Getting Less Than This Much Sunlight During the Day May Increase Your Dementia Risk, Scientists Find

• Scientists have found new evidence suggesting that our light exposure may have consequences for our brain health.
• In a recent study, people who were exposed to less than 42 minutes of daylight per day were 17% more likely to develop dementia.
• Here’s what a neurologist says about the findings.

Days after the end of daylight saving time, many of us are probably still feeling a bit off as we adjust to fewer hours of daylight. There’s a reason for this: Research shows that getting enough exposure to daylight is key to how our brains function.

In fact, as a recent study published in General Psychiatry suggests, not reaching a certain threshold may actually have major consequences for our brain health.

Meet the expert: David Perlmutter, M.D., F.A.C.N., A.B.I.H.M., board-certified neurologist and NYT bestselling author ofBrain Defenders.

The researchers tracked daytime light exposure for 87,577 dementia-free participants over the course of a week-long period using data from their wrist trackers. Then, over a follow-up period of about eight years, they compared those findings to the number of participants who were diagnosed with dementia.

The results showed that the people who were exposed to at least 0.7 hours (about 42 minutes) of bright daylight per day on average were about 17% less likely to develop dementia than people who received less daylight. That link remained significant even after the researchers accounted for physical activity, diet, obesity, and cardiovascular health—all factors that influence our dementia risk.

Ahead, a neurologist breaks down the findings—and how you can work them into your day-to-day.

Why are the findings significant?

Modern life and technology offer plenty of ways for us to manipulate the light we’re exposed to throughout the day and night—whether you’re prone to scrolling on your phone in bed or rely on a sunrise alarm clock to start your day. But the findings show that light cues may have long-term consequences for our cognitive health, according to David Perlmutter, M.D., F.A.C.N., A.B.I.H.M., board-certified neurologist and NYT bestselling author ofBrain Defenders.

“The significance here extends well beyond the specific number of minutes,” he says. “We are beginning to recognize that our brains and bodies are profoundly influenced by environmental signals, including light, that regulate fundamental biological processes.”

For Dr. Perlmutter, the takeaway is that our understanding of what it means to live a brain-healthy lifestyle needs to expand. “We appropriately emphasize nutrition, exercise, sleep, and social connection, but light exposure deserves a place in this conversation,” he explains. “One particularly fascinating finding was that the association between bright daytime light and reduced dementia risk appeared even stronger among individuals carrying the APOE4 gene variant, which increases risk for Alzheimer’s disease.”

That’s a distinction worth paying attention to. “Our genes influence our susceptibility, but our daily choices and environmental exposures can profoundly influence how that susceptibility plays out,” Dr. Perlmutter explains.

Why might light exposure affect brain health?

The researchers speculated that the protective benefit may be due to the effect of light exposure on the fusiform cortex and other structures in the brain that deal with our rest and activity rhythms. As Dr. Perlmutter explains, our brain’s master circadian clock is activated by light entering our eyes. “This system helps coordinate sleep-wake cycles, hormonal signaling, metabolism, and numerous processes essential for maintaining brain health,” Dr. Perlmutter says.

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When our circadian rhythms are properly synchronized, we usually are able to get more restorative, high-quality sleep, which is when our brain undergoes important cellular maintenance and removes metabolic waste, according to Dr. Perlmutter. A regulated circadian rhythm also helps us manage inflammation and supports our immune function. A buildup of excess waste and inflammation that the brain isn’t able to “clean up” during sleep could eventually contribute to cognitive problems—including dementia—down the road.

That’s because “the brain’s resident immune cells, called microglia, respond to metabolic and environmental signals,” he explains. Some research suggests that when our circadian rhythm is disrupted, it can make these cells behave differently. “While this study did not directly measure microglial function, it provides another compelling reason to investigate how environmental light might influence the brain’s immune and metabolic health,” he says.

One important callout: The participants’ vitamin D levels didn’t affect the findings either way, a fact Dr. Perlmutter describes as both interesting and surprising. This may indicate that “the benefits associated with daylight may involve much more than vitamin D production,” Dr. Perlmutter points out.

What does this mean for you?

“My recommendation is straightforward: Make exposure to natural daylight an intentional part of your daily routine, just as you would exercise or healthy eating,” Dr. Perlmutter says. “Ideally, get outside in the morning, when light exposure can help synchronize the body’s internal biological clock.” If you want to soak up some daylight and get some exercise—another important habit for brain health—he suggests making a morning walk part of your routine.

With daylight hours becoming shorter as winter approaches, Dr. Perlmutter says getting light in when you can becomes even more important. “Try to schedule outdoor activities during available daylight, take breaks outside during the workday, and maximize natural light entering your home or workplace,” he suggests. If that’s not realistic for you or you live in a climate where daylight is hard to come by, he says investing in a device designed to mimic sunlight, like a light therapy lamp, can help, although there’s no evidence suggesting these can prevent dementia.

Dr. Perlmutter also warns against getting too caught up in that 42-minute threshold highlighted in the study. “[It] should not be interpreted as a magical cutoff beyond which the brain suddenly becomes protected. It’s a statistical finding that requires further investigation.” Instead, just focus on getting outside when you can.

But while the goal is to get more light exposure, know that there is such a thing as going overboard. “Protecting the eyes from excessive ultraviolet exposure remains essential,” Dr. Perlmutter warns. “The goal is not prolonged sunbathing or staring at the sun. Rather, it is providing the brain with the natural environmental signals that help regulate its biology.”

And remember that being mindful of your light exposure is just one of many ways to promote brain health. “I encourage people to adopt a comprehensive approach to protecting their brains,” Dr. Perlmutter says. That means getting regular exercise, eating a diverse diet of nutritionally rich foods, getting enough good sleep, maintaining meaningful social connections, and avoiding smoking.

The bottom line

The results of the study point toward a simple, affordable, and accessible way to protect our brains, but there’s more to consider. As an observational study, Dr. Perlmutter points out that the researchers were able to identify associations between light exposure and dementia, but not a cause-and-effect relationship. Other factors, like exercise, diet, and social engagement, may also play a role in that relationship.

And using a wrist-worn device to measure the participants’ light exposure may also have limitations, since it “may not accurately reflect an individual’s long-term exposure or the amount of light actually reaching the eyes,” he says.

Still, Dr. Perlmutter says there’s reason to be optimistic. “Ultimately, the central message is one of empowerment. We cannot guarantee that any individual will avoid [dementia or Alzheimer’s disease], but we can meaningfully influence many of the biological pathways associated with brain aging,” he says. “This new research suggests that something as simple as stepping outside into the daylight may be another valuable part of that effort.”

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