Although there are socio-demographic diversities between different parts of the country, it seems that the stature of Iranian children has been improving over the past decades . For example, results of a study in Northern Iran suggested that prevalence of stunting has been reduced from 32.8% (95% Cl; 31.0–34.6) in 1998 to 15.7% (95% Cl;14.3–17.2) in 2013 . However, results of several studies suggested that short stature is still a major health problem in Iran [20, 21]. This study is conducted to understand the timing of stunting among boys and girls. Defining the starting point of stunting is a critical step in the detection and prevention of growth retardation.
Results of a pooled data analysis demonstrated significant benefits of exclusive breastfeeding on morbidity and mortality among children, [22, 23]. During infancy, several issues cause major concerns regarding the growth of a child. These include genetic deformities, environmental hazards and nutritional factors . The recruited infants in the current population-based cohort study were all apparently healthy with normal anthropometric indexes at birth. This was done to minimize the effects of genetic factors and factors related to the antenatal period. Results from the first phase of our study revealed a number of factors altering the chance of stunting among the study population. Accordingly, diet (i.e. consumption of animal protein and dairy products and duration of breastfeeding) and socio-economic factors (i.e. family income and mother’s occupation) were reported to be effective in linear growth . The current study aimed to define the age of the participants at which the retardation (stunting) starts. Also, to make a distinction between the patterns of growth among stunted and normal children in each gender, three important anthropometric measures from birth to the age of 7 (12 measures for height and weight and 6 measures for head circumference) were included in the analysis. The results revealed a very important phenomenon in the linear growth of the stunted children, i.e. stunted boys and girls, experienced a significant diversion from the linear growth of the normal children (and the corresponding standard growth chart) at about 6 months and 9 months of age respectively. However, as presented in the results section, the time of shifting in growth seems similar in boys and girls, as on average, the stunted girls were taller than normal children from birth to 6th month of age. At this age, the stunted children started to become shorter than the normal children. At about six months of age, children start experiencing important changes such as, start weaning from breast milk and start eating supplementary and more solid foods.
According to the present study, the estimated prevalence of stunting among the study population was about 18%. The prevalence of stunting in Iranian children and its associated factors have been addressed in several studies [18, 25,26,27], However, these studies did not pay any attention to the temporal pattern of stunting and the approximate age of stunting among the Iranian children. For example, a systematic review and meta-analysis on the prevalence of stunting in Iranian children under 5-years of age estimated that the pooled prevalence of stunting is 12% (95%CI: 10–14) and that the prevalence of stunting in boys (10%) and girls (9%) are equal . The review also suggested that the overall prevalence of stunting in Southern provinces (including Fars) of Iran is mostly higher (17%) than in western (9%), eastern (8%), southern (17%) and central regions (15%) . However, this review did not examine the reasons for these discrepancies and the age at which the faltering of linear growth is started.
Results of a study on the prevalence of stunting in 3147 school children from 5 districts of Tehran suggested that only 4% of the study participants were defined as stunted. The authors concluded that birth weight, maternal age and fathers’ height are the major contributing factors in stunting among the study population. However, the study provided no stratification analysis by sex and timing of growth retardation . Emamian et. al., suggested a considerable socio-economic inequality in stunting among the Iranian population and that maternal education was the most important factor associated with stunting among children under 6 years . Again, no timing for stunting was reported.
A study in rural Guatemalan children shows that growth faltering starts soon after birth. Authors suggested that at 3 year of age, growth-retarded children were on average 3.6 kg lighter than the WHO/CDC growth chart. Also, between 19% and 34% of the deficit at 3 years of age was due to failure to thrive during the first 3 months of life, 12% to 19% between 3 and 6 months and 12% to 25% between 6 and 9 months of age . However, the authors did not report the status of the linear growth of the study population.
Results of a population-based cohort study in sub-Saharan Africa provided evidence that retardation of linear growth among children under 5 years of age started soon after birth and continued throughout infancy . The authors suggested that among several factors considered in the study (including; complementary feeding, morbidity, maternal short stature and gender) the strongest predictor of severe stunting at 12 months of age was small birth size . Another cohort study has suggested that retardation in linear growth among Zambian infants is more sever at about 13 months of age. According to the authors, the suggested age is about the time which nearly all the infants have weaned off breast milk a factor which may have severely affect children’s growth .
The results of the current study also revealed another age at which growth rate becomes smaller among stunted children and even more diversion from normal growth is observed (about 24 months of age). At this age, children start walking, touching objects, go outside home and more importantly eat family foods. Interestingly, the reduced growth rate continues for girls to the end of the follow-up period but for boys, another major reduction occurs at the fourth year of age. At this age, boys start more active playing with friends or other siblings, whereas girls do sedentary plays . That is why, as presented in the figures, weight for age among girls of both stunted and normal groups is higher than the corresponding standard weight for age of the same gender.
Strength and limitations
The participants in the present study were selected randomly among all children in the defined population. Participant’s growth indexes were followed from birth until 7 years of age. All children had normal height and weight at birth helping us to control for genetic and antenatal related factors affecting growth. All information regarding the growth and diet of the participants was collected from the participant’s health file. Also, Therefore, major sources of recall or reporting bias are not expected to exist. However, as some information collected from the phone interview, this may prone to recall and information bias, that may affect the results. To tackle this recall and reporting biases, mothers were not told why they were selected (whether if their child is a case or control). Additionally, no detailed information was available for the supplementary foods and adequacy of breast milk. Lastly, as the main aim of this study was to find approximate age at which stunting starts among boys and girls, we did not examined the prevalence of severe, moderate and mild stunting in both genders, which we recommend to be examined in the further research on stunting.