“Not getting restorative sleep may do more than just affect our functioning the next day; it might also influence the rate at which our biological clock ticks,” said first author Judith Carroll, adding: “In the women we studied, those reporting symptoms such as restless sleep, waking repeatedly at night, having difficulty falling asleep, and waking too early in the morning tended to be older biologically than women of similar chronological age who reported no symptoms.” For their findings, both studies used a “biological clock” developed by Horvath, which has become a widely used method for tracking the epigenetic shift in the genome. Epigenetics is the study of changes to DNA packaging that influence which genes are expressed but don’t affect the DNA sequence itself.

In the menopause study, Horvath and first author Morgan Levine tracked methylation, a chemical biomarker linked to aging, to analyze DNA samples from more than 3,100 women enrolled in four large studies, including the Women’s Health Initiative (WHI) a major 15-year research program that addressed the most common causes of death, disability and poor quality of life in postmenopausal women.They measured the biological age of cells from blood, saliva and inside the cheek, to explore the relationship between each woman’s chronological age and her body’s biological age.

“We discovered that menopause speeds up cellular aging by an average of 6 percent,” said Horvath. “That doesn’t sound like much but it adds up over a woman’s lifespan.”In the sleep study, Carroll and her colleagues drew their data from more than 2,000 women in the WHI. Using the epigenetic clock, they found that postmenopausal women with five insomnia symptoms were nearly two years older biologically than women the same chronological age with no insomnia symptoms.

“We can’t conclude definitively from our study that the insomnia leads to the increased epigenetic age, but these are powerful findings,” said Carroll. “In the future, we will need to carry out studies of the same individuals over an extended period of time to determine cause-and-effect relationships between biological age and sleep disorders.”