Exercise as it relates to Disease/The effects of moderate to vigorous physical activity on the risk of upper respiratory tract infections

The following Wikibooks page is an analysis of 'Moderate to vigorous physical activity and risk of upper-respiratory tract infection' a study published in 'Medicine & Science in Sport & Exercise (March 2002) CHARLES E. MATTHEWS, IRA S. OCKENE, PATTY S. FREEDSON, MILAGROS C. ROSAL, PHILIP A. MERRIAM, and JAMES R. HEBERT.

What is the background to this research?
Upper-respiratory tract infections (URTI's) are Widely acknowledged to be among the most common types of infections contracted by humans. Per year the average adult suffers from between 2 and 5 URTI's such as the common cold and influenza. A J shaped model is commonly used to describe the relationships between physical activity and the level of risk of contracting a URTI, this suggests that the lowest risk of contracting a URTI is found in people that are moderately active, while people that participate in a high level of physical activity or are physically inactive are at a significantly higher risk.

However, there is a lack of epidemiologic data that supports the connection between moderately active individuals and a lowered risk of contracting a URTI. URTI's are the leading cause of physician visits and days missed of work This study aims to create a better understanding of the relationship between physical activity and the risk of contracting URTI's.

Where is the research from?
This Study was conducted by Charles E, Matthews, Ira S. Ockene, Patty S. Freedson, Milagros C. Rosal, Philip A. Merriam and James R. Herbert in the department of epidemiology and biostatics at the University of South Carolina and was published in Medicine and science in sports and exercise, which is the American College of Sports Medicines flagship monthly peer reviewed journal.

Although the study took place in Carolina, USA. The research results are relevant to the Australian demographic.

Charles E Matthews is a physical epidemiologist and investigator in metabolic epidemiology and has published a number of papers on the relationships between physical activity and human conditions. The other authors have published multiple papers relating to physical activity

What kind of research was this?
This was a observational study of 547 healthy participants (49% women) aged 20-70yrs. URTI events were reported over 12 months in 90 day intervals, 3 24 hour physical activity recalls per 90 day interval were obtained to quantify total moderate physical activity.

The relationships between URTI's and physical activity levels were estimated using incidence rate ratios while being adjusted based on a number of factors such as age, education, anxiety, cynicism and dietary factors.

What did the research involve?
Participants at the baseline of the study and also in each of the four follow up periods (90 days) were required to provide blood samples and have their body mass (BMI) measured in a clinic.

Demographic data such as age, gender, marital status, employment as well as health habits (smoking and multivitamin usage) were recorded through self-administrated questionnaires at the beginning of the study.

Physical activity assessment was conducted though 15 24 hour recalls where participants recalled the number of time, they spent in each of the four exercise intensities (light, moderate, vigorous, very vigorous). Light exposure and diet data were collected using 24 hour recalls at the end of each of the 90-day intervals surrounding each clinic visit, these were conducted through unannounced telephone-administrated interviews on 3 randomly selected days throughout the week. Data regarding URTI's such as the number colds, flus or allergic episodes were recorded at each of the 90 day clinic visits.

Strengths of the study's methodology:

- An observational longitudinal study with a large cohort and a wide variety in demographic over a long period of time spanning the various seasons throughout the year provides a strong foundation for the study.

- In person clinic meet ups every 90 days as well as randomized telephone interviews throughout the 90-day period.

- 4 levels of physical activity intensity (light, moderate, vigorous, and very vigorous)

- Recording the data in 90-day periods allows the data to reflect the various seasons throughout the year and allows for comparisons between winter and summer URTI rates.

Participants physical activity and URTI data were primarily recorded through self-reporting which has been shown to be somewhat inaccurate due to over/under reporting of physical activity compared to other methods such as motion monitors (GPS watch, Fitbit)

Low number of individuals completing very vigorous activity levels limiting their ability to affectively evaluate the relationship between very vigorous activity levels and URTI's

What were the basic results? What were the important findings?
The results of the study support the hypothesis of the J shaped relationship between physical activity levels and the risk of contracting a URTI. The results demonstrate that high levels of moderate vigorous activity were associated with a 20-30% reduced risk of URTI annually with a majority of the reduction in risk being realized in the summer and fall months. URTI events were reported highest in the winter and fall with approximately 40% of the participants reporting a URTI, compared to only 10% in the summer. Having a stronger effect in men than women.

In further analysis demographic and other factors such as BMI, smoking history, vitamin supplementation, occupation and leisure that were recorded did not affect URTI risk.

The researchers did acknowledge the limitations of an observational study that heavily relies on self-reports of URTI's and physical activity levels although found that their results mimicked results from various other studies that utilized more invasive assessment methods. Lack of participants completing in high levels of vigorous activity limits the studies ability to produce a meaningful conclusion on high levels of vigorous activity on URTI risk.

What conclusions can we take from this research?
The findings within this analysis demonstrate the beneficial relationship between moderate levels of vigorous activity and healthy immune system function. The research strongly supports the hypothesis of the J shaped relationship demonstrating the best benefit in moderate levels rather than low or high levels which show to increase the risk of URTI's.

The results of the study align with various other papers published on this subject although most seem to be limited by their lack of control groups. Due to the large scale of the study the reliance on self-reporting is increased. Only a small percentage of the participants completed a significant amount of very vigorous exercise making it difficult to compare results.

Practical advice
URTI's are the most common illness suffered by humans presenting a huge strain on the economy reportedly costing the U.S $40 billion and Australia $7 billion a year through missed days of work and public health subsidies

The results from this research demonstrated the relationship between different levels of physical activity and the risk of URTI's. Encouraging the population to participate in moderate levels of vigorous (3.0 - 5.9 MET's) could significantly reduce the burden of URTI's on the economy. The Australian Government Department of Health recommendations are for adults to accumulate 2.5-5 hours of moderate (swimming, walking) and 1.25 -2.5 hours of vigorous intensity (jogging, cycling) or an equivalent combination of both each week.

Further information/resources

 * Physical activity and exercise guidelines for all Australians https://www.health.gov.au/health-topics/physical-activity-and-exercise/physical-activity-and-exercise-guidelines-for-all-australians
 * Flu costs Australian employers $7 billion in lost productivity https://thesector.com.au/2019/02/27/flu-costs-australian-employers-7-billion-in-lost-productivity/