Table 4.
Association of length of only-child period and overweight at age 8 among boys, using logistic regression (n = 7,576).
| Crude | Model 1 b | Model 2 c | |||||
|---|---|---|---|---|---|---|---|
| Odds ratio | 95% CI | Odds ratio | 95% CI | Odds ratio | 95% CI | ||
| Length of only child period | Only children (n = 2,247) | Ref | Ref | Ref | Ref | Ref | Ref |
| Age gap shorter than 1.5 years (n = 367) | 0.90 | (0.69, 1.19) | 0.93 | (0.70, 1.23) | 0.89 | (0.67, 1.20) | |
| Age gap 1.5 years to shorter than 4 years (n = 4,115) | 0.76 | (0.67, 0.86) | 0.82 | (0.71, 0.94) | 0.83 | (0.72, 0.96) | |
| Age gap 4–8 years (n = 847) | 0.70 | (0.57, 0.87) | 0.75 | (0.61, 0.93) | 0.78 | (0.62, 0.97) | |
| Household income at age 0.5a | – | – | 0.99 | (0.96, 1.02) | 0.99 | (0.96, 1.02) | |
| Birth weighta | – | – | 1.06 | (1.04, 1.07) | 1.12 | (1.10, 1.14) | |
| Mother's age at birtha | – | – | 1.19 | (1.02, 1.38) | 1.19 | (1.02, 1.39) | |
| Mother's education level | Junior high school | – | – | Ref | Ref | Ref | Ref |
| High school | – | – | 0.74 | (0.52, 1.04) | 0.71 | (0.50, 1.01) | |
| Vocational school | – | – | 0.69 | (0.49, 0.97) | 0.70 | (0.49, 0.998) | |
| Higher education | – | – | 0.58 | (0.40, 0.84) | 0.59 | (0.40, 0.86) | |
| Others | – | – | 1.26 | (0.32, 5.01) | 2.07 | (0.51, 8.36) | |
| Missing | – | – | 0.90 | (0.53, 1.53) | 0.84 | (0.48, 1.50) | |
| Mother's smoking status at age 0.5 | No | – | – | Ref | Ref | Ref | Ref |
| Yes | – | – | 1.41 | (1.19, 1.67) | 1.36 | (1.14, 1.63) | |
| Missing | – | – | 1.87 | (0.85, 4.14) | 1.79 | (0.78, 4.09) | |
| Father residence at age 0.5 | Yes | – | – | Ref | Ref | Ref | Ref |
| No | – | – | 1.28 | (0.89, 1.86) | 1.18 | (0.80, 1.72) | |
| Preterm birth | No | – | – | – | – | Ref | Ref |
| Yes | – | – | – | – | 1.38 | (1.00, 1.89) | |
| Duration of breastfeeding | None | – | – | – | – | Ref | Ref |
| 1–2 months | – | – | – | – | 1.02 | (0.77, 1.35) | |
| 3–5 months | – | – | – | – | 0.89 | (0.67, 1.18) | |
| 6 or more months | – | – | – | – | 1.05 | (0.81, 1.36) | |
| Missing | – | – | – | – | 1.16 | (0.64, 2.08) | |
| Rapid growth during early childhoodd | No | – | – | – | – | Ref | Ref |
| Yes | – | – | – | – | 3.07 | (2.67, 3.52) | |
| Missing | – | – | – | – | 1.79 | (1.40, 2.29) | |
| Exercise habit at age 8 | Yes | – | – | – | – | Ref | Ref |
| No | – | – | – | – | 1.12 | (0.99, 1.27) | |
| Breakfast consumption at age 8 | Yes | – | – | – | – | Ref | Ref |
| No | – | – | – | – | 1.30 | (0.94, 1.80) | |
| Missing | – | – | – | – | 0.93 | (0.58, 1.49) | |
| Excessive screen time at age 8e | No | – | – | – | – | Ref | Ref |
| Yes | – | – | – | – | 1.24 | (1.08, 1.42) | |
| Missing | – | – | – | – | 1.00 | (0.21, 4.85) | |
| Irregular sleeping hours at age 8 | No | – | – | – | – | Ref | Ref |
| Yes | – | – | – | – | 0.90 | (0.60, 1.34) | |
| Missing | – | – | – | – | 0.84 | (0.18, 3.99) | |
| Healthy dinner habits at age 8f | Yes | – | – | – | – | Ref | Ref |
| No | – | – | – | – | 1.06 | (0.93, 1.21) | |
| Missing | – | – | – | – | 0.32 | (0.04, 2.56) | |
| Grandparent cohabitation at age 8 | No | – | – | – | – | Ref | Ref |
| Yes | – | – | – | – | 1.23 | (1.07, 1.41) | |
CI; confidence interval.
Bolded values indicate statistical significance at p <0.05.
Mother's age at birth, birth weight and household income at age 0.5 were scaled so that the effect of a one-unit change can be interpreted as the effect of a 10-year change in age, 100-g change in weight, and one million JPY change in income, respectively.
Model 1 adjusted for household income at age 0.5, birth weight, mother's age at birth, mother's education level, mother's smoking at age 0.5, and father cohabitation at age 0.5.
Model 2 adjusted for preterm birth, duration of breastfeeding, rapid growth during early childhood, exercise habit at age 8, breakfast consumption at age 8, excessive screen time at age 8, irregular bedtime at age 8, healthy dinner habits at age 8, and grandparent residence at age 8 in addition to covariates adjusted in Model 1.
Rapid growth during infancy was determined as gaining more than 0.67 SD of weight from age 0.5 years to age 1.5 years (32).
Excessive screen time was determined as 2 or more h of watching TV or playing computer games on either weekdays or weekends at the age of 8 years old (33).
Unhealthy dinner habits were determined by frequent or occasional consumption of instant food and precooked food, using food delivery, or eating out on weekdays, which was asked at the age of 8 years old.