2024Nature Mental Health
Windred et al.
86,772 UK Biobank adults, light sensors
Brighter nights raised the risk of depression, anxiety and other psychiatric conditions; brighter days lowered it.
Find on PubMed ↗Research library · Tech & environment
Light, air and nature: your environment's hidden effects
Your surroundings shape your health every hour. Daylight sets your body clock, light at night disrupts it, polluted air shortens lives worldwide, and time in nature lowers stress. Most of these are easy to adjust.
Good evidenceUpdated Oct 2026 · 4 new studies+30%depression risk in people with the brightest nights; bright days cut it by about 20%Windred 2024, Nat Mental Health, 86,772 adults
2.9 yrsof average life expectancy lost worldwide to air pollution, more than to smokingLelieveld 2020, Cardiovasc Res
120 mina week in nature linked to better health and wellbeingWhite 2019, Sci Rep, 19,806 adults
01
The basics
The world around you is a health input
A master clock in your brain (the suprachiasmatic nucleus) keeps your body on a 24-hour cycle. Special light sensors in your eyes (melanopsin cells) reset it each day. Outdoor light is 10,000–100,000 lux; indoor light is often only 100–500. Bright days and dark nights give a strong, steady rhythm for sleep, hormones and mood.
Tiny particles in polluted air (PM2.5) pass deep into your lungs and blood, inflaming arteries and raising the risk of heart attacks, strokes, lung disease and dementia. Indoor air matters too: gas cooking, wood burners and poor ventilation add pollution.
Newer concerns include microplastics, which a 2024 study found inside artery plaques, linked to higher heart risk. Meanwhile, time in green and blue spaces (parks, forests, coasts) is consistently linked to lower stress and better mental health.
How much light you really get
Illustration of a day outdoors versus a typical indoor day. Indoors, days are dim and evenings bright, which weakens your body clock's signal.
02
How it works
How light sets your body clock
1
Morning daylight
Bright light within an hour of waking is the strongest clock signal.
2
Eye sensors fire
Melanopsin cells send the signal to your brain's master clock.
3
Clock resets
Cortisol rises in the morning; body temperature and alertness follow.
4
Melatonin on time
About 14–16 hours later melatonin rises, if evenings stay dim.
03
Measure it
Measuring your environment
- Light: phone light-meter apps give a rough lux reading. Aim for outdoor-level light in the morning and under 10 lux in the bedroom at night.
- Outdoor air: check the Air Quality Index (AQI) in your weather app.
- Indoor air: a CO₂ monitor shows ventilation; above 1,000 ppm means open a window.
- Noise: traffic noise at night above about 45 dB is linked to poor sleep and higher blood pressure.
Try your number
GoodModerateSensitive groupsUnhealthy
0300
US EPA Air Quality Index. On bad days, exercise indoors, close windows and run a HEPA filter.
04
What the research says
The key studies
2020Cardiovascular Research
Lelieveld et al.
Global model
Air pollution cut average world life expectancy by 2.9 years, more than tobacco (2.2 years) or HIV (0.7 years).
Find on PubMed ↗2019Scientific Reports
White et al.
19,806 adults in England
People spending 120+ minutes a week in nature were more likely to report good health and wellbeing. It didn't matter how the time was split.
Find on PubMed ↗2024NEJM
Marfella et al.
257 adults having artery surgery
Microplastics were found in the artery plaques of more than half. They had 4.5 times the risk of heart attack, stroke or death over about 3 years.
Find on PubMed ↗2013Current Biology
Wright et al.
8 adults
A week of camping with only natural light shifted people's body clocks about 2 hours earlier and synced melatonin with sunset.
Find on PubMed ↗05
New in 2025–26
What the newest research adds
Bright light at night, polluted air and frequent extreme heat are all now linked to heart disease, dementia or faster ageing in large studies. Claims about microplastics building up in the brain are worrying but the measurements are being questioned.
The new studies, in order
Every study added to this page since January 2025. Green rings are the strongest evidence: large trials or meta-analyses.
Light at night and the heart
Windred et al., 2025. 88,905 people wore light sensors. Risk for the brightest nights compared with the darkest (1 = no difference).
NewOct 2025JAMA Network Open
Windred et al.
88,905 UK Biobank adults wearing light sensors, 9.5 years
People with the brightest nights had 47% higher risk of heart attack and 56% higher risk of heart failure than those with the darkest nights. Keeping the bedroom dark is a simple step.
Good evidenceRead the source ↗
NewJul 2025Lancet Planetary Health
Rogowski, Bredell et al.
51 studies, more than 29 million people
Every 10 µg/m³ more fine particle pollution (PM2.5) in the air was linked to about 17% higher risk of dementia. Soot from traffic was linked to 13% higher risk per 1 µg/m³.
Strong evidenceRead the source ↗
NewFeb 2025Science Advances
Choi and Ailshire
3,600+ US adults aged 56+, 6 years
Older adults living where extreme heat days are common (about half the year) showed up to 14 months of extra biological ageing in their blood, compared with those in places with fewer than 10 heat days a year.
Good evidenceRead the source ↗
NewFeb 2025Nature Medicine
Nihart et al.
Brain, liver and kidney tissue from 2016 to 2024
Brain samples from 2024 held about 50% more micro- and nanoplastics than those from 2016, with higher levels in people with dementia. Germany's risk agency (BfR) says the amounts look implausibly high and may include false signals from brain fat, so these numbers need checking.
