Dec. 18, 2003 DECEMBER 3, 2003 (Bethesda, MD) – How best to keep school aged children from getting sick? Some invoke the most famous parental warning of all: "Don't go outside with your hair wet or you'll catch pneumonia." Now, a new study offers additional strategies for combating the number of cold and flu symptom days among youngsters.
A report by Canadian researchers demonstrates that children who spent more time in sports activities and had higher aerobic fitness reported fewer "sick" days, and those with body fat higher than 25% reported significantly more such events. Their study also found evidence connecting reduced physical activity and excess body fat with higher incidences of upper respiratory tract infections (URTI).
A New Study
The investigation examines the relationships between mucosal immunity, physical fitness levels, stress levels, and relative body fat in 10- to 11-yr-old children attending public schools in Southern Ontario, Canada. Thomas J. Cieslak, Gail Frost, and Panagiota Klentrou from the Faculty of Applied Health Sciences, Brock University, St. Catharines, Ontario, CN, are the authors of the study, entitled "Effects of Physical Activity, Body Fat, and Salivary Cortisol on Mucosal Immunity in Children." Their findings appear in the December 2003 edition of the Journal Applied of Physiology. The Journal is one of 14 scientific journals published each month by the American Physiological Society (APS).
The researchers followed the protocol outlined below:
Subjects: Sixty-one fifth grade students (29 boys, 32 girls) from three randomly selected schools in Southwestern Ontario participated in the study, which was conducted in May and June. Any medication taken for treatment of illness was recorded.
Physical activity and fitness assessments: Predicted peak aerobic power was estimated and recorded. An estimate of each individual's peak O2 was also determined. A Habitual Activity Estimation Scale (HAES) was used to estimate the time spent in all forms of habitual activity, i.e., the number of hours of habitual physical activity per day. Total duration of daily activity was used to calculate the total weekly habitual activity (h/wk). A Participation Questionnaire was used to estimate both the amount of physical activity and the nature of the participation. Total distance traveled per day was measured using a pedometer.
Body fat measurements: Estimates were made of the participant's percent body fat by using the input variables of physical activity level, body frame size, height, mass, and gender.
Saliva testing. Subjects provided two saliva samples. After collection of the first sample, temperature of the subject was taken to ensure that cortisol contained in the second saliva sample was not affected by acute stress. SIgA in saliva was measured by radial immunodiffusion and results were expressed as a SIgA-to-Alb ratio (SIgA/Alb).
Frequency of URTI: A 1-mo health log was used to record the incidence and duration (number of days) of URTIs. Subjects recorded cold and flu symptoms each day of the month by using a set of codes provided with the log. The severity of the symptoms was rated by each subject as mild, moderate, or severe. Parental supervision was required to ensure accurate recording of the symptoms. All logs were completed during the April to June period, which is a moderate- to high-infection season for Canada. The total number of days with URTI symptoms was calculated for each subject, with days being counted only if 2 or more consecutive days of cold or flu symptoms were reported. A randomly selected subgroup (n = 15) was assessed a second time, 6 wk after initial testing.
Statistical analysis: One-way ANOVA was used to compare boys and girls on physical activity, percent body fat, aerobic power, SIgA, and salivary cortisol. Analysis was conducted to detect relationships among all the variables, and intraclass correlation analysis was used to test the reproducibility of resting salivary cortisol and IgA measures (before and 6 wk after). A minimum value of P 0.05 indicated a statistically significant result.
The researchers found that:
* while there were no statistically significant differences between genders found in physical characteristics, significant differences were found between genders in predicted peak O2 and in distance traveled per day;
* no significant difference was evident between genders in reported levels of physical activity and relative body fat and there was no significant difference between genders in either SIgA or SIgA/Alb;
* based on the HAES questionnaire, children who were active <3 h/day were considered hypoactive; those who recorded activity levels >3 h/day were considered active. Twenty-two percent of boys reported <3 h/day of habitual physical activity, whereas 31.8% of girls did not achieve this level. The hypoactive children had significantly lower predicted peak O2 and SIgA/Alb, as well as significantly higher relative body fat and frequency of URTI. Moreover, body fat values revealed that 40% of the children (50% of boys and 42% of girls) had relative body fat >25%. Children with relative body fat higher than 25% reported significantly more days with cold and flu symptoms and total sick days than the rest of the cohort;
* organized activity and free-time activity were significantly related to peak O2. The total activity score was significantly correlated with peak O2, distance traveled per day, and resting salivary cortisol levels. Distance traveled per day was also significantly correlated with peak O2, as well as with time spent in organized sport activities. Salivary cortisol was significantly correlated with body fat and time spent in organized sport. SIgA and SIgA/Alb demonstrated a significant relationship only with incidence of URTI. The incidence of URTI was also correlated with total activity score, weekly habitual activity, and resting salivary cortisol; and
* the intraclass correlation coefficient for initial and post-6-wk measures of salivary cortisol was r = 0.66. The intraclass correlation coefficients for SIgA and SIgA/Alb were r = 0.23 and r = 0.20, respectively. When the means were compared, initial and post-6-wk measurements of SIgA and SIgA/Alb were not significantly different.
This study demonstrates the importance of physical activity for children's resistance to infection. Children who spent more time in sport activities and had higher aerobic fitness reported fewer sick days, whereas children with relative body fat exceeding 25% reported significantly more sick days than the rest of the cohort. With this in mind, the new parental warnings should, perhaps, be modified to: "Don't go outside with your hair wet -- but do go out!."
Source: December 2003 edition of the Journal Applied of Physiology. The Journal is one of 14 scientific journals published each month by the American Physiological Society (APS).
The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.
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