The Science of Falling Back: What Daylight Saving Time Does to Your Body Clock

On the first Sunday of November, most of the US moves its clocks back an hour - or “fall backwards” as we often call it. We tend to celebrate the extra hour of sleep, but then a few days later we notice it's dark by dinnertime and something feels a little off. So we dug into the research to see what actually happens in the body when the clocks change, and what might help.

What Daylight Saving Time (DST) Actually Is

Daylight saving time is the practice of moving clocks forward in spring so the evenings stay light longer, then back again in fall. Germany was the first country to adopt this practice in 1916, as a way to conserve fuel during World War I. The US followed in 1918, and the system we live with today grew out of the Uniform Time Act of 1966. Since 2007 it has run from the second Sunday in March to the first Sunday in November, and a couple states, Arizona and Hawaii opt out entirely.

While the clocks may change, the sun doesn’t. The total amount of daylight on any given day is the same either way. Time policy only decides which clock hours that light lands in, and that can mean the daylight your body relies on to set its internal clock is an hour out of sync, which can affect sleep and how you feel.

What the Time Change Does to Your Body

Your body keeps time with an internal clock, the circadian system, which runs on a cycle of roughly 24 hours. Light is one of the strongest cues that keeps that clock in step with the outside world.

In a systematic review of 45 studies of healthy adults, brighter morning light was linked to sleep shifting earlier, while brighter evening light was linked to sleep shifting later.¹ So when the clocks move, the light your body expects at a given moment shows up an hour off, and your internal clock has some catching up to do.

How Daylight Savings Affects Your Sleep

How big is that effect? A UK Biobank analysis used wrist accelerometers to track the sleep of 11,780 adults aged 43 to 78 around the clock changes of 2013 to 2015.² On the Sunday of the spring time change, people slept about an hour less than they had the Sunday before, around 65 minutes. In the fall, sleep on the Sunday that the clocks fell back was about 33 to 38 minutes longer, which means people picked up roughly half of the extra hour rather than all of it.

A different study came at the question from the circadian side. Using sunrise and sunset times across the US, this study modeled how much light people would get under standard time, daylight saving time, and a permanent version of each.³ They turned that into a "circadian burden," roughly how far the body clock has to stretch to keep pace with a 24-hour day, and compared those estimates with county-level health data. In the model, switching the clocks twice a year came out worst for circadian alignment, and permanent standard time came out best for most people.³ Natural early risers were the exception and did better under permanent daylight saving time.³

Based on both of these studies, a single clock change doesn't seem to wreck an entire week of sleep for most people, and the fall time change is the kinder of the two.^2,3 Where the research gets more interesting is light: when it arrives, how much of it you get, and how steady your routine stays.

How to Adjust to Daylight Savings: Nutrition and Lifestyle Strategies

You don’t need to overhaul your routine to make the time change easier. A few small, research-backed habits can help your body settle into the new schedule and reduce any disruptions the time change might incur.

Aim to Get That Extra Hour

Sleep specialists at the American Academy of Sleep Medicine suggest keeping your usual bedtime on Saturday night before DST ends, changing your clocks (if you still have manual clocks at home) at bedtime rather than earlier in the day, and getting up at your normal time on Sunday.⁴ If you hold your usual bedtime, you get the extra hour of sleep, which can really set you up for success in the days ahead.

Seek Morning Sunlight

Since light is a cue your body clock responds to, try to get some sunlight in the morning. A systematic review of 45 studies in healthy adults found that brighter morning light was associated with earlier sleep timing and better self-reported sleep.¹ A walk or reading outside is a perfectly good start, and on the contrary, don’t forget to dim the lights as the evening goes on.

