The 5 habits that protect deep sleep after 40

Deep sleep, the slow-wave stage crucial for physical restoration, immune system strengthening, and memory consolidation, often becomes lighter and less stable as women age. This makes our sleep easier to disrupt and harder to sustain as we get older. 

The good news is that the habits that support deeper, more restorative sleep are well-studied, and most are fairly accessible no matter what age you are.

👉🏽 Sleep fragmentation and deep sleep loss often overlap. Here's more on sleep efficiency and the 2–4 a.m. wake-up window.

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Deep sleep is the deepest stage of non-REM sleep. In this phase, brain waves, heart rate, and breathing slow significantly, making it hard to wake up. The brain generates slow, synchronized electrical patterns called delta waves, and research suggests this is when the glymphatic system, the brain's waste-clearance network, is most active, flushing out metabolic byproducts, including proteins linked to cognitive decline. It's also when the body releases growth hormones, consolidates declarative memories, and maintains the hormonal conditions that support glucose metabolism. It usually occurs in the first half of your night.

For many women, sleep starts to feel different in their 40s, sometimes earlier, as hormonal fluctuations affect how easily they fall asleep, how well they stay asleep, and how deeply their sleep restores them. 

“It's not just hot flashes and night sweats,” says Dr. Funke Afolabi-Brown, a Penn-trained sleep medicine physician. 

In other words, things that never used to wake you up — a noise outside, a snoring partner, a slight shift in temperature — suddenly start to because you aren’t spending as much time in a stage of sleep that’s harder to wake from. And once you're awake, falling back asleep gets harder.

Estrogen and progesterone both affect deep sleep, but not in identical ways. According to Dr. Julia Edelman, MD, FACOG, MSCP, erratic estrogen levels during perimenopause are independently disruptive to sleep, and not only through physical symptoms like night sweats. 

"Estrogen has a relationship with serotonin," she says. "When estrogen fluctuates wildly, serotonin levels are also unstable, contributing to anxiety and depression — both of which are independently associated with poor sleep quality." Research confirms this link between mood, hormonal fluctuation, and worsening sleep in perimenopausal women.

Progesterone loss is another part of aging, and lower progesterone levels are associated with more relaxed airway muscles, which increase the likelihood of disordered breathing during sleep, including sleep apnea, even in women who aren't overweight.

Beyond hormones, there’s the cognitive and emotional load that midlife often brings — more responsibilities, more worry, more difficulty quieting a mind that has been running all day. Afolabi-Brown describes this as a chronically elevated arousal state, and research supports the idea that sleep disturbance is significantly more prevalent in women entering perimenopause.

So, what can we do to get a good night’s rest?

Rather than optimizing for a specific number of hours on a sleep tracker, both experts recommend reducing the things that fragment sleep and strengthen the ones that support it. Here are five methods that work according to the evidence:

Deep sleep is closely linked to a drop in core body temperature, and research consistently supports a cooler sleep environment for deeper, less fragmented sleep. 65–68°F is a widely accepted temperature range, but Afolabi-Brown says just keep your bedroom cooler than the rest of your home: "The goal is to be comfortably cool, not frigid.”

Research shows that exercise increases delta power during sleep, effectively deepening and stabilizing it. As Johns Hopkins Medicine summarizes, moderate aerobic exercise increases slow-wave sleep. Afolabi-Brown notes one caveat though: avoid vigorous exercise within two to three hours of bedtime, as it can raise core temperature and cortisol at the wrong time of night.

Waking at the same time every day is one of the most reliable anchors for sleep quality. A systematic review of 92,340 adults found that regular sleep and wake times supported better health, and a fixed wake time gives your circadian system a daily signal. Research supports it as more stabilizing than a consistent bedtime alone.

A 2024 systematic review and meta-analysis found that REM sleep disruptions begin at as few as two standard alcoholic drinks and worsen with more. It also worsens hot flashes. Afolabi-Brown recommends stopping alcohol at least three hours before bed and hydrating well if you drink.

Caffeine deserves mention here too. Edelman notes that because of its long half-life, caffeine consumed in the early afternoon can still be measurably present in the body at bedtime for many women, so it’s best to quit before noon.

For women who run all day and then expect the body to simply switch off, a transition period between the day and sleep isn't a luxury; it's a physiological shift. “ That bedtime routine represents a buffer between that very busy, crazy day and transition to sleep,” says Afolabi-Brown. Whether you journal, gently stretch, meditate, read, or something else, the habit helps shift the nervous system out of a high-alert state before sleep. 

Sleep changes with age, but the habits that support deeper, more stable sleep are well within reach. And most of them don’t require more willpower; they just need you to embrace what your body needs to truly wind down.

Most of us are living longer. But are we living better? Dr. Mary Pardee, a naturopathic physician specializing in longevity and preventative medicine, is joining us inside The Livelong Women’s Circle to talk about the difference between lifespan and healthspan, the biological drivers of aging, and the daily habits that have the biggest impact on long-term health.

📆 Today, March 18th, 9:30 PST/12:30 EST

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This conversation is part of the Livelong community series exploring the science of living longer and living better, a preview of our soon-to-launch membership program and our upcoming Livelong Women’s Health Summit.

Women’s sleep (and women’s physiology more broadly) has been understudied for decades. If you care about prevention and elevating better conversations, we’d love to have you join us as a Livelong Ambassador for the Livelong Women’s Health Summit.

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