Dr Martin Moore-Ede is a former Harvard Medical School professor, leading circadian clock researcher, and Chief Health Advisor at LightHealth. He discovered the suprachiasmatic nucleus, the biological clock in the human brain, and has spent over 40 years studying how light governs human health.
Something unusual has been happening to cancer statistics. For decades, cancer was understood primarily as a disease of age. The older you were, the higher your risk. But over the past two decades, rates of certain cancers in people under 50 have been rising sharply, including breast cancer, colorectal cancer, and thyroid cancer. The trend is consistent enough across countries that researchers are now asking what changed, and when.
One candidate that deserves serious attention is the lighting in our homes.
The timing of the shift
The rise in early-onset cancers maps closely onto a technological transition: the mass adoption of blue-rich LED lighting and the explosion in evening screen use. This does not prove causation. But the timeline is striking, and the biological mechanism is well established.
Melatonin, the hormone produced by the pineal gland during darkness, is not simply a sleep signal. It is one of the body's most powerful antioxidants and plays a direct role in regulating cell proliferation and immune surveillance. As we explore in our piece on how much light harms health at night, even low lux levels suppress this crucial hormone. When melatonin production is suppressed or shortened, the biological systems that normally identify and clear aberrant cells are compromised.
What blue light does at night
Blue-range light, peaking around 480nm and dominant in modern white LED bulbs and screens, signals to the brain that it is still daytime. The pineal gland delays or reduces melatonin production accordingly.
This is not a new finding. The carcinogenic potential of light at night has been studied extensively, particularly in shift workers whose melatonin cycles are chronically disrupted. The International Agency for Research on Cancer classified night shift work as a probable carcinogen in 2007. What has changed is that billions of people now effectively live a version of shift work biology in their own homes, every evening, through their lighting and screens. For the broader evidence linking light exposure to long-term health outcomes, see our piece on could more sunlight help you live longer.
The evidence we should take seriously
Several large epidemiological studies have found associations between habitual exposure to artificial light at night and elevated rates of breast and prostate cancer. Animal studies have shown that disrupting circadian light cycles accelerates tumour growth. The evidence is not yet the kind that makes clinical headlines, but it is consistent, mechanistically plausible, and accumulating.
This does not mean that LED lights are the only explanation, or even the primary one. Diet, sedentary behaviour, microbiome changes, and environmental toxins all likely play a role. But light is a modifiable factor, and one that has received far less attention than it deserves.
A simple change with a plausible benefit
Restoring the biological night, meaning genuine darkness or amber-only wavelengths in the hours before sleep, is achievable with the right lighting. It costs nothing in terms of lifestyle disruption and carries no downside. Whether or not the cancer connection proves as strong as the epidemiology suggests, the case for removing blue light from your evenings is already well supported by the sleep, metabolic, and hormonal evidence alone. For practical guidance on choosing the right lighting for each room and time of day, see what to ask before you switch on the lights.
The lights we install in our homes are not neutral. They carry a spectrum, and that spectrum matters.
