The results of this study indicated that group 1 (stunted) showed lower cognitive, motor, social emotional and adaptive behavior Bayley-III scores than group 2 (malnutrition with normal stature). The difference was mainly on motor aspect. Although these differences were not significant, these results were sufficient to show that stunted children showed lower developmental scores. Although group 2 not yet stunted but also showed score below P50 in all developmental scores. This also showed that stunting has not yet occurred, but cognitive impairment has happened.
Questions that always arise are why and how malnutrition and stunting affect brain development, especially cognitive; what are the long-term effects on a child's quality of life. The development of child’s brain in the first 1000 days of life is very important. Brain volume develops rapidly since fertilization, at birth reaching 25% of adult brain volume (400 grams), age 1 year reaches 60% (850 grams), age 2 years reaching 80% (1100 grams), until finally age 12 years child's volume brain and weight is the same as an adults.8 This means that during this time pregnant women need good nutrition for fetal brain development. In addition to brain volume and weight, synapses formation also accelerated. The synapse density of children aged 2 years is almost the same as adults.9
After birth, especially until the age of 2 years, the brain development process is still running especially brain volume and weight, the process of synaptogenesis, myelinogenesis and branching of dendrites and axons. Cognitive function is closely related to the formation of myelin and synapses. Myelin functions as an axon wrapper which speeds up the delivery of information flow between neuron cells. Synapse is a connection between neuronal cells where neurotransmitters are released in the gaps that regulate all functions of the human brain. The more dense the more synapses connection between neuron cells are also getting faster and more complex. Branching dendrites that function as recipients of information from other neuron cells are also important. 9
The acceleration of growth and development certainly requires good nutrition, both in quality and quantity. Carbohydrates are needed as a source of energy, cellular metabolism and the formation of brain structures globally. Proteins are needed for the formation of hippocampal structures, synaptogenesis (especially essential amino acids for the formation of neurotransmitters), synthesis of growth factors and cell proliferation and differentiation. Fat is needed for the formation of myelin and synapses, as well as the visual cortex. Micronutrients (vitamins and minerals) are needed mainly for cell metabolism, synapse formation and myelin.10
Malnutrition due to inadequate intake of protein, carbohydrates, fats and micronutrients as well as repeated infections can cause impaired brain function and structure, tissue damage, growth retardation, impaired cell differentiation, reduced synaptic and neurotransmitter formation, delayed myelination and overall reduction in dendritic branching development, and interferes with the formation of neuronal circuits. Eventually, chronic malnutrition that causes stunting and wasting will result in delays in the development of cognitive processes and permanent cognitive impairment.11
A study of two groups of children with a history of malnutrition, when carried out cognitive tests at the age of 5-7 years and 8-10 years. The group with a history of malnutrition showed cognitive scores (selective attention with color cancellation test, executive function, visuospatial function, verbal and visual memory), language function (verbal comprehension, verbal learning) was lower than the group that had never experienced malnutrition during the test. There were improvement in the scores when the test was repeated at the age of 8-10 years, although it remained lower than the group without malnutrition. This showed that stunted has more effect on higher cognitive functions than cognitive disorders and can be settled. 12
A study involving 5771 infants showed that children who experienced weight faltered from birth to 9 months had a significantly lower intelligence quotient (IQ) score (2.71 points) at 8 years of age. Weight gain from birth to 8 weeks has a positive correlation with IQ at 8 years of age while weight gain from 8 weeks to 9 months does not have a linear correlation with 8 years old IQ. It was concluded that failure to thrive in infancy is associated with a permanent IQ deficit at the age of 8 years, and the critical period of growth faltering is birth to 2 months of age.13 A study in Burkina Faso with 532 subjects also showed that children with stunting showed lower neuropsychological scores at age 6-8 years of age compared to the non-stunting children. 14
Chang's research also showed the effects of stunting by comparing groups non-stunting children in terms of fine motor skills with stunting group. Children with stunting had poor scores on test of rapid sequential continuous hand movements than the group of non-stunting children. Even in the group children with stunting had received nutritional intervention, stimulation or both, test results still showed lower scores than the group of non-stunting children. The conclusion of this study is that children with lower fine motor scores risk having lower IQs and poor school performance. 15
Longitudinal studies with 1674 children studied the effects of early stunting (ages 6-18 months) and concurrent stunting (ages 4.5-6 years) on cognitive abilities. It showed that the cognitive abilities of school-age students are associated with early stunting, but a stronger correlation is with concurrent stunting. So, interventions to prevent growth faltering not only focus on the age of under 2 years, but also continue until the age of 5 years.16
A case-control study with 77 case group (malnutrition) and 59 control group of babies born with normal weight, then experience moderate to severe malnutrition in the first year of life and the babies were followed and IQ tests were carried out in childhood, adolescence and young adults. The case group showed lower IQ score than the control group, both in childhood, adolescents and adolescents as young adults. This study concluded that moderate to severe malnutrition during infancy is associated with significant IQ disorders in young adulthood, even when physical growth has been corrected. Episodes of malnutrition during the first year of life give a risk of significant cognitive impairment during his lifetime. 17
The reason of these can be happened is persistent epigenetic effect due to malnutrition at an early age. Malnutrition at an early age can trigger epigenetic changes that persist for decades into adulthood and correlate with cognitive impairment. Deoxyribonucleic Acid (DNA) methylation is an epigenetic mechanism that is widely studied as a molecular carrier of nutritional influences during critical windows of development, assuming there is no change in environmental conditions.18
Mechanism of stunting can interfere cognitive function is correlated with low protein diets. Children with stunting have lower levels of essential amino acids than non-stunting children. Inadequate intake of essential amino acids has a negative effect on growth, because amino acids play a role in protein formation and synthesis of mammalian Target of Rapamycin Complex 1 (mTORC1). The role of mTORC1 is mainly in bone and chondral plate growth, skeletal muscle growth and homeostasis, nerve myelination processes, small intestinal homeostasis, hematopoiesis and iron metabolism, immune function and organ development. mTORC1 is very sensitive to the availability of essential amino acids for its activation, because growth factors and energy cannot overcome the lack of essential amino acids to activate mTORC1. 19