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Evaluating the seasonality of growth in infants using a mobile phone application
Satoshi Narumi1, Tetsu Ohnuma2, Kenji Takehara3
1Department of Molecular Endocrinology, National Research Institute for Child Health and Development, Tokyo, 157-8535 Japan.
Insights
Infant linear growth velocity shows seasonal variation, increasing in summer and decreasing in winter. This seasonal effect on infant growth was observed in Japanese infants, unlike weight gain.
Area of Science:
- Pediatrics
- Human Growth and Development
- Environmental Health
Background:
- Seasonal variations in growth velocity are documented in toddlers and school-aged children.
- Such seasonal patterns in growth have not been previously established in infants.
Purpose of the Study:
- To investigate seasonal differences in infant growth velocity, specifically for length and weight.
- To determine if infant growth patterns exhibit seasonality.
Main Methods:
- Longitudinal growth data (length and weight) from 9,409 Japanese infants (2014-2017) were analyzed.
- Growth velocity was calculated as the mean daily change in sex- and age-adjusted z-scores (ΔLAZ/day and ΔWAZ/day).
- Multilevel linear regression adjusted for age, sex, nutrition, and birth season.
Main Results:
- Linear growth velocity (ΔLAZ/day) demonstrated significant seasonal variation, with increases observed during summer.
- A statistically significant difference in ΔLAZ/day was found between winter and summer (mean difference 0.0026, P < 0.001).
- Nutrition showed a modest effect on linear growth, with differences between formula-fed and breastfed infants.
Conclusions:
- Japanese infants exhibit significant seasonality in linear growth, characterized by accelerated growth in summer and reduced growth in winter.
- Weight gain in infants did not show significant seasonal variation in this study.
- These findings highlight the influence of environmental factors, such as season, on early human development.
Abstract:
It has been observed that growth velocity of toddlers and school children shows seasonal variation, while such seasonality is unknown in infants. The aim of this study was to examine whether growth velocity (length and weight) of infants differs by seasons. We assessed longitudinal measurement data obtained for 9,409 Japanese infants whose parents used the mobile phone application, "Papatto Ikuji", during the period from January 2014 to October 2017. On average, each infant had 4.8 entries for length and 5.4 entries for weight. The mean daily change in sex- and age-adjusted z-scores between two time points was estimated as the growth velocity during that period: ΔLAZ/day and ΔWAZ/day for length and weight, respectively. We analyzed 20,007 ΔLAZ/day (mean, -0.0022) and 33,236 ΔWAZ/day (mean, 0.0005) measurements, and found that ΔLAZ/day showed seasonal differences with increases during summer. We conducted a multilevel linear regression analysis, in which effects of age, sex, nutrition and season of birth were adjusted, showing significant difference in ΔLAZ/day between winter and summer with a mean ΔLAZ/day difference of 0.0026 (95%CI 0.0015 to 0.0036; P < 0.001). This seasonal difference corresponded to 13% of the average linear growth velocity in 6-month-old infants. A modest effect of nutrition on linear growth was observed with a mean ΔLAZ/day difference of 0.0015 (95%CI 0.0006 to 0.0025; P < 0.001) between predominantly formula-fed infants and breastfed infants. In conclusion, we observed that linear growth, but not weight gain, of Japanese infants showed significant seasonality effects represented by increases in summer and decreases in winter.
