Genetic Factors Play a Significant Role in Adult Insomnia, Twin Study Finds

Summary: A large longitudinal twin study indicates that genetic influences substantially contribute to insomnia symptoms in adults and that these genetic effects are stronger in women than in men. While genetics account for a meaningful portion of insomnia risk, individual environmental factors remain important contributors.

Key Findings

Researchers analyzing data from the Virginia Adult Twin Studies of Psychiatric and Substance Use Disorders found that the heritability of insomnia symptoms differs by sex. In a longitudinal model that accounts for measurement error, the estimated heritability for the underlying insomnia trait was about 59% in females and 38% in males. These results suggest that genetic factors are largely stable over time and have a stronger influence on insomnia symptoms in women than in men.

Study Design and Methods

The research team, led by Mackenzie Lind (doctoral candidate) and senior author Ananda B. Amstadter, PhD, used data from approximately 7,500 participants in the Virginia Adult Twin Studies. Insomnia symptoms were assessed with a shortened version of the Symptom Checklist-90 at two non-overlapping time points. A composite score combined three insomnia-related items: trouble falling asleep, restless or disturbed sleep, and early morning awakenings.

Using twin modeling implemented in OpenMx, the investigators decomposed variance in insomnia symptoms into genetic and environmental components, evaluated the stability of those influences over time, and tested for sex differences. The longitudinal measurement model adjusted for measurement error, providing estimates for a latent insomnia factor rather than relying solely on raw symptom scores.

Detailed Results

Univariate models showed modest heritability for insomnia symptoms at each time point (around 22–25%). However, once measurement error was accounted for in the longitudinal latent-factor model, heritability estimates rose substantially and revealed quantitative sex differences. The latent insomnia factor demonstrated approximately 59% heritability in females and about 38% heritability in males.

Despite the notable genetic contribution—especially among women—unique environmental influences continued to explain a large portion of variance in insomnia symptoms. This indicates that nonshared experiences, lifestyle, health status, stress, and other individual-level environmental factors remain critical targets for prevention and intervention.

Clinical and Public Health Context

According to the American Academy of Sleep Medicine, transient insomnia symptoms affect roughly 30–35% of the population, while chronic insomnia (defined as symptoms at least three times per week for at least three months) affects approximately 10% of adults. Insomnia disproportionately affects women, and this study provides some of the first formal longitudinal evidence indicating stronger genetic influences on insomnia liability in adult females compared with males.

Implications

These findings have several practical implications: they highlight the importance of considering sex differences in insomnia research and suggest that genetic risk may explain a larger share of symptom development in women. At the same time, the persistent role of unique environmental factors underscores the continued relevance of behavioral, psychological, and environmental interventions for those experiencing insomnia symptoms. Clinicians and researchers may consider prioritizing targeted sleep interventions for women while continuing to address modifiable environmental contributors in all patients.

Funding: Supported by grants from the National Institutes of Health (NIH).

Source: American Academy of Sleep Medicine (press summary prepared by Lynn Celmer).

Original Research: Lind MJ, Aggen SH, Kirkpatrick RM, Kendler KS, Amstadter AB. A Longitudinal Twin Study of Insomnia Symptoms in Adults. Sleep. Published online August 11, 2015. doi:10.5665/sleep.4982

Conclusion

This longitudinal twin study reinforces the role of genetic influences in adult insomnia and provides new evidence for sex-specific genetic effects. While genetics appear to play a larger role for women, substantial environmental contributions mean that treatment and prevention strategies addressing behavioral and situational factors remain essential for reducing insomnia symptoms across the population.