Hour Lost To Daylight Saving Time Linked To Vision-Stealing Eye Diseases

Every March, clocks spring forward for daylight saving time and Americans who observe it lose an hour of sleep. That single lost hour is easy to write off as a minor inconvenience, a groggy Monday and one too many cups of coffee. But a sweeping new study suggests that lost hour may be associated with something far more serious: a higher chance of developing dangerous eye diseases that have the potential to permanently damage vision.

Researchers examined health insurance records from more than 12.6 million privately insured adults between the ages of 18 and 64 and found that the spring daylight saving time transition was linked to a notably higher chance of a new diagnosis of proliferative diabetic retinopathy (PDR) and neovascular age-related macular degeneration (nvAMD) in the following month, relative to a summer control period. Meanwhile, the autumn “fall back” transition, when people gain an hour, appeared protective in several comparisons, associated with lower risk of multiple eye diseases. Their results appear in the journal Scientific Reports.

At first glance, the idea that resetting a clock could affect eyesight sounds far-fetched. But researchers say the explanation runs deeper than just feeling tired. Losing even one hour of sleep throws off the body’s internal clock, the finely tuned biological system that governs inflammation, blood pressure, and blood sugar levels. The tiny blood vessels inside the eye, it turns out, are highly sensitive to exactly those kinds of disruptions.

What Researchers Found About Daylight Saving Time and Eye Disease

To conduct the study, researchers pulled data from a massive collection of private health insurance claims. They focused on commercially insured adults between the ages of 18 and 64 enrolled between 2012 and 2014, ending up with a study group of 12,640,343 people, a sample large enough to detect even subtle patterns. Participants were about 42 years old on average, and about 56% were female. Because the database was limited to privately insured adults under 65, the results may not apply to older adults, those on public insurance, or the uninsured, an important caveat since eye diseases like macular degeneration become far more common with age.

Researchers tracked how many patients received a brand-new diagnosis of four specific eye diseases in the weeks following each clock change: blockages in the arteries supplying the retina; blockages in the retinal veins; an advanced form of diabetic eye disease where abnormal blood vessels grow inside the eye and can cause blindness; and an aggressive form of macular degeneration, a disease that destroys the sharp central vision people rely on for reading and recognizing faces.

To establish a fair comparison, the team measured new eye disease diagnoses after the spring and fall clock changes and also during control periods in summer and winter when no time change occurred. Their statistical models accounted for age, sex, smoking history, pre-existing conditions like high blood pressure and high cholesterol, heart disease history, and known sleep disorders.

How Daylight Saving Time’s Spring Shift Raises Eye Disease Risk

Springing forward produced the most notable findings. In the month after clocks sprang forward, the risk of developing advanced diabetic eye disease rose by 34% compared to a summer control period. The risk of developing the aggressive form of macular degeneration rose by 24% compared to that same period. Significant results showed up mainly at the one-month mark rather than in the first week, a pattern the authors read as evidence that structural changes in blood vessels likely take weeks to appear. They caution that the precise reason behind this delayed effect remains unclear.

Autumn’s transition told a different story. Compared to a summer control period, the month after clocks fell back was associated with a 16% lower risk of retinal vein blockages and a 17% lower risk of advanced diabetic eye disease. Compared to a winter control period, the protection was broader: a 25% lower risk of retinal artery blockages, a 34% lower risk of vein blockages, a 39% lower risk of advanced diabetic eye disease, and a 36% lower risk of the aggressive form of macular degeneration.

Researchers believe this pattern mirrors what has been seen with heart attacks and strokes around daylight saving time transitions. Prior research has shown that losing sleep, even just one hour, can trigger the body to produce more stress hormones, raise blood pressure, worsen blood sugar control, and promote inflammation throughout the body. All of those changes can damage small blood vessels, including the intricate network that keeps the retina alive and functioning. Gaining an hour, by contrast, was associated with a possible protective effect in several comparisons, though the authors caution that the mechanism behind that association, and why it did not appear uniformly across all outcomes, remains unclear and speculative.

Who Is Most at Risk From the Spring Time Change

Among the risk factors identified in the study, a few stood out as especially powerful. People who already had early-stage diabetic eye disease were dramatically more likely to develop the advanced, vision-threatening form after the spring time change. Similarly, people with an earlier, less severe form of macular degeneration faced a sharply elevated risk of progressing to the more dangerous version. Other risk factors for new eye disease around the time changes included older age, high blood pressure, high cholesterol, and a history of heart disease or stroke.

One somewhat unexpected finding also emerged: diagnosed sleep disorders, including sleep apnea and insomnia, were not significantly associated with increased eye disease risk around the time changes in this claims-based analysis. Researchers offer a few possible explanations. People being treated for sleep disorders may have some protection from a short-term disruption. Sleep disorders may also be under-reported in insurance claims data, making it difficult to detect an association even if one exists. Or chronic, long-term sleep disruption may simply affect the body differently than the sudden jolt of losing one hour.

Daylight saving time has been debated for years on public health grounds, with previous research linking the spring transition to increased rates of heart attacks and strokes. This work extends that conversation to the eyes. For the millions of Americans with diabetes or early macular degeneration, the authors suggest that the spring clock change may act as a recurring window of heightened vulnerability, and that patients at higher risk for disease progression who become newly symptomatic around that time may warrant more prompt evaluation. These are the researchers’ conclusions based on an observational study; readers should consult their own physicians about personal risk.

Disclaimer: This article summarizes an observational study and is for general information only. It is not medical advice. The research shows a statistical association between daylight saving time transitions and new eye-disease diagnoses; it does not prove that changing the clocks causes eye disease. Anyone with concerns about their vision or personal risk should consult a qualified physician.

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