Have you ever done everything right, tried the diets, considered the hormones, tracked your sleep, and still felt like something was fundamentally off? You are not imagining it, and you are definitely not alone. There is a piece of the midlife health puzzle that most doctors are not talking about, and it might be the most foundational one of all.
On this episode of Midlife Conversations, I sat down with Sarah Kleiner, a certified quantum biology practitioner, health detective, and one of the most thoughtful voices in the circadian rhythm and women’s health space. What she shared genuinely shifted how I think about hormone balance, and I suspect it will do the same for you.
Who Is Sarah Kleiner and Why Does Her Story Matter?
Sarah’s health journey reads like something many midlife women will recognize. In her late 30s, she was told she was entering perimenopause. Her cycles had become wildly irregular, and she was navigating all of this while parenting a special needs child and running a demanding life. Her doctors offered progesterone and not much else.
At the same time, she had been doing a carnivore diet for two years. It had originally resolved a long list of issues, including IBS, PCOS, skin problems, and painful cycles. But something had shifted. She was gaining weight without eating any sugar, and her hormones were clearly struggling. She realized that what had once been a helpful elimination tool had become a long-term stress on her body, suppressing cortisol regulation, limiting fiber for estrogen detox, and creating the exact hormonal chaos she was trying to escape.
She eventually experienced two miscarriages and two failed IVF cycles. It was during that profoundly painful chapter that she came across the work of Dr. Jack Cruz and went deep into the science of circadian biology and light. She got certified in applied quantum biology and started rebuilding her health from an entirely different angle. At 43, she successfully delivered a healthy baby. That journey is now the foundation of everything she teaches.
Circadian Rhythm and Hormones: The Connection Most Women Miss
Most of us have heard the term circadian rhythm, but Sarah explains it at a level that actually changes behavior. Every single cell and organ system in your body operates on a circadian clock. Your brain, your thyroid, your gut, your ovaries all rely on light signals from your environment to know what time of day it is and what functions to carry out.
When those light signals are strong and consistent, meaning bright natural light in the morning and genuine darkness at night, your hormones have the opportunity to stay in sync. When they are disrupted, the downstream effects ripple through everything.
Sarah shared a striking piece of research: since smartphones entered our lives in 2010, women’s menstrual cycles have measurably changed. Artificial light at night tells your brain it is still daytime, which triggers the sex steroid hormone pathway when your body should be resting, repairing, and making melatonin. That single disruption can lower progesterone, promote estrogen dominance, and set off a cascade of symptoms that feel impossible to trace back to their source.
Morning Light Is Not Optional, It Is Metabolic
One of the most practically useful things Sarah explained is what happens when you get natural light in your eyes first thing in the morning, before screens, before sunglasses, before anything else.
The suprachiasmatic nucleus in your brain is literally scanning for light quality in the morning: the right frequency, brightness (measured in lux), and color temperature (measured in Kelvin). When you look at your phone first thing, you get a Kelvin reading of around 6,000, which signals to your brain that it is already midday. Meanwhile, your lux reading is only around 200, when your body needs 500 to 10,000 to properly activate metabolism. Your brain gets a completely contradictory signal and the whole cascade of daytime functions gets scrambled.
Getting outside, even for five minutes, gives your body the full-spectrum signal it actually needs: red, infrared, scattered UV, and the brightness that activates leptin signaling, dopamine, serotonin production, and metabolic function. Sarah shared a study showing that for every hour you delay morning sunlight exposure, BMI increases by a measurable increment. The connection between light and metabolism is not a wellness trend. It is physiology.
What You Are Doing at Night Is Quietly Wrecking Your Hormones
The evening side of the equation is just as critical. Sarah recommends keeping the light level in your environment (measured in lux) at 10 or below during the three hours before bed. Why? Because the photoreceptive cells in your eyes have memory. Even after you turn the lights off, your brain can continue registering previous light levels for anywhere from one to three hours, depending on your genetics. That means your cortisol can stay elevated long after you think you have wound down.
She recommends using her app, called My Circadian, which includes a lux meter so you can actually measure your environment. If you want to watch television, wear blue-blocking glasses and measure the lux from the screen to your eye. The goal is to keep it under 10. She uses Chroma blue blockers because they allow some of the violet spectrum through, which does not disrupt circadian rhythm the way blue and green do, making the viewing experience much more pleasant.
One simple but powerful tip she shared: adding an incandescent lamp to your indoor space, even while LEDs are on, can meaningfully counteract some of the mitochondrial stress of artificial blue light. Research by Dr. Glenn Jeffrey showed a 25% vision improvement in subjects who simply added one incandescent bulb in a room otherwise lit by LEDs.
