Seasons & latitude
Our biology was set under strong, steady sunlight. Northern winters ask a lot of it, but there’s plenty you can do.
THE BIG IDEA
We evolved for a different sky
For almost all of human history our ancestors lived under strong sunlight, much closer to the equator. As Glen Jeffery puts it, many of us now live much further north, with short winter days, grey weather and lives spent mostly indoors. The effects show up in the data. Death rates in places like Norway and Scotland are around a quarter higher in midwinter than in late summer, with heart disease a big part of the difference.
HOW IT WORKS
Why latitude matters
1
The sun sits lower
Further from the equator, the winter sun stays low in the sky, so its light passes through more atmosphere and brings almost no UV.
2
The days get short
In northern Europe winter daylight shrinks to a few hours, and much of it falls while we’re at work or school.
3
We retreat indoors
Cold weather means more clothes and more time inside, cutting our light exposure just when it’s scarcest.
WHAT THE SCIENCE SAYS
The numbers behind the idea
~25%
Higher death rates in midwinter than in late summer in Norway and Scotland, with heart disease driving much of the difference.
30–40%
Lower risk of blood clots for each sun habit Swedish women reported, including a winter sun holiday, in Pelle Lindqvist’s research.
Mirror image
Deaths from all causes peak just after Christmas in the northern hemisphere and at the end of June in the southern, as Glen Jeffery points out.
~3 years
The gap in life expectancy between Australia and the UK, much of it linked to heart disease, according to GP Torkil Færø.
FROM THE PODCAST
In their own words
Prof. Glen Jeffery
UCL Institute of Ophthalmology
Prof. Pelle Lindqvist
Professor and senior consultant, Stockholm
David Herrera
Coach, ‘The Solar Athlete’, on winter
WHAT YOU CAN DO
Make the most of the light you have
Chase the winter sun
Get outside around midday on bright winter days, when the light is at its strongest.
Plan a trip south
If you can, a week or two somewhere sunnier in winter gives your body a real boost.
Brighten your indoor light
Use broad-spectrum lamps at home in the darker months, and sit by the brightest window.
Ease back in each spring
As the days lengthen, build up your time in the sun gradually so your skin is ready for summer.
Put it into practice
Find the sun in winter
Shadowmap shows which streets, parks and squares still get direct sun on short winter days, so you know exactly where to find it.
KEEP READING
More health guides
Explore how light shapes other parts of your health, from your cells to your sleep.
Light & your cells
How infrared light from the sun helps the energy factories in your cells run more smoothly.
Read the guide →
Light & mood
Why bright days and dark nights are linked to a lower risk of depression.
Read the guide →
Body clock & sleep
How morning light, dark evenings and a strong daily rhythm keep your body in sync.
Read the guide →
Sources & further listening
Fosbury R., Seheult R., Zimmerman S. & Jeffery G., ‘Editing the Sun: how indoor light lost touch with biology’ (2026). Pelle Lindqvist and colleagues, sun exposure and venous thromboembolism in Swedish women. Sunlight Matters podcast episodes with Pelle Lindqvist, Glen Jeffery, David Herrera and Dr Torkil Færø, author of ‘The Sun Cure’. This page is general information, not medical advice.
