If you have not already done so, please read Blog Posts 1 through 5 that describe how sleep is important and beneficial. I will post specific information for parents and children based on my book, “Healthy Sleep Habits, Happy Child.” Please do not be put off by my book’s length. This is a reference book. Read only the topic of interest to you.
Epigenetics is the study of how behaviors and environment can cause changes that affect the way genes work without altering the underlying DNA sequence. Epigenetics acts like a layer of “switches” that can turn genes “on” or “off” and is influenced by factors like diet, exercise, stress, and sleep and can have lasting impacts on health and development. Epigenetics controls which genes are expressed, which determines when and where proteins are made in the body. Unlike genetic mutations, epigenetic changes are often reversible and can change throughout your life.
In an older paper (2020) Professor Geetha discovered that, among elementary school children, 71% of children with late bedtimes were obese, compared to only 29% of children with early bedtimes.
In a 2025 paper, Professor Geetha examined two groups of 8-year-olds. She compared those who had an early bedtime (8:30pm or earlier) with those who had a later bedtime (after 8:30pm). Using a cotton swab sample of saliva, she identified 571 unique genes associated with the bedtime. “Cross-comparison with established sleep and obesity gene sets identified ten overlapping genes. These findings suggest that variations in bedtime during childhood may epigenetically modify genes regulating circadian rhythm, metabolism, neuronal connectivity, and stress response, potentially predisposing to later-life developmental, and metabolic challenges.”
I asked the author what were the average bedtime difference between the two groups of children. It was only 41 minutes!
The bottom line is that late bedtimes are a health threat because late bedtimes modify regulatory genes. Late bedtimes might cause obesity.
Blog Posts 81,232A, and 232B describes other studies showing that obesity is associated with late bedtimes but not sleep duration.
Blog Post 14 discusses the Genetic Individuality of Your Child. Late bedtimes will affect different children differently.
