It has partly to do with women’s genetic make-up, researchers claim in a paper published this month in the journal Sleep. A team of geneticists conducted a longitudinal analysis of data from a large twin study and found that the estimated heritability of insomnia was 38 percent for males and 59 percent for females.
Beyond this, the factors that make women more vulnerable to insomnia are not so clear. One line of thinking is that women’s increased risk may have to do with hormonal changes associated with the reproductive system. Here are some recent findings about women’s susceptibility to insomnia during the reproductive years.
It Starts Early
The pattern of insomnia showing up in more females than males starts to emerge in high school-age teens, according to epidemiological research. This could be partly attributable to cyclic changes that occur with menstruation and menstrual cycle disorders. The hormones that regulate reproductive functions also affect sleep.
Women report the greatest number of premenstrual symptoms (e.g., headaches, bloating, and mood swings) in the days leading up to menstruation, when estrogen and progesterone levels are falling.
In 3 to 8 percent of women, these premenstrual symptoms are severe, say the authors of a review paper on sleep and women’s health. Women with premenstrual syndrome (PMS) or premenstrual dysphoric disorder (PMDD) typically report disturbed sleep in the week leading up to, and the first few days of, menstruation: insomnia, frequent awakenings, and non-restorative sleep. Women with PMS and PMDD also report sleepiness, fatigue, mood swings, and trouble concentrating. The hormonal fluctuations behind these symptoms, which resolve with the onset of menstruation or soon thereafter, may be a factor in women’s increased vulnerability to insomnia.
Tests have not turned up much evidence of these subjective complaints. (So there’s a need for more fine-grained tests.) But in one study, older women of reproductive age were found to sleep less efficiently in the week leading up to menstruation. Researchers also found that women who experienced a steeper rise in progesterone in the middle of the menstrual cycle tended to experience more wake time and sleep fragmentation in the days approaching menstruation.
Insomnia During Pregnancy
Changes that occur during pregnancy also cause an increase in sleep problems. Hormonal fluctuations are involved, as well as anatomic and physiologic changes that give rise to symptoms such as backache, breast tenderness, fetal movement, and urinary frequency, which may interfere with sleep. Pregnant women who experience more wake-ups and poor sleep quality typically report that the sleep problems worsen as their pregnancies progress.
By the third trimester, women are waking up 3 to 5 times a night. The prevalence of insomnia is about 21 percent. (Compare this to the 10 percent of the general population said to have insomnia.) Sleep studies have shown that pregnant women get less sleep in the third trimester and that their sleep is lighter and more fragmented.
Persistent Sleep Problems
Disrupted sleep is common among women (and men) with infants. But there’s not much information about if and when the sleep problems connected with pregnancy and childbirth resolve.
Norwegian researchers recently looked into these questions. They analyzed data from a longitudinal study of 1,480 healthy women to ascertain the prevalence of insomnia during 3 time periods. Using well-validated scales, they found the prevalence of insomnia to be quite high both during and after pregnancy:
- week 32 of pregnancy—60 percent reporting insomnia
- week 8 postpartum—60 percent reporting insomnia
- year 2 postpartum—41 percent reporting insomnia
A notable aspect of this study is not just the high percentage of women reporting insomnia but also how persistent the insomnia symptoms were. By year 2 postpartum, the prevalence of insomnia was still quite high compared with the prevalence of insomnia in the general population (and concurrent maternal depression could not explain this persistence). The researchers suggested that pregnancy-related sleep problems may become chronic, and that this might contribute to explaining why insomnia is more common in middle-aged and older women than in men in the same age groups.
We’ll explore the increased risk of insomnia in middle-aged and older women in Part II sometime next month.