Can a blind person still benefit from the positive effects of natural light on circadian rhythms and mental well-being? I lost my remaining light perception 10 years ago and since that time I’ve had insomnia. This would suggest that the answer to my question is no, but maybe I just need to get out more.
Linda Geddes, author of Chasing the Sun, Bristol, UK
The reader may have non-24-hour sleep-wake disorder, which is common in people who have no light perception whatsoever.
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In every cell of our body, there are molecular clocks that regulate the timing of pretty much every physiological process, from the release of hormones to the activity of immune cells. These clocks run on roughly 24-hour schedules, though some people are closer to 23 hours, others more like 25.
The way we stay synchronised to the 24-hour day is through signals from light-sensitive cells at the back of the eye called intrinsically photoreceptive retinal ganglion cells. When light hits those cells each morning, it acts like the reset button on a stopwatch: the brain adjusts its timing, then signals to the body’s molecular clocks to do the same.
In some people who are blind, those cells are damaged, and this connection is broken. As a result, they revert to their genetically determined timekeeping. People with a 23-hour clock would wake at 8 am one morning, 7 am the next, then 6 am and so on. Because of this, they often experience insomnia. It is worth seeking advice from a certified sleep consultant, as melatonin supplements can be an effective treatment, if diagnosed.
People who are blind still benefit from sunshine to make vitamin D. There is also mounting evidence that sun exposure tweaks our immune cell activity and blood pressure, which could benefit our health.
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