If mornings are the hard part, AGZ is built with them in mind. It’s a nighttime supplement designed to support overnight restoration and help you wake up feeling refreshed in the mornings.* It includes saffron, which has been clinically shown to support a healthy mood and feeling renewed in the morning.* In one study, 75% of people taking AGZ said their morning was better than usual by Day 30, up from 54% at the start.†

Create a Restful Evening Routine

Setting yourself up for a restorative night's sleep starts before your head even hits the pillow. While your body adjusts to the new schedule, a few easy things help: dim the lights, keep your bedtime the same, and give yourself some time to wind down before bed.

AGZ also supports your evening routine. It’s a melatonin-free formula built around the evening routine, with ingredients like ashwagandha and L-theanine to help you unwind and manage daily stress.* People felt that quickly. In one study, 77% of people taking AGZ said they managed the effects of evening stress after just one night, and by Day 3, 80% noticed relaxation within 30 to 45 minutes.†

Like any routine, results compound over time with consistent use. In that same study, by Day 30, 91% felt relaxed before bed, up from 72% on Day 1, and 87% found it easier to fall asleep, compared with 26% of people taking no product.† When your nights get better, everything that follows gets better with them — your mornings, your energy, and your mood, so prioritizing the wind-down routine is important.

Get Enough Vitamin D

Shorter daylight hours and colder weather mean less sun, and sunlight is how your skin makes vitamin D. In a 12-week trial that compared women in England and Brazil through their winter months, a daily 15 microgram vitamin D supplement raised and maintained vitamin D levels.⁵

Vitamin D also supports immune and bone health.* AG1’s Vitamin D3+K2 pairs 1,000 IU (25 mcg) of vitamin D3, (125% of the Daily Value), with 100 mcg of vitamin K2 (50 mcg as MK-4 and 50 mcg as MK-7) in just two drops.* These two daily drops can easily be added to your nightly AGZ, or into any other part of your routine for support during the colder, darker months.

Putting It All Together

The extra hour of sleep is nice, but it’s the darker days that follow that are worth planning for and creating routine around. While the time change may not seem like a big deal in the grand scheme of things, that adjustment in light hours can compound as the winter months go on - which can certainly affect sleep patterns, mood, and how we feel.

So this fall be sure to keep your bedtime steady, get outside in the morning, and give yourself time to wind down at night. AGZ can help create a consistent evening routine as well as promote more restorative sleep, and AG1’s Vitamin D3+K2 is an easy way to support your routine as the days get colder and the light hours shrink.*

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

†In a third-party, open-label, randomized controlled clinical study of self-reported sleep and daytime sleepiness measures in 149 adults ages 26-59 taking AGZ over 30 days.

References:

1. Dautovich ND, Schreiber DR, Imel JL, et al. A systematic review of the amount and timing of light in association with objective and subjective sleep outcomes in community-dwelling adults. Sleep Health 2019;5(1):31-48. doi:10.1016/j.sleh.2018.09.006
2. de Lange MA, Richmond RC, Birnie K, Shapland CY, Tilling K, Davies NM. The effects of daylight saving time clock changes on accelerometer-measured sleep duration in the UK Biobank. J Sleep Res 2025;34(3):e14335. doi:10.1111/jsr.14335
3. Weed L, Zeitzer JM. Circadian-informed modeling predicts regional variation in obesity...under different permanent US time policies. Proceedings of the National Academy of Sciences 2025;122(38). doi:10.1073/pnas.2508293122
4. Quinn T. ‘Fall back’ should be the last clock change, sleep experts tell lawmakers. American Academy of Sleep Medicine – Association for Sleep Clinicians and Researchers October 7, 2026. Accessed October 16, 2026. https://aasm.org/fall-back-should-be-the-last-clock-change-sleep-experts-tell-lawmakers/
5. Mendes MM, Hart KH, Williams EL, Mendis J, Lanham-New SA, Botelho PB. Vitamin D Supplementation and Sunlight Exposure on Serum Vitamin D Concentrations in 2 Parallel, Double-Blind, Randomized, Placebo-Controlled Trials. The Journal of Nutrition 2021;151(10):3137-3150. doi:10.1093/jn/nxab209