intervals of breastfeeding, but also include worries regarding risks of overfeeding
their babies in the face of augmenting rates of childhood obesity with attendant
lifelong implications for health (Reilly and Kelly 2011 ). Clarifications of infant
nutritional needs surrounding growth spurts is a significant area for further research.
Sleeping
He’s awake to eat and have his diaper changed then back to sleep he goes...apparently
growth spurts are tiring!Amidst the sleep deprivation that characterizes thefirst few months of parent-
hood (Rudzik and Ball, this volume), a child’s sudden hibernation evokes both
curiosity and worry. Cyclic patterns of active and quiet sleep begin developing
prenatally (Peirano et al. 2003 ), but undergo much variation as the infant matures
during thefirst six months of life (Coons and Guilleminault 1982 ). Lampl and
Johnson (2011a) empirically demonstrated that peaks in total daily sleep hours
predict body length saltation events. The sudden need for more sleep may reflect
alterations in the hormonal milieu that facilitates a growth spurt, and more
specifically, may relate to upregulation of growth hormone (GH) secretion
(Finkelstein et al. 1971 ).
Growth hormone has long been recognized to play an integral role in postnatal
growth (Butler and Le Roith 2001 ; Kaplan and Cohen 2007 ). A peptide hormone
secreted from the pituitary gland GH initiates chondrocyte proliferation at the
epiphyseal growth plate by stimulating insulin-like growth factor 1 (IGF-1)
secretion (Nilsson et al. 2005 ; Pass et al. 2009 ). Interacting with a complex network
of local and systemic growth factors, hormones, and other compounds in the
extracellular matrix, IGF-I autocrine, and paracrine signaling stimulates chondro-
cyte clonal expansion and hypertrophy, steps necessary for bone accrual (Mackie
et al. 2011 ; Wang et al. 1999 ). Greater secretory pulses of GH have been
demonstrated after the onset of slow-wave sleep (stages 3 and 4) (Holl et al. 1991 ),
with the amount of GH secreted concordant to the amount of time spent in
slow-wave sleep (Van Cauter and Plat 1996 ). Thus, sleep is inherently connected to
the biology underlying growth events by modulating GH production and exposure.
Longitudinal research conducted among pre-pubertal children measured thrice
weekly demonstrated this relationship, finding that irregular patterns of GH
secretion were associated with height growth rate (Gill et al. 2001 ). While sleep
durations were not assessed in this study, the observation suggests that the variation
in sleep schedules among infants is a normal physiological process that moderates
exposure to GH, with the extended sleep hours surrounding growth events (Lampl
and Johnson2011a), providing a means to enhance chondrocyte activity and, in
turn, bone deposition.
4 The Lived Experience of Growing 57