A big wake-up call and this is no light-hearted stuff. Ok. Bad puns. But, worth paying attention, even if, as a scientist told me, that “large epidemiological studies have either found or not found a correlation between breast cancer rates and night shift.”
A growing body of evidence shows that light pollution exacerbates, and might directly cause, cancer, obesity, and depression, the troublesome triumvirate of industrialised society. One of the first people to notice this correlation, at least as it applies to cancer, is Richard Stevens, a professor at the University of Connecticut, respected cancer epidemiologist, and mild insomniac. In the early 1980s, Stevens and other researchers were beginning to realise there was little or no connection between diet and rising rates of breast cancer, contrary to what had been suspected. As Stevens puts it, it was like a light bulb going on when he realised that, in fact, a light bulb going on might be a culprit.
His 1987 paper ‘Electric Power Use and Breast Cancer: A Hypothesis’ was one of the first to report the potential connection between rising cancer rates and artificial night-time light exposure, something he and others have continued to report in the intervening 27 years.
Melatonin has the same basic function in people, birds, fish, amphibians, and other mammals. Production of melatonin should begin at dusk, when we are supposed to sleep. Light – not wakefulness itself, but light – shuts it off, as Stevens emphasised to me.
When we sleep according to a solar cycle, melatonin production follows this pattern, rising with the night. But artificial light tamps it down.
In 2007, Belgian researchers surveyed 1,656 teenagers about their use of mobile phones after lights-out, and found those who used a phone less than once per week were more than twice as likely to be ‘very tired’ a year later as those who never did. Using a phone after lights-out about once a week increased the risk of being ‘very tired’ by five times.
Shift workers, who rise with the night and work awash in blue light, experience not only disrupted circadian rhythms and sleep deprivation, but an increased risk of breast and prostate cancer. These cancers, which require hormones to grow, are suppressed in the presence of melatonin, Stevens has shown.
In 2010, Stevens published a review of breast cancer sensitivity in 164 countries, and found a 30 to 50 per cent increased risk of cancer in nations with the worst light pollution, but no increased prevalence of non-hormonally dependent cancers in the same populations.
As we discussed a litany of light-related problems, I asked Stevens: ‘Is it a legitimate question to ask if light is the major factor in depression, obesity, and cancer? Is there potential for light to be the reason behind all of those things?’
‘Yes,’ he said flatly. ‘No doubt about it.’
The day is coming when doctors might feel confident saying so, he added, just as they now say that smoking causes lung cancer. The murky part is what to do about it.