Early evidenceRead the source ↗
What this changes for you
Make your bedroom properly dark (blackout blinds, no screens), keep daytime light bright and outdoors, use a cooker hood or open a window when cooking, and check air-quality alerts on bad days.
06
Take action
Shaping a healthier environment
A few changes at home and in your routine shift your daily exposure a lot.
- 1
Get outside within an hour of waking
10–30 minutes of daylight, longer on cloudy days. No sunglasses for part of it, but never look at the sun.
- 2
Dim the evening
Lower lights and screens 2 hours before bed; keep the bedroom dark.
- 3
2 hours a week in nature
Parks, woods, rivers or coast, split however suits you.
- 4
Clean your indoor air
Use the cooker hood, open windows after cooking and run a HEPA filter in polluted areas.
- 5
Keep the bedroom cool
Around 16–19 °C helps most people sleep.
- 6
Heat food in glass, not plastic
A simple precaution while microplastic research develops.
07
Myth or fact
Common myths, checked
✕ MythBlue light from screens is the main sleep problem.
✓ FactOverall brightness, timing and what you're doing on the screen matter more than the colour.
✕ MythIndoor air is always cleaner.
✓ FactCooking, candles, gas stoves and poor ventilation can make indoor air worse than outside.
✕ MythCloudy days don't count for light.
✓ FactAn overcast sky still gives 1,000–10,000 lux, far more than indoor lighting.
✕ MythAir purifiers are a gimmick.
✓ FactHEPA purifiers measurably reduce indoor particles, especially from wildfire smoke and traffic.
08
Questions
Frequently asked
Do light therapy lamps work?
Yes for winter depression (SAD): about 10,000 lux for 20–30 minutes in the morning. Check with a doctor if you have eye conditions or bipolar disorder.
Should I wear a mask on smoggy days?
A well-fitted N95/FFP2 mask filters fine particles if you must be outside.
Does living near a main road matter?
Yes. Pollution and noise are linked to higher heart and lung risk. Keep windows on the quieter side open where possible.
09
Test yourself
True, partly true or myth?
Read each claim and pick an answer: the card flips to show the verdict and why. Not sure? Use “Just reveal”.
Card № 01True or myth?
Air pollution is one of the biggest environmental causes of early death worldwide.
True
Air pollution is one of the biggest environmental causes of early death worldwide.
Fine particles (PM2.5) are linked to heart disease, stroke, lung cancer and dementia.
Card № 02True or myth?
Morning daylight helps set your body clock.
True
Morning daylight helps set your body clock.
Light in the first hours after waking strengthens your circadian rhythm and can improve sleep at night.
Card № 03True or myth?
Indoor light is as bright as daylight.
Myth
Indoor light is as bright as daylight.
Indoor light is often 100–500 lux; outdoor daylight is 10,000 lux or more, even on cloudy days.
Card № 04True or myth?
Bright light at night is linked to worse sleep and metabolism.
True
Bright light at night is linked to worse sleep and metabolism.
Large UK Biobank studies link more night light exposure to higher risk of diabetes and mental health problems.
Card № 05True or myth?
Indoor air purifiers improve health.
Partly true
Indoor air purifiers improve health.
HEPA filters reduce particles and may lower blood pressure slightly; long-term health effects need more study.
Card № 06True or myth?
Living near green space is linked to longer life.
True
Living near green space is linked to longer life.
Studies across many countries link more greenery to lower death risk and better mental health.
Card № 07True or myth?
Noise only matters if it wakes you up.
Myth
Noise only matters if it wakes you up.
Traffic noise at night raises stress hormones and blood pressure even when you sleep through it.
Card № 08True or myth?
Gas cooking can raise indoor nitrogen dioxide levels.
True
Gas cooking can raise indoor nitrogen dioxide levels.
Good ventilation or extractor fans while cooking reduce exposure.
Card № 09True or myth?
Extreme heat is mainly risky for older people.
Partly true
Extreme heat is mainly risky for older people.
Older adults are most at risk, but heat also harms outdoor workers, athletes, babies and people with chronic illness.
Card № 10True or myth?
Sunlight through a window gives you vitamin D.
Myth
Sunlight through a window gives you vitamin D.
Glass blocks most UVB, the rays your skin needs to make vitamin D.
Nothing here yet. Try another filter.
10
Sources
References and related topics
- Windred et al. (2024). Nature Mental Health. 86,772 UK Biobank adults, light sensors. PubMed ↗
- Lelieveld et al. (2020). Cardiovascular Research. Global model. PubMed ↗
- White et al. (2019). Scientific Reports. 19,806 adults in England. PubMed ↗
- Marfella et al. (2024). NEJM. 257 adults having artery surgery. PubMed ↗
- Wright et al. (2013). Current Biology. 8 adults. PubMed ↗
- Windred et al. (2025). JAMA Network Open. 88,905 UK Biobank adults wearing light sensors, 9.5 years. Source ↗
- Rogowski, Bredell et al. (2025). Lancet Planetary Health. 51 studies, more than 29 million people. Source ↗
- Choi and Ailshire (2025). Science Advances. 3,600+ US adults aged 56+, 6 years. Source ↗
- Nihart et al. (2025). Nature Medicine. Brain, liver and kidney tissue from 2016 to 2024. Source ↗