Exclusive Breastfeeding Is Favorably Associated with Physical Fitness in Children

Introduction

Physical fitness (PF) is defined as the “ability to carry out daily tasks with vigor and alertness, without undue fatigue and with ample energy to enjoy leisure-time pursuits and to meet unforeseen emergencies.”¹ As PF is a powerful marker of cardiovascular health in children, it is considered that a sufficient level of PF in childhood is needed to carry forward favorable behavioral and biological effects into later life.² Epidemiologic findings have proposed that improvement in PF is associated with a healthier life in children, in a dose–response fashion.³ On the contrary, low levels of PF in children are related to numerous risk factors such as hyperlipidemia, hypertension, and obesity.³ Moreover, a meta-analysis has shown that the relative risk for cardiovascular disease was higher among those who were below the 25th percentile of the PF distribution compared with those in higher percentiles.⁴ PF is influenced by numerous factors such as biological, genetic, environmental and lifestyle factors, as well as breastfeeding.^3–7

According to the World Health Organization, breastfeeding is the natural approach of providing infants with the needed nutrients for healthy growth and development.⁸ Specifically, exclusive breastfeeding is recommended for the first 6 months of life, followed by sustained breastfeeding for the first year of life and longer.⁹ Numerous international organizations have been paying attention towards enhancing the initiation, continuance, and exclusivity of breastfeeding.¹⁰ Exclusive breastfeeding is influenced by a complex of factors such as psychological, sociocultural, demographics, biomedical, health care system, and social support.^11–13 Among the potential risk factors for avoiding exclusive breastfeeding are maternal age and obesity status, maternal education, excessive gestational weight gain (GWG), parity before, nationality, infant characteristics, etc.^12,13 The favorable effects of breastfeeding on infant health include protection against common diseases and cardiovascular disease risk factors such as obesity, hypertension, and diabetes mellitus during childhood, neuropsychological benefits, enhanced motor development, etc.^14–19 Moreover, it has been proposed that human milk components, such as polyunsaturated fatty acids, adipokines, and prostaglandin J2, could explain the beneficial effects of breastfeeding on cardiorespiratory fitness (CRF).²⁰

However, to the best of our knowledge, few studies have examined the potential effect of exclusive breastfeeding and its duration on PF in children, while most of them have focused only on the effect of breastfeeding on CRF.^21–24 Specifically, two studies have proposed that a longer period of exclusive breastfeeding is associated with a favorable effect on CRF in children.^21,22 On the contrary, other researchers could not confirm the previous findings since they did not find a significant association between breastfeeding duration and CRF in children.^23,24 Furthermore, results from a study among European adolescents have shown that longer breastfeeding is connected with better lower body explosive strength.²⁴

From the public health aspect, because early infant feeding practices are possibly modifiable, it is essential to better understand the potential programming effect of breastfeeding on PF. This information could further support the development of health interventions to increase exclusive breastfeeding.

Thus, we aimed to examine the effects of exclusive breastfeeding and its duration on PF components such as CRF, muscular strength of upper and lower body, speed, and agility in a large, representative cohort of Greek children 8–9 years old, taking into consideration several potential confounders.

Materials and Methods

Study design

Population-based data were derived from 10 national school-based health surveys, following an official request to the Greek Ministry of Education. The national database included anthropometric data and information on age, gender, city and area, home address, and telephone number, which were collected yearly during the specific time period (spring) from 1997 to 2007, with the exception of 2002, in almost all schools of primary education (roughly 85%); schools that did not participate were from borderland areas, with small numbers of children. Thus, from 1997 to 2007, a total of 651,582 eight- to nine-year-old children (51% boys and 49% girls, over 95% of the total student population) participated in the study. Measurements were performed by two trained physical education (PE) teachers in each school. PE teachers followed a specific protocol taught to them during corresponding seminars held by the Greek General Secretariat of Sports. The same protocol was employed in all schools.

Data extraction

A sample of 5,500 children (0.8% of the entire population) was randomly extracted from the database and their mothers were contacted via telephone. Random extraction was performed using a statistical software. The number of 5,500 subjects was adequate to achieve statistical power ≥99% for evaluating a 0.10 ± 0.05 change in regression coefficients at 5% significance level of two-sided tested hypotheses. The random sampling was stratified based on the region and place of living (e.g., rural/urban), according to the National Statistical Agency and equally distributed during the study period (i.e., 500 mothers per year). The women who refused to participate in the study were 183 (3.3%). The sample of mother–child dyads covered all geographical regions of Greece (e.g., mainland Greece and the islands). The information of the proposed protocol was collected through telephone interviews based on the computer-aided telephone interview method. To validate the process, 100 face-to-face interviews were conducted to check for discrepancies with the information collected via telephone. No such discrepancies were noted in any of the variables evaluated.