The long-term health effects of initiating smoking in adolescence: Evidence from a national longitudinal survey

Impact of BMI and smoking in adolescence and at the start of pregnancy on birth weight

BACKGROUND

Birth weight is an indicator of intra-uterine conditions but also a determinant for future health. The importance of preconception health for a healthy birth weight has been emphasized, but evidence is lacking on how modifiable factors in adolescence, such as body mass index (BMI) and smoking, affect future pregnancy outcome. We evaluated associations between BMI and smoking in adolescence and at the start of pregnancy and birth weight of the first-born child.

METHODS

This longitudinal study included 1256 mothers, born 1962-1992, and their first-born children, born between 1982-2016. Self-reported questionnaire information on weight, height and smoking at age 19 was cross-linked with national register data obtained at the start of pregnancy and with the birth weights of the children. Univariable and multivariable linear regressions were performed to determine the impact of maternal factors at 19 years of age and at the start of the pregnancy respectively, and the importance of BMI status at these points of time for the birth weight of the first child.

RESULTS

BMI and smoking at the start of the pregnancy displayed strong associations with birth weight in a multivariable analysis, BMI with a positive association of 14.9 g per BMI unit (95% CI 6.0; 23.8 p = 0.001) and smoking with a negative association of 180.5 g (95% CI -275.7; -85.4) p = 0.0002). Smoking and BMI at 19 years of age did not show this association. Maternal birth weight showed significant associations in models at both time-points. Becoming overweight between age 19 and the start of the pregnancy was associated with a significantly higher birth weight (144.6 (95% CI 70.7;218.5) p = 0.0002) compared to mothers with normal weight at both time points.

CONCLUSIONS

Our findings indicate that the time period between adolescence and first pregnancy could be a window of opportunity for targeted health promotion to prevent intergenerational transmission of obesity.

Proportion and trend in the age of cigarette smoking initiation among adolescent smoking experiencers aged 13-15 years in 148 countries/territories

Background

Limited studies have assessed the recent proportion and trend in the age of cigarette smoking initiation among adolescent smoking experiencers globally. We aimed to assess the recent global proportion, associated factors and the long-term trend of the initiated age of cigarette smoking among adolescent smoking experiencers.

Methods

We used data from the most recent Global Youth Tobacco Survey on 99,728 adolescent smoking experiencers aged 13-15 years from 144 countries/territories (hereafter "countries") that had conducted at least one survey in 2010-20, to assess the recent proportion of the age of cigarette smoking initiation. Additionally, we used data from 148 countries that had conducted ≥2 surveys between 1999 and 2020, to assess the trend in the average age of cigarette smoking initiation.

Results

Among 99,728 adolescent smoking experiencers aged 13-15 years, the proportions of initiating cigarette smoking when aged ≤ 9 years, 10-11 years, 12-13 years, and 14-15 years were 22.8% (95%CI 21.3-24.4), 18.8% (17.3-20.2), 36.8% (34.5-39.2), and 21.6% (19.9-23.2), respectively. The average age of cigarette smoking initiation decreased by 0.44 years per 5 calendar-years averagely in 17 (11.5%) of 148 countries, was unchanged in 95 (64.2%) countries, and increased by 0.38 years per 5 calendar-years averagely in 36 (24.3%) countries. Higher income category (reference group: low-income countries; lower-middle-income: OR = 0.44, 95%CI = 0.28-0.70; upper-middle-income: OR = 0.56, 95%CI = 0.38-0.83; high-income: OR = 0.35, 95%CI = 0.22-0.53) and Framework Convention on Tobacco Control ratification (OR = 0.51, 95%CI = 0.42-0.63) were inversely associated with early cigarette smoking initiation.

Conclusions

A substantial proportion (~80%) of adolescent smoking experiencers aged 13-15 years initiated cigarette smoking before 13 years, and the average age of cigarette smoking initiation decreased or remained unchanged in nearly three quarters of the countries surveyed. These findings emphasize that national governments around the world need to strengthen intervention strategies and measures aimed at children and adolescents to prevent smoking up-take.