Estrogen Dominance Might Be a Light Problem
This is where Sarah’s perspective becomes especially important for women navigating perimenopause and menopause. She makes a compelling case that estrogen dominance, one of the most commonly reported issues in midlife women, can actually originate in a disrupted light environment.
When your body is flooded with artificial light at night and the sex steroid hormone pathway is continually triggered when it should be resting, and when the absence of melatonin prevents proper progesterone production, you end up with a hormonal imbalance that no amount of supplementation will fully address. You can take all the right things and still feel terrible if this foundation is not in place.
Sarah says she has worked with women who could not tolerate HRT, fixed their light environment and terrain, and then were able to gently introduce hormones with success. She has also worked with women on HRT who wanted to come off it and were able to do so by addressing these upstream factors. Her position is what she calls Switzerland when it comes to HRT: no judgment, just foundations first.
What Sarah Thinks About HRT and Detox Pathways
Sarah’s own experience with testosterone replacement became a masterclass in why genetic and detox pathway awareness matters so much before adding hormones. When she tried low-dose topical testosterone, she experienced tooth pain, insomnia, rage, and eventually tinnitus so severe she could not sleep. Her body was not processing the testosterone as expected. Working with a practitioner who ran her genetic pathways revealed that she had compromised detox pathways that were causing the testosterone to push her estrogen levels into the floor rather than aromatizing into it normally.
She now takes only progesterone from the HRT category and has rebuilt her testosterone to a healthy level naturally through stress reduction, dietary changes, boron supplementation (which can help lower SHBG and free up bound testosterone), and continuing her light and circadian practices.
Her view on the HRT-causes-cancer debate is nuanced and worth sitting with. She believes both the claim that HRT causes cancer and the claim that HRT does not cause cancer are incorrect. What actually matters is the terrain: your genetics, your detox pathways, your environment, and whether your body is processing hormones efficiently. The same intervention can be life-changing for one woman and genuinely harmful for another.
The Order of Operations Sarah Recommends
Sarah is clear that there is a sequence to optimizing health in midlife, and light comes first, always. Before gut health, before hormones, before supplements, she starts every client with their light environment. Here is why:
Your thyroid is a circadian organ. If you are blasting it with blue light at night, thyroid hormone support will be an uphill battle. Your gut is a circadian organ. Morning light triggers serotonin production in your eyes, which stimulates gut motility. Many of Sarah’s clients find that constipation resolves simply from adding consistent morning sunlight. Your appetite hormones are a circadian organ. The UV window in morning light signals leptin and triggers alpha MSH production, a peptide that helps regulate hunger. Blood sugar dysregulation and insulin resistance are also directly connected to light exposure. Research from Dr. Jeffrey’s lab has shown that blue light alone can drive insulin resistance, and that red and infrared light are the antidote.
Once light is addressed, she moves to meal timing, seasonal eating, hydration and minerals, and then targeted supplements. Hormonal support, including HRT, comes after that foundation is solidly in place.
Practical Takeaways for Midlife Women
Sarah’s recommendations are accessible and do not require perfection. Get outside within the first hour of waking, without sunglasses if the UV index is low, for at least five minutes and ideally longer. Move your red light therapy session to the morning if you use it, but understand it does not fully replace natural outdoor light because it lacks the blue spectrum your brain needs to register daytime. Keep your indoor environment dim in the evenings. Swap overhead LEDs for incandescent lamps or candles. Use blue-blocking glasses if you are watching screens. Do not try to turn off all light at 9 pm and expect your brain to immediately shift into melatonin mode. It needs a gradual wind-down.
If you are considering HRT or are already on it, get informed about your detox pathways and genetic tendencies before adding or increasing hormones. Work with a practitioner who understands this layer of personalization.
And if you are someone who has chosen not to do HRT, for any reason, know that rebuilding circadian rhythm integrity, eating seasonally, and reducing light stress can take you remarkably far. Sarah has a coach who went into surgical menopause at 29, chose not to do HRT after a terrible initial experience, and is now, at 46, lean, healthy, and sleeping better than most teenagers. There is more than one path through this.
The contents of the Midlife Conversations podcast is for educational and informational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider. Some episodes of Midlife Conversations may be sponsored by products or services discussed during the show. The host may receive compensation for such advertisements or if you purchase products through affiliate links mentioned on this podcast.
The post The Circadian Rhythm and Hormone Connection with Sarah Kleiner appeared first on Natalie Jill Fitness.
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