Depression affects more than 300 million people worldwide, and while antidepressant medications help many patients, nearly one in two people do not respond to the first medication they try.
New research led by Flinders University suggests that the key to more effective treatment may lie in understanding how light affects individuals' sleep and internal 'body clock'.
"Light does something even more profound than help us see. It sets our internal biological clock, regulates our sleep-wake cycles, and directly influences our mood and wellbeing," says Matthew Flinders Professor Sean Cain, who is leading a new study looking to recruit participants to the Illuminate Study and expand the research.
"Our eyes contain specialised cells that detect light and send signals directly to the brain's master clock, as well as other brain areas which regulate our mood and thinking.
"This system evolved to respond to the very bright days and dark nights provided by the rise and fall of the sun. However, modern life has blurred this natural distinction
"We spend most of our time indoors under artificial lighting that is dim during the day and relatively bright at night - the opposite of what our biology expects," says Professor Cain from FHMRI Sleep Health, College of Medicine and Public Health.
To further investigate and explore new treatments, the Flinders University team has launched the Illuminate Study to examine how light sensitivity changes during depression and antidepressant treatment.
People aged 18-35 with current depression are invited to undergo detailed assessments of their circadian function, including brain imaging, pupillary assessments, sleep recordings and measures of hormone patterns in the laboratory, as well as at-home monitoring of light exposure and sleep in daily life.
Participants will then begin treatment with the commonly prescribed antidepressant, citalopram, and monitored for approximately eight weeks.
After this treatment period, all assessments will be repeated to see how light sensitivity has changed and whether these changes relate to treatment response.
This study will be the first to examine how the function of the body clock changes across antidepressant treatment within the same person.
"By understanding who responds best to treatment and why, we can move toward more personalised approaches to depression treatment," says Professor Cain, from the College of Medicine and Public Health.
Participants receive an individualised report of their light sensitivity, sleep and light patterns, and can receive up to $2,000 compensation upon completion of the study.
More background: Led by Professor Cain, Monash University and other experts, a previous study of more than 400,000 people found that each additional hour spent in outdoor light during the day was associated with lower odds of depression and greater happiness. Time outdoors was also linked to better sleep, less tiredness, and easier mornings.
Professor Cain says his research demonstrates that everyone responds to light in a slightly different way.
"Our research shows that people currently experiencing depression have a lower level of sensitivity to light; their biological clocks don't respond as strongly to light cues as they should," says Professor Cain.
"This reduced light sensitivity may explain why the biological clock becomes misaligned in depression.
"If your body clock can't properly detect the light-dark cycle, it can drift out of sync with your daily activities, leading to the sleep and mood disturbances seen in depression."
Interestingly, Professor Cain adds that the most common antidepressants (selective serotonin re-uptake inhibitors; SSRIs) appear to increase the sensitivity of the biological clock to light. This could be one mechanism by which these medications work.
Studies have shown that combining SSRIs with bright light therapy produces better outcomes than either treatment alone, suggesting that boosting the body clock's response to light may be a key therapeutic target.
In another recent study, a landmark study of over 85,000 people published in Nature Mental Health revealed how important this light-dark pattern is for mental health. The researchers found that greater exposure to light at night was associated with a 30% increased risk of depression. Additionally, brighter daytime light exposure was associated with a 25% reduced risk of depression.
The effects were independent of one another, meaning both day and night light patterns are important for mental health.
