The Indoor Generation
A child born in Britain in 2025 will, on current trends, spend less of their life outside than any human being who has ever lived. This is not a moral judgement. It is just a description. The shift has happened slowly enough, and inside enough lives, that nobody has really noticed it — but it has happened.
The phrase "the indoor generation" started showing up in the late 2010s, mostly in research commissioned by window manufacturers and air-quality companies. Easy to dismiss as marketing language. Harder to dismiss when you read the actual numbers behind it. Adults in industrialised countries now spend, on average, around 90% of their lives indoors. Most do not consider this remarkable. It is just how life is arranged now.
The biological consequences of this slow withdrawal from outdoor life are starting to show up in places we did not used to look.
Curious whether your indoor life is leaving you short on the basics? Take our two-minute quiz for a personalised view, or read about Daily Sunshine, our daily formula for British indoor living.
The 90% statistic in context
The figure comes most prominently from a 2018 study commissioned by VELUX across 14 countries. It is corroborated by the US Environmental Protection Agency's National Human Activity Pattern Survey, which found Americans spent 87% of time inside buildings plus another 6% inside vehicles. The British numbers, given the climate, are almost certainly slightly worse in winter.
That figure means the average person spends roughly two hours per day in any form of outdoor light. Of those two hours, most are spent in transit — on the way to or from something else. The amount of time spent simply being outdoors, on the ground, exposed to sky, has collapsed to something close to zero for many adults.
What we evolved for
For most of human history this would have been incomprehensible. The agricultural societies that produced almost everyone reading this article ran on outdoor labour, outdoor commerce, outdoor weather. The industrial revolution moved a chunk of that indoors, but the industrial worker still walked to the factory, ate lunch on a street, walked home. The post-war suburb still meant a garden and a shop down the road. Even the 1990s office worker, sealed in fluorescent lighting most of the day, had to physically get there.
The body did not get a memo about any of this. Its operating system was developed over hundreds of thousands of years of life lived under the sky. The circadian rhythms that organise sleep, the skin's machinery for making vitamin D from UVB, the hormonal cascades triggered by daylight on the retina — all of it assumes a baseline level of outdoor exposure that, for most adults in 2026, no longer happens.
The quiet biological cost
The most obvious downstream effect is vitamin D. The UK's Scientific Advisory Committee on Nutrition reported in 2016 that diet alone supplies only a fraction of most people's vitamin D needs — the primary route is skin synthesis from UVB. If you spend 90% of your life indoors, the production line is essentially closed. The UK's National Diet and Nutrition Survey finds about one in five adults runs deficient through winter.
Less obvious but probably equally important: indoor lighting, even bright indoor lighting, is a poor signal to the circadian system. An overcast outdoor day delivers around 10,000 lux. A well-lit office gives you 300 to 500. Researchers at Harvard Medical School have spent decades demonstrating that indoor light is, in technical terms, insufficient for proper entrainment. Translation: your body clock drifts when you do not see the sun.
Then there is the mood piece. Bright light exposure is the basis of the established treatment for Seasonal Affective Disorder. The Royal College of Psychiatrists notes around 2 in every 100 UK adults meet diagnostic criteria for SAD, with many more experiencing milder "winter blues". The treatment for SAD is, essentially, outdoor light at a higher intensity than indoor light. The condition itself is, essentially, a deficiency of the same.
It is not a generational moral failing
One trap to avoid here is the move toward blaming individuals. The indoor generation did not choose to be indoor. The infrastructure choices that produced this outcome were collective — remote working, food delivery, screen-based entertainment, climate-controlled buildings, the steady disappearance of casual outdoor friction from daily life. Each individual change is rational. The aggregate is a generation that has, without quite meaning to, taken itself indoors.
That is also why the fix is not dramatic. You do not need to move to a cabin. You need ten minutes of outdoor light in the morning, a window seat at lunch when you can, calls taken on a walk where possible, and — for the bit your skin genuinely cannot manage in winter — a daily vitamin D supplement, as the NHS recommends from October to March.
If you are a card-carrying member of the indoor generation, the easiest single intervention is the one your physiology cannot do for itself in winter. Daily Sunshine closes that specific gap. Take our quiz to see if it makes sense for you.
The point
None of this is an argument that modern life is wrong. It is an argument that the way most of us now live is structurally light-poor and outdoor-poor — quietly, almost invisibly so — and that the body, which did not get any of the memos, is still operating on a much older set of expectations.
The indoor generation is not a problem to be felt guilty about. It is a description of where we are. The work, such as it is, is in noticing it — and in making the small daily moves that keep the body roughly in sync with a world it never quite caught up with.
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