When psychiatrist Norman Rosenthal moved from South Africa to the US in the 70s, something changed. In the colder winters of New York he and his wife felt their energy levels slump and their mood drop. So when he met fellow scientist Alfred Lewy at a party, it was easy for the pair to begin chatting about Lewy’s research into melatonin, a hormone associated with sleep – and how light and mood might be entwined. Which is how, more than 30 years ago, the pair became the first scientists to describe seasonal affective disorder – and treat it with light therapy. Since then our understanding of the way light affects us, Rosenthal tells me, has “skyrocketed”.
Sad, which is characterised by cognitive problems, withdrawing from friends and family, weight gain and increased time spent sleeping, may affect one in 20 people in the UK to a disabling degree. But as many as one in five can suffer the effects of less severe “winter blues”, struggling through darker days being less productive and happy than normal.
“Sad helped us recognise that light and dark are strong influences of mood and behaviour and many of us don’t get enough light,” says Rosenthal. “But now we know a large percentage of the population has some lack of functionality in the winter.”
His work opened up new fields for exploration. For instance, it is now understood that light therapy – using light boxes to mimic the effects of the sun’s rays – can help people with forms of depression that are not seasonal. It’s useful for patients for whom medication is a tricky option, such as pregnant women and the elderly.
Light’s mood-enhancing effect can be used in other ways too, says Rosenthal, now clinical professor of psychiatry at Georgetown University school of medicine. “The most cutting edge is with people who have had cancer and are having chemotherapy. They are now getting light and it helps them feel better.”
Light, he explains, has an effect on our serotonin levels, a hormone that can affect our mood and energy. “In Australia there was a study where they measured and evaluated the factors that make serotonin concentration levels go up and down. One of the most important factors was light.”
Then there is the research into the effect of light on our natural body clocks. “It can shift it earlier or later,” says Rosenthal. “Brighter light is more potent in this.” He thinks research in this field will be the next discovery on the horizon. “I think we will find out a bit more about the biological pathways associated with Sad. What genes does light turn on and off?
“They have discovered clock genes [in mice] which regulate their biological clocks. When they disrupt them in animals it disturbs their rhythms and behaviours. This may lead us to understand how variations in our genes may influence the way we respond to light.”
But he also sounds a cautionary note. “Light can help people in so many ways, but it is not a cure-all and it can be harmful. There is an association between light pollution and cancers. Breast cancer and other cancers are associated with areas where there is a lot of light outside – street lights for instance.”
This could be, he says, because darkness allows melatonin to be secreted, which “has been hypothesised to help prevent cancer”.
Rosenthal says there have also been leaps in the way Sad is treated – from the different intensities of light, to the time of day that light has the most effect on our bodies (the morning). Cognitive behavioural therapy can be helpful too, he says, though not everyone is keeping up – the National Institute for Health and Care Excellence (Nice) has steadfastly refused to offer lightboxes on the NHS: “Frankly, I think that is ridiculous. Hundreds of thousands of people use light and depend on it. I think their position is very curious and hard to understand.”
Most recently, he has researched the effect of botox injections between the eyebrows to help with depression – and is now looking into whether this too, could have an effect on Sad sufferers. “It’s wild,” he says. Thirty years ago, “I didn’t realise how important [our work] would be. Now we have helped people live a full life, all year round.”
