New study links number of children to dementia risk

Compared to individuals with two or three children, those with no children or just one child had a 30% higher risk of dementia, while those with four or more children had a 12% increased risk. The study analyzed data from nearly 10,000 participants in the HUNT Study in Norway.

“Our research suggests that the number of children a person has may be linked to their risk of developing dementia later in life,” says lead author and postdocTeferi Mekonnen from the Norwegian Institute of Public Health. 

However, the authors emphasize that this is an observational study and that they did not identify factors explaining the mechanisms behind the observed relationship between the number of children and dementia later in life.

Key findings 

• Among the 9,745 participants in the study, 15.7% were diagnosed with dementia.
• The proportion of participants with dementia was 22.3% among those with no children, 21.4% among those with one child and 19.9% for those with four or more children.
• Those with two and three children had the lowest risk of dementia, with 12.6% and 13.4% diagnosed cases of dementia, respectively.
• Compared to participants with 2-3 children, those with no children or one child had a 30 % higher risk, and those with four or more children had a 12% higher risk of dementia at age 70. 
• Surprisingly, the authors found that neither psychosocial factors, socioeconomic characteristics, chronic disease nor lifestyle factors seemed to explain the higher dementia risk associated with having fewer or more children.

Potential mechanisms

Previous studies have shown a similar relationship between the number of children and increased dementia risk.  This study is the first to explore the potential factors mediating this relationship.  The researchers checked whether numerous mediating factors explained the effect of the number of children on dementia risk, including psychosocial factors, occupational complexity, chronic disease nor lifestyle factors but they found that none of these factors seemed to mediate the total effect on dementia risk among those who had 0, 1 or more than 4 children. 

“The absence of mediating effects in our study may either be due to poor data quality, measurement errors, or due to unmeasured and complex multifactorial mediators such as quality of life, diet, the amount and quality of sleep, and various forms of social support, which potentially vary by the number of children,” says Mekonnen.

Neuroprotective effects of having children 

Having two to three children was found to have the lowest risk of dementia and this may be due to several potential protective mechanisms, which were not directly accounted for in the study. 

“Social engagement and support from children can help maintain cognitive function, as social interaction has been associated with better mental health and a lower risk of dementia,” says Mekonnen.

“Furthermore, having children may also foster a sense of purpose and emotional well-being, which are linked to better cognitive health. Additionally, raising children involves cognitive and emotional stimulation, which can keep the brain active and contribute to cognitive reserve,” says Mekonnen. 

Childless individuals may have smaller networks and engage in unfavourable lifestyle behaviours, and thus be at higher risk of chronic diseases.

Having four or more children was, however, associated with an increased risk of dementia, and it has previously been speculated that this may be due to socioeconomic factors and stress, but the researchers found no such associations in their data.

About this study

Everyone over the age of 70 with a registered address in Nord-Trøndelag in 2017 was invited to participate in the study. Among the 19,463 invited, 9,745 individuals took part in the cognitive tests (50% participation). The participants took cognitive tests as part of the HUNT4 70+ sub-study between 2017 and 2019, when their average age was 78 years.

The researchers linked registry data from earlier surveys conducted in 1984-86 and 1995-97. They used causal mediation analysis to explore mediating pathways, including socioeconomic position (with occupational complexity as a proxy for cognitively stimulating environments), psychosocial factors (such as participation in social activity, loneliness, life satisfaction), lifestyle factors (including smoking, physical inactivity, alcohol intake), and markers of chronic diseases (obesity, diabetes, depression score, hearing impairment, and hypertension). The analyses were adjusted for other relevant factors, such as the participants’ age, sex, marital status at age 25, level of education, and religion. 

Although this study has several strengths, including a large, population-based sample and high-quality registry data on the number of children, there are some limitations, the main being a healthy selection bias in the study sample as the participants were most likely healthier than the general population. The indirect effect estimates for the factors such as lifestyle behaviors and chronic diseases might be underestimated, if there is competing risk. In addition, the study did not consider genetics. 

Reference

The study is published in the journal BMC Neurology: Number of children and dementia risk: a causal mediation analysis using data from the HUNT study linked with national registries in Norway. BMC Neurology volume 25, Article number: 39 (2025). Published online 27 January 2025.