical activity reduce the number of sick days? What about the severity of the illness? New research among preschoolers suggests that children who tend to be the least active may benefit the most from getting more active.

Upper respiratory tract infections (URTIs) are common among children, especially preschoolers, who are still developing immunity to common viral and bacterial infections. Although most episodes of illness resolve on their own, recurrent infections cause the child to be uncomfortable and may distress the parent.

When illnesses run through the family, they often disrupt school, work, and family life. Childhood illnesses are also a substantial contributor to urgent care clinic and emergency department visits, resulting in a high burden on the health care system.

The most common illness-inducing pathogens among children are rhinoviruses, respiratory syncytial virus (RSV), influenza and parainfluenza, and seasonal coronaviruses, which now include SARS-CoV-2. A recent UK study of children who frequently visit the emergency department found that URTIs accounted for approximately a third of all visits.

Why are children so susceptible to colds?

The number of colds decreases with age. This is because young children need time to build up immunity, and immunity is often won the hard way — by being exposed to and fighting off infections. As the body is exposed to viruses and bacteria in the community, we develop specific antibodies which can protect us in the future.

However, immunity can also be built through vaccination, such as for polio, measles, mumps, rubella, diphtheria, tetanus, pertussis, pneumococcal pneumonia, chickenpox, and rotavirus. The CDC also recommends influenza and COVID-19 vaccines for children.

Exercise & reduced cold symptoms

A recent study published in Nature considered whether physical activity could reduce the number of days with cold symptoms among young children ages four through seven years. Interestingly, this study required preschool attendance as one of the inclusion criteria. This means that the findings are relevant even to those children at higher risk for URTIs.

Children were not eligible for the study if they had a chronic underlying medical condition such as immune suppression, severe respiratory diseases, allergies, or lower respiratory symptoms.

The children were given a Garmin step counter to wear 24/7 for 40 days, and parents recorded the presence or absence of cold symptoms every day for 60 days. In addition, there was a two-week run-in period at the beginning of the study to measure the baseline physical activity levels of the children.

The researchers reviewed the activity levels and sleep duration of the 104 children who completed the study and correlated these findings with the symptom questionnaires.

The median number of days with a URTI symptom was 26 days, so approximately half of the 60-day study period, confirming the universal burden of cold symptoms among most preschool-age children. The most common symptoms were a runny nose and cough.

There were no statistically significant differences in the number of symptom days according to sleep duration, siblings, vaccination status, exposure to pet hair, or smoking.

On the other hand, fewer symptom days were found to be correlated with average daily step count (p<0.001) and participation in a sport (p=0.021). It did not appear to matter whether the child’s physical activity was intense or not — what seemed to matter was being active. The range of step counts was 3,000 to 12,000 per day, with a strong correlation between more steps and fewer symptom days.

The investigators created a regression model to estimate the mathematical relationship between 1000 extra steps per day and the number of sick days while holding all the other variables constant. They found that 1000 fewer average steps per day were associated with 4.1 more total URTI symptom days.

Severity of symptoms linked to step counts

The study team also looked at the severity of symptoms by step count and whether the child participated in a sport. Here they found a striking difference in how the children rated the severity of their symptoms: the non-sport children reported a much lower severity score with increased step counts, but the severity scores were uniformly low among children in sports regardless of their daily step count.

Does this mean increasing daily steps will reduce the number of sick days by four or reduce symptom severity? Not necessarily. It could be that more active children tend to ignore minor symptoms like a runny nose. However, the researchers attempted to answer this by dividing the study group into more-active and less-active children according to their baseline run-in period. They still found an association between activity and the number of days with the illness.

How does this research compare to what we know already?

This is a compelling study because it uses a valid tool to measure activity and sleep data 24/7 and validated questionnaires specifically designed to collect symptom days. Perhaps most importantly, the entire study population lives in an urban area (Warsaw) and attends preschool, controlling for two established risk factors (air pollution and daycare attendance).

"Exercise is important to not only immune function but also cardiovascular disease, pulmonary function, mental health, and even self-esteem, <…> Establishing a pattern of regular exercise for your child pays dividends now and later in life. It is a gift that keeps on giving throughout a child’s life, as behaviors in childhood often carry into adulthood."

Daniel Johnson, MD, Professor of Pediatrics at the University of Chicago School of Medicine.

The biological mechanism explaining the link between activity and immunity is not fully understood yet. However, it is thought that exercise stimulates the immune system, perhaps through cytokine induction and specialized antibodies lining the airways of the nose and mouth.

These mucosal membranes covering the upper airways are the first line of defense against everything we eat and breathe. Secretory IgA (SIgA) is the antibody that specializes in covering these mucosal membranes. While vaccines cannot yet induce SIgA, immune memory following infection does elicit antibody production.

Although most children ages four to six do not get the World Health Organization (WHO) recommended 10,000–14,000 steps per day, this study shows that benefits can accrue at any level of activity. Parents may find that these data are motivational enough to encourage physical activity for the whole family.

Adults looking for a good reason to track steps can also expect to benefit from physical activity. A systematic review and meta-analysis of 16 studies published in the British Journal of Sports Medicine reported that regular physical activity is related to a lower likelihood of adverse COVID-19 outcomes. You do not have to be an extreme sports enthusiast to benefit from the fresh air, vitamin D, improved cardiovascular health, and better mental health and sleep quality associated with increased activity.

Ways to increase physical activity daily

• Take your dog for an extra walk
• Make a walk-and-talk appointment to catch up with a friend or family
• Walk the parking lot at lunch
• Walk to a bus stop a little further from your home
• Take the stairs
• Stop driving to the school bus stop and walk with your child

“The study out of Poland provides more data to support the importance of activity to our immediate health and well-being,” Dr. Johnson adds. “In the era of COVID-19, many schools ask children with symptoms to stay home. This means reducing the number of days with cold symptoms is even more important — kids lose fewer days of school.”

What are some ways that you have increased the physical activity of your family? Join the conversation by adding some ideas in the comments below.