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SCIENTISTS HAVE DRAWN a clear link between street lights and other outdoor artificial light at night and depression – including in Ireland.
The research drew on data from major population surveys of older adults in Ireland, Northern Ireland, the UK and the US – with the same strong association found in all countries.
The research led by University College London mapped individuals with depressive symptoms against satellite data on outdoor light.
It adds to a growing body of evidence on the impact of the environment in which we live on our mental health – including the impact of artificial light, which has enhanced human activity, productivity and safety at night but has had unintended consequences.
Body clock
This study didn’t examine the precise mechanism by which artificial light affects us, but the team’s working hypothesis is that excessive exposure to light at night disrupts the body’s circadian rhythm – our natural 24-hour clock.
Lead researcher Paola Zaninotto explained: ”This is disrupting [sleep hormone] melatonin and disturbing the sleep, and weakening the normal regulation of the sleep-wake cycle – and in general, it has been shown that this disruption to the circadian rhythm and disruption to sleep together are risk factors for depression.”
This study’s data and findings are for people aged 50 and older – but the same biological mechanism is relevant across all age groups. It also applies to both indoor and outdoor exposure to light.
Other studies have found this in a younger population, although in younger people there may also be other factors at play, Zaninotto said.
People with chronic conditions, existing mental health problems or sleep problems are likely to be particularly at risk of depression when exposed to more artificial light at night. Because ageing disrupts circadian regulation, older people are also likely to be particularly at risk.
Zaninotto said the team were surprised by the consistency of their results across the different countries.
“I was expecting a bit more difference, especially when we looked at the United States which is geographically very different from the UK and Ireland – but the results were very consistent,” she said.
The researchers controlled for another environmental factor associated with depression, the vehicle exhaust pollutant NO2, and still found the same results. They also controlled for the amount of green space in the local environment, which is known to be associated with better mental health.
The researchers couldn’t assess people’s exposure to indoor sources of light such as smartphones, TV screens and bright bedroom lights, however.
In Ireland, a stronger effect was found for rural populations. This could be due to people in urban areas being more likely to use black-out curtains, sleep masks or other “adaptive behaviours”, the study suggested.
Black-out curtains
Zaninotto said while she obviously can’t give medical advice, people should understand that there are many factors which influence our mental health, and exposure to light at night, whether indoor or outdoor, is one which has been overlooked for a long time.
“I think we need to become a bit more aware that this is something that is not part of our natural cycle. Over time, repeated exposure can have an impact on many different aspects of our life including our mental health.
Putting up black-out curtains – which block outdoor light – and being careful about how much artificial night you are exposed to in a given week are “little things we can all look out for”, she said.
The research was published in the journal Environment International.
