Our modern lifestyles are in conflict with our internal timekeepers. Since the invention of the lightbulb over a century ago, the mass majority of us no longer wake with the sunrise or crawl into bed right after sunset - but our bodies still move by this rhythm. We all have a 24-hour clock inside of us that jumps into action the day we’re born, and continues ticking daily for the rest of our lives. However, there is another lesser known timekeeper experienced by individuals with a female physiology, which follows a monthly rhythm and is also often negatively affected by our modern lifestyles. Both of these internal clocks are deeply interwoven with our sleep needs, but did you know that these needs vary from individual to individual? And even more interestingly, women might actually need more sleep than men…
The circadian rhythm, controlled by a group of 20,000 nerve cells in the brain, is a 24-hour cycle that regulates our daily bodily processes, from body temperature to digestion to sleep (WebMD, 2022). It also reigns over the production of certain hormones, especially cortisol (which boosts alertness in the morning) and melatonin (which makes you sleepy at night) (Alisa Vitti, In the Flo).
The biggest influence on the circadian rhythm is light; your body’s sleep schedule is naturally connected to the sun - it knows to sleep when it’s dark and wake when it’s light. The circadian rhythm can be thrown off by many factors, like medications, phone screens or stress, and a disrupted circadian rhythm can affect everything from memory to cardiovascular health to skin (Healthline, 2022). Thankfully, there are many ways to reset your circadian rhythm. Spending time outdoors in natural light, sticking to a routine sleep schedule, avoiding caffeine in the evenings and powering off screens at least an hour before bedtime can all help to get you back on track.
All humans experience the innate clock of the 24-hour circadian rhythm, but did you know that individuals with female physiology actually experience another rhythm as well? This other rhythm is a 28-day cycle that regulates the menstrual cycle, known as the infradian rhythm (Alisa Vitti, 2021). The infradian rhythm influences many bodily functions, from metabolism to stress response to the microbiome. This rhythm cycles on a monthly basis, whereas the circadian rhythm cycles on a daily basis, and the two combined plays a big part in women’s sleep needs.
If you have female physiology, your sleep needs fluctuate throughout the month, in flow with your infradian rhythm. Since women follow a 28-day cycle, stress management will also look different for women than it will for men. Without tools for stress management, women can suffer from chronically high cortisol levels, which decreases progesterone levels and leads to poor sleep. In her book In the Flo, Alisa Vitti explains that when hormones are in balance, production of progesterone kicks in around ovulation (around day 14 of the average menstrual cycle), which promotes relaxation and improves sleep.
Progesterone production during ovulation is important to improve sleep, to balance out the sleep challenges that may come as hormones fluctuate. Progesterone then drops a few days before the menstrual phase (day 25-28 of the average cycle). Circadian rhythms are also more stunted during this phase - which is due largely to the fact that melatonin levels and basal temperature don’t fluctuate daily during this phase, according to behavioral sleep scientist Jade Wu, Ph.D. Basal temperature indicates that the body is fully at rest, and melatonin is a naturally produced hormone that makes you sleepy, so sleep tends to be a little worse during this phase.
According to Alisa Vitti, people with female biochemistry need more sleep than those with male biochemistry because they have a more complex brain (including a larger prefrontal cortex and hippocampus), which needs 20 minutes longer to clean itself and reset for the cognitive day (Stanford Medicine, 2017). Women’s brains are literally wired to need more sleep than men to not only thrive, but to properly function. However, a survey conducted by the American Sleep Association and Women’s Health revealed that 88% of women don’t sleep through the night on a regular basis, and one third say they never get a solid, uninterrupted night of sleep. “Women are also twice as likely as men to have chronic fatigue syndrome,” says Alisa Vitti in her book In the Flo.
It impacts everything from mood to digestive health to fertility. And it doesn’t help that culturally, women are more likely to sacrifice quality sleep than men. Sleep specialist Marc Leavey, M.D., says, “I see women dismiss their sleep needs over and over [to cater to their partner’s sleep preferences] to keep peace in the bedroom.”
According to the Family Caregiver Alliance, women disproportionately serve as informal caregivers, which often goes hand in hand with experiencing heightened stress and more sleep interruptions. Additionally, a 2018 study shows that gender norm based division of household obligations, including childcare, places additional strain on women, which affects their sleep patterns.
Restorative sleep doesn't need to be an unattainable fairytale that we only dream of. As we understand more and more how much sleep impacts every aspect of our lives, we must shift our cultural narrative from the relentless pursuit of productivity to the relentless pursuit of high quality rest. Gaining a deeper understanding of our circadian and infradian rhythms empowers us to connect with and embody them. When we learn how to sync to our innate cycles, our sleep improves. And when our sleep improves, so does our quality of life.
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