Taking your e-reader to bed can disturb your sleep pattern, US doctors have warned, and waking up tired can lead to depression.
A team from Harvard Medical School compared reading paper books and light-emitting e-readers before sleep and found it took longer to nod off with a back-lit e-reader, which led to poorer quality sleep and being more tired the next morning. 
Original Kindle readers do not emit light so should be fine, say experts.
But there has been growing concern about the dangers of light before bedtime, the BBC reported.
In the US study, 12 people were locked in a sleep laboratory for two weeks and spent five days reading from a paperback and five days from an iPad.
Regular blood samples showed the production of the sleep hormone melatonin was reduced by reading an e-book.
People also took longer to fall asleep, had less deep sleep and were more tired the next morning.
The researchers said other e-readers such as the Nook and Kindle Fire produced similar wavelengths of light and would have the same impact.
The findings were published in the journal Proceedings of the National Academy of Sciences.
With tiredness often leading to depression, a usually successful treatment for this is available from the more than 1,800 members of the National Council for Hypnotherapy (NCH) who are qualified and spread across the UK.
Time spent in hypnosis with a professional hypnotherapist has been proved to help. Hypnotherapists look at people as a whole, rather than just treating symptoms. Hypnotherapy for depression works with both the conscious and the subconscious mind in order to help the desired results.
Referring to the US study, Dr Victoria Revell, who researches the impact of light on the body at the University of Surrey, told the BBC: “This is a very good study and I think it’s really interesting. We should be advising people to minimise their light-emitting e-reader use in the evening, particularly teenagers who are a group that are using their phones and tablets late in to the evening.”
Teenagers naturally have a late body clock, which makes them slow to rise in the morning and up late at night.
“People who already have a delayed body clock are delaying themselves much further and that is a very important message,” Revell added.
Lead US researcher Prof Charles Czeisler told the BBC News website: “The light emitted by most e-readers is shining directly into the eyes of the reader, whereas from a printed book or the original Kindle, the reader is only exposed to reflected light from the pages of the book.”
He said disrupting sleep in turn affected health.
“Sleep deficiency has been shown to increase the risk of cardiovascular disease, metabolic diseases like obesity and diabetes, and cancer. Thus, the melatonin suppression that we saw in this study among participants when they were reading from the light-emitting e-reader concerns us.”
Our bodies are kept in tune with the rhythm of day and night by an internal body clock, which uses light to tell the time.
But blue light, the wavelength common in smartphones, tablets and LED lighting, is able to disrupt the body clock. Blue light in the evening can slow or prevent the production of the sleep hormone melatonin.
Depression, also known as major depression, clinical depression or major depressive disorder, is a medical illness that causes a constant feeling of sadness and lack of interest. Depression affects how the person feels, behaves and thinks. Hypnotherapy may help identify the causes and origins of the depression. Once this occurs people often describe it as a ‘light going on’.
Hypnotherapy can also help the sufferer recognise any patterns of negative thinking they may be caught up in.
If your sleep patterns are disrupted and leading to tiredness, irritability and feeling down, locate an NCH hypnotherapist near you by using their directory.
After sessions with a hypnotherapist you may feel more confident and more relaxed. Many people say that they are calmer and that they have more clarity of thought – able to make decisions more easily.
