A hidden early warning sign for dementia?

If you’ve been following me lately, you know I’ve been talking a lot about light.

Morning sunlight. Blue-light blockers at night. Eating with the sun. It’s become a real focus for me, both on the podcast and in this newsletter.

And I get it. From the outside, this stuff can look like soft interventions. Really, Dhru, do these things actually make a difference?

But here’s the thing. Circadian biology isn’t soft at all. It touches everything. Cancer risk. Autoimmunity. How well you can focus during the day. How deeply you sleep at night. Your metabolism. Your hormones. Your inflammation levels.

And now, according to a new study published in Neurology, the medical journal of the American Academy of Neurology, we can add one more thing to that list: dementia risk.

Let me walk you through what they found.

The Study

Researchers followed more than 2,000 older adults with an average age of 79 who were not showing signs or a diagnosis of dementia. Each person wore a small chest monitor for about 12 days, tracking their daily patterns of rest and activity.

This wasn’t a sleep study. They weren’t just measuring how many hours people slept. They were measuring something deeper: how strong and consistent each person’s internal clock was based on their movement patterns across the full 24-hour cycle.

Then they followed everyone for about three years to see who developed dementia.

The results were striking.

What They Found

People with weak or fragmented circadian rhythms had nearly 2.5 times the risk of developing dementia compared to people with strong, regular rhythms. Out of 727 people in the weak rhythm group, 106 developed dementia. In the strong rhythm group of 728 people, only 31 did.

The study also looked at when people’s activity peaked during the day. People whose most active time came later in the afternoon (around 2:15 p.m. or after) had a 45% higher risk of dementia compared to those who peaked earlier, between about 1:11 p.m. and 2:14 p.m.

Now, to be clear, this study shows an association, not causation. We can’t say definitively that weak circadian rhythms cause dementia. But the signal is strong enough that the researchers themselves are calling for future studies to examine whether circadian interventions, like light therapy and lifestyle changes, might actually help lower dementia risk.

Why This Makes Sense

Your circadian rhythm isn’t just about when you feel sleepy. It’s a master regulator that coordinates processes across your entire body: hormone release, body temperature, metabolism, digestion, and critically, inflammation.

When your internal clock is out of sync with the light-dark cycle, those processes can become misaligned too. The researchers suggest that circadian disruption may interfere with sleep in ways that increase amyloid plaque buildup in the brain, or reduce the brain’s ability to clear those plaques during deep sleep.

This connects directly to something I’ve written about before: your brain has a waste clearance system called the glymphatic system that’s most active during deep sleep. If your circadian rhythm is weak, your deep sleep suffers. And if your deep sleep suffers, your brain’s nightly cleanup slows down.

It all fits together.

What a Weak Circadian Rhythm Actually Looks Like

A person with a strong circadian rhythm has a clear, consistent pattern: active during the day, restful at night. Their body clock stays anchored even when their schedule shifts or the seasons change.

A person with a weak circadian rhythm has a fuzzier pattern. Their days don’t show that crisp contrast between active and restful periods. They’re more easily thrown off by schedule changes, travel, or shifts in daylight. Their body clock drifts.

If you’re the kind of person who feels like your sleep and energy are all over the place, or you find yourself staying up later and later without meaning to, that’s a sign your rhythm might be weaker than it should be.

The Good News

The amazing news is that your circadian rhythm is something you can actually influence. And the interventions are surprisingly simple.

If you're a fan of this newsletter, these won't be new to you, but they're worth repeating in the context of today's study!

Morning light is the most powerful signal. Your internal clock is set primarily by light hitting your eyes early in the day. Getting outside within the first hour of waking, even for just 15-20 minutes, helps anchor your body clock so that activity and rest align with the natural day-night cycle. This is why I make it a point to get morning sunlight while I drink my coffee, even if it’s just stepping out onto the balcony.

Consistency matters more than perfection. Going to bed and waking up at roughly the same times each day sends a strong signal to your internal clock. So does moving your body at consistent times. You don’t need a rigid schedule, but a general rhythm makes a real difference.

Reduce light at night. Bright lights and screens in the evening can push your clock later and disrupt your rhythm. I wear blue-light blockers for an hour before bed, and I dim the lights in my house after sunset. It sounds small, but it helps.

None of this is complicated. It’s just intentional!

The Bigger Picture

What I find encouraging about this research is that it points to something actionable. We’re not talking about a genetic marker you can’t change. We’re talking about daily patterns that respond to how you live.

Morning light, regular movement, consistent sleep times, and less artificial light at night. These aren’t exotic interventions. They’re the way humans lived for most of history before electricity changed everything.

Your circadian rhythm is a signal your brain pays attention to, and strengthening that signal is one of the most accessible things you can do for your long-term brain health.

And that’s not soft at all.

Here’s to your health,
Dhru Purohit

The information in this newsletter is for educational purposes only and should not be construed as medical advice; please consult a qualified healthcare professional before making any health-related decisions.