iPad use and depression link questioned
Using an iPad at night 'could trigger depression', The Daily Telegraph has reported in what appears to be a textbook example of health journalism cut-and-paste from a press release.
This news is loosely based on an animal study that aimed to investigate the effects of abnormal exposure to light on mice. Researchers compared a group of mice exposed to abnormal light patterns with a group of mice exposed to 'regular' light patterns and examined their behaviour through a range of tests.
They found that mice exposed to abnormal light patterns showed negative effects on their mood and cognitive function, as well as higher levels of stress hormones, which the researchers say are linked to depression.
Interestingly, the media has interpreted these findings as suggesting that using an iPad or laptop at night could lead to depression, which is an exaggeration and not what this study looked at.
While we can judge how well mice navigate a maze or measure their hormone levels, there is no way of telling if a mouse is depressed.
The spurious link between this study and an alleged connection between depression and night-time iPad and laptop use seems to be due to an article posted on Johns Hopkins University’s website. Reporters who covered this story appear to have only read this article, rather than the original research.
However, this study is valuable, as previous research has suggested that exposure to abnormal light patterns, such as those experienced by night shift workers, can have a negative impact on mental health.
But the media's extrapolation of the results from how mice behave during animal testing to humans using iPads at night is tenuous.
Where did the story come from?
The study was carried out by researchers from Johns Hopkins University and Rider University, USA. It was funded by the David and Lucile Packard Foundation grant. The paper was published in the peer-reviewed journal Nature.
Despite the link made to iPad use by the media in the headlines, this is not what the research investigated. Aside from the utterly misleading headlines, the main body of the reporting on the study was covered appropriately in both The Daily Telegraph and the Daily Mail. Both newspapers pointed out that the research was carried out in mice.
The term 'iPad' is one of the most searched for terms on the internet. A story containing the term will therefore rank highly on search engines. This technique is known as search engine optimisation, or SEO. The story also taps into fears about new technology that have been around since Luddite cotton workers started breaking their looms in the 17th century. These fears are easily preyed on by linking everyday objects with perceived risk.
A recent example of this is the unproven link between mobile phones and cancer.
What kind of research was this?
This was a laboratory-based animal study that investigated whether irregular light directly affected the mood and cognitive functioning of mice.
It is often difficult to interpret the results of animal research and caution should always be exercised when trying to generalise the findings to humans.
What did the research involve?
The researchers used a group of mice that were initially exposed to 12 hours of light and 12 hours of darkness.
Following this, some of the mice were then exposed to an abnormal light-dark cycle of three-and-a-half hours of light and three-and-a-half hours of dark for two weeks, with another group remaining on the initial longer light-dark cycle of 12 hours.
The researchers state that sleep deprivation and disrupted circadian rhythms (the body's normal biological cycles) underlie mood and cognitive disorders.
They report that in order to specifically look at the effect of light exposure, the mice's normal sleep patterns mice were not disrupted. This ensured that the mice experienced normal sleep patterns and circadian rhythms.
The intensity of light was also chosen to cause no disruption to the mice's normal body rhythms and was not intense enough to disrupt biological functions such as metabolism.
After two weeks the mice underwent a series of behavioural tests to assess their depression-like behaviour. Mice that underwent the shorter light-dark cycle (three-and-a-half-hour cycles) were compared with mice that had normal 12-hour cycles), who acted as controls. The behavioural tests carried out by the researchers included:
- A sugar preference test over two days, where mice were given the option of consuming water only or water containing sucrose. Researchers considered that a decreased preference for sugar showed an increase in depression-like symptoms.
- A forced swim test in a container of water for six minutes, where more time spent immobile during the last four minutes of testing was considered to show increased depression-like behaviour.
A lack of interest in novel experiences and physical apathy are often signs of a depressed mood in humans.
The researchers then looked at whether exposure to abnormal light patterns had an effect on learning difficulties in the mice. This was assessed by a water maze scenario, where the time spent and the distance travelled between start and finish were used as indications of anxiety-like behaviour, as well as an object recognition test. The researchers also gave antidepressants to the mice they thought had displayed depression-like symptoms and assessed their response.
What were the basic results?
The main results of this animal study were:
- mice exposed to the abnormal light-dark pattern (three-and-a-half-hour cycles for two weeks) had higher levels of coricosterone (a stress hormone linked to the circadian pattern of sleep and depression) compared with mice exposed to the longer light-dark cycle (12-hour cycles)
- mice that were exposed to the shorter light-dark cycle had a decreased preference for sugar compared with mice that were exposed to the longer light-dark cycle
- mice exposed to the shorter light-dark cycle spent significantly more time immobile in the forced swim test than the control mice
- mice given antidepressants after showing learning deficits caused by the abnormal light-dark cycle had their learning abilities restored
Lead researcher Professor Samer Hattar of Johns Hopkins University is quoted as saying: "Of course, you can't ask mice how they feel, but we did see an increase in depression-like behaviours, including a lack of interest in sugar or pleasure seeking, and the study mice moved around far less during some of the tests we did. They also clearly did not learn as quickly or remember tasks as well. They were not as interested in novel objects as were mice on a regular light-darkness cycle schedule."
How did the researchers interpret the results?
The researchers concluded that mice exposed to an abnormal light cycle showed increased depression-like behaviours and lower cognitive function. They say their findings demonstrate the ability of light to influence cognitive and mood functions directly through intrinsically photosensitive retinal ganglion cells.
These cells act much like the light-sensitive semiconductors found in digital cameras. They take a snapshot of light in the same way as the retina, which is then converted into digital information and sent to an internal computer (or the brain) and assembled into a visual image. While retinal ganglion cells are primarily responsible for vision, there has been speculation that they can also have an effect on cognition and mood.
In discussing the research findings, Professor Hattar said: "Basically, what we found is that chronic exposure to bright light – even the kind of light you experience in your own living room at home or in the workplace at night if you are a shift worker – elevates levels of a certain stress hormone in the body, which results in depression and lowers cognitive function."
Conclusion
Few conclusions about the effect of light patterns in humans can be drawn from this animal study. Certainly, no conclusions can be drawn about whether using iPads or other tablet computers at night causes depression-like symptoms.
Despite the research finding that mice displayed depression-like symptoms following exposure to abnormal light patterns, the findings may not translate to humans, where depression can be more accurately diagnosed. To draw firmer conclusions further research carried out in humans is needed.
Consequently, the headline that 'using an iPad at night could trigger depression' seems like an extraordinary leap of the imagination and is not a claim that can be supported by this animal study.
However, staying up all night using an iPad or laptop on a regular basis could make you sleep-deprived. Disturbed sleep patterns and reduced sleep may well impact upon your mood, concentration and behaviour.
