Key Finding: Parent-child BMI associations after birth may primarily be due to genetic inheritance, suggesting that reducing parental BMI alone may not cause large reductions in childhood obesity risk.
A Major Study Investigates Genetic Confounding
A new study using data from the Norwegian Mother, Father and Child Cohort Study (MoBa) has examined whether the well-known links between a parent’s body mass index (BMI) and their child’s weight are actually caused by shared genetics, rather than the family environment.
The analysis included up to 85,866 children (51.3% male) in linear regression models and up to 50,999 children in structural equation models (SEM). Researchers looked at maternal pre-pregnancy BMI and paternal BMI during pregnancy as the primary exposures, comparing their associations with a wide range of offspring outcomes.
Key Outcomes Measured
The study tracked children from birth through age 8, examining:
- Birth weight
- BMI at 6 months, 1, 2, 3, 5, and 8 years
- Appetite-related eating behaviors at age 8
Critical Findings on Parent-Child BMI
For birth weight, the story was different than for later childhood. Maternal BMI showed a stronger association with offspring birth weight than paternal BMI, suggesting a direct, prenatal environmental effect during pregnancy.
However, from 6 months onward, the pattern shifted dramatically. For childhood BMI, the associations for mothers and fathers were very similar. This symmetry is a classic signature of genetic inheritance, as children share roughly half their genes with each parent but are only exposed to one mother’s womb.
The formal statistical models (SEM) confirmed this shift:
- For 8-year BMI: Genetic confounding accounted for 79% (95% CI: 62%–95%) of the association for maternal BMI and 94% (95% CI: 72%–113%) for paternal BMI.
- For birth weight: Genetic confounding did not explain the association, reinforcing the idea of a direct intrauterine effect.
Impact on Eating Behaviors
The study also found that higher parental BMI was significantly associated with offspring food responsiveness and emotional overeating at age 8, further supporting a genetic link to appetite regulation.
Limitations to Consider
The authors note several important limitations of the study:
- Selective recruitment and attrition within the MoBa cohort.
- Potential bias from parental assortative mating (the tendency for people with similar BMIs to partner).
- Limited generalizability, as findings may not apply to low-income countries or settings with very different obesity prevalence.