Longer breastfeeding is associated with increased lower body explosive strength during adolescence

Journal Title (Medline/Pubmed accepted abbreviation): J Nutr
Year: 2010
Volume: 140
Page numbers: 1989-1995
doi: 10.3945/jn.110.123596

Summary of Background and Research Design

Background:Extensive research supports multiple advantages of breastfeeding in humans. For infants, the benefits include health and nutritional needs, immunologic function, and physical, cognitive, psychological, and social development. In addition, breastfeeding has important implications for maternal psychological status and provides economic and environmental benefits. It has been suggested that perinatal factors, such as breastfeeding, may influence physical fitness and body composition, which are 2 important markers of health throughout life. Although the association between breastfeeding and body composition has been widely studied, the relationship is still not fully understood. Additionally, there is little research examining the effect of breastfeeding on later physical fitness.

Hypothesis/purpose of study: To examine the association between breastfeeding duration and cardiorespiratory fitness, isometric strength, and explosive strength during adolescence

Subjects:Adolescents (N = 2,567: 1,141 boys and 1,426 girls) age 12.5 to 17.5 years with valid data for sex, body mass index (BMI), breastfeeding, and gestational age were included in the study.

Experimental design: Retrospective

Treatments and protocol: This report is based on data derived from the Healthy Lifestyle in Europe by Nutrition in Adolescence cross-sectional study (HELENA), which aims to obtain standardized, reliable, and comparable data on relevant nutrition and health-related markers from a random sample of European adolescents. Data collection took place during 2006 and 2007 in 10 European cities. A parental questionnaire was developed to collect information on adolescents’ birth weight and height, gestational age, and duration of breastfeeding. Parents were asked about the duration of exclusive breastfeeding, defined as feeding exclusively breast milk with no fluid or solid complementary food. Breastfeeding duration was coded as never, < 3 months, 3 to 5 months, and ≥ 6 months. Physical fitness was assessed in the HELENA Study with the 20-m shuttle run, handgrip strength, and standing long jump tests. Weight, BMI, body fat percentage, and fat-free mass were collected and further classified as above or below the sex-specific medians. Sexual maturation was assessed by a medical doctor and graded stages I-V. Significant differences among the categories of breastfeeding duration were tested after adjusting for a set of potential confounders including gestational and current age, birth weight, sexual maturation, fat mass, fat-free mass, maternal education, parental weight status, country, smoking behavior, and days of vigorous physical activity.
Summary of research findings:
  • 28.1% of European adolescents had been breastfed for ≥ 6 months, with no significant differences between sexes (27.7% in boys and 28.5% in girls).
  • Duration of any breastfeeding (either any or exclusive) was positively associated with performance in the standing long jump test in both boys and girls (P < .001), regardless of any of the potential confounders.
  • Handgrip strength was unaffected by duration of breastfeeding.
  • Duration of any breastfeeding was also associated with the 20-m shuttle run test in girls (P < .01), yet this association did not show a clear dose-effect regarding the duration of breastfeeding.
  • In adolescents who were breastfed for 3 to 5 months or ≥ 6 months, the risk of having a standing long jump performance below the 5th percentile was reduced by half compared with those who were never breastfed (odds ratio [OR] = 0.54; 95% CI = 0.30, 0.96; P < .05; and OR = 0.40; 95% CI = 0.22, 0.74; P < .01, respectively).
  • When exclusive breastfeeding was used as the predictor variable instead of any breastfeeding, the results were virtually identical except for the association between breastfeeding and the 20-m shuttle run test in girls, which became nonsignificant.
  • The results were not altered when sexual maturation status was entered into the model instead of age.

Interpretation of findings/Key practice applications:

The main finding of this study was that the duration of either any or exclusive breastfeeding was positively associated with lower body explosive strength regardless of fat mass or fat-free mass and a complete set of potential confounders. The duration of breastfeeding was also significantly associated with cardiorespiratory fitness in girls, although there was not a clear direction for this association and it disappeared with exclusive breastfeeding. This study is limited by the design, which required a retrospective analysis. Further, although these analyses included the detailed information available on individual and family characteristics to adjust for factors that potentially confound the relationship of breastfeeding with health status later in life (gestational age, birth weight, body composition, socioeconomic status, parental weight status, and the adolescent’s smoking behavior and physical activity), there is still the possibility of an unrecognized confounder. In addition, based on the nature of the data collected, there may be limitations in the ability of the authors to fully assess the effects of the confounders they did identify. For example, it is not clear if “days of vigorous physical activity” is an appropriate marker of the duration and intensity of exercise. It also might not fully tease out the participation in sports programs in which children not only exercise, but receive coaching and drills to improve neuromuscular coordination. Overall, these findings suggest a role of early infant feeding patterns in determining muscular fitness later in life, supporting the continued promotion of breastfeeding. However, this is a very preliminary finding and more research is required before definitive conclusions can be drawn.
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