The health of the cardiovascular system is associated with the fitness level of the cardiorespiratory system. In other words, for a given age both children and adults are considered to have improved cardiovascular health with increase cardiorespiratory fitness, although the relationship is not linear. Recent scientific research suggests that the nutrition intake of the developing foetus and neonatal infant are strongly associated with later disease risk. Detailed understanding of early nutrition is increasingly being seen as important in predicting the spectrum of lifestyle diseases that emerge in adulthood. Breast feeding is associated with a reduction in the risk of cardiovascular disease and is thought to be protective of obesity in later life. The association between cardiorespiratory fitness and cardiovascular health suggests that breast feeding may play a role in both. Scientists are interested in understanding this link between duration of breast feeding and cardiorespiratory fitness in later life.
For example, researchers1 have investigated the association between breastfeeding duration and cardiorespiratory fitness in children and adolescents. Subjects (n=1996) from the Estonian and Swedish part of the European Youth Heart Study were categorised as either exclusively breast fed or exclusively formula fed for <3, 3-6 or >6 months. Cardiorespiratory fitness was assessed by a maximum cycle ergometer test in 1025 children (mean age 9.5 years) and in 971 adolescents (mean age 15.5 years). The results showed that breastfeeding for longer periods was associated with higher cardiorespiratory fitness, an association that remained significant even after adjustment for confounding variables such as fat free mass, bodyweight, education level and birth weight. These results therefore suggest that nutrition during early life plays a significant role of future cardiorespiratory fitness and that modification to the feeding patterns of infants may allow changes in future cardiorespiratory fitness levels.
Only two other studies have measured the association between infant feeding and fitness, with one finding similar improvements in cardiorespiratory fitness on a cycle test and one finding improvements in standing long jumps. The finding that future cardiorespiratory fitness was most highly associated with infants from the upper tertile of birth weight is not surprising as higher birth weight is associated with longer duration of breastfeeding, higher cardiorespiratory fitness and higher fat free mass. In general, exclusive breastfeeding as an infant was associated with ~5.3% increase in cardiorespiratory fitness levels as measured by VO2 max (L/min). Normalising the effect to take into account body weight reduced the fitness increase to ~3%. However, the authors did suggest that because of the lack of a known mechanism by which breast feeding could decrease cardiovascular risk or improve cardiorespiratory fitness, care should be taken when assigning cause and effect.
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