Using data from a French cohort of children, a team of researchers shows that too little or too much nighttime sleep at age 2 is associated with an increased risk of wearing glasses at age 5. Their study thus establishes an early link between sleep and vision.

Sleep:, an, adapted, quantity, from, the, youngest, age, would, protect, vision

From an early age, it is possible to follow some good habits to preserve your vision. In particular a good use of screens, wearing sunglasses or a diet rich in vitamins and omega-3. A new study conducted by Inserm* researchers shows that good sleep hygiene is also important, and not the least. The researchers worked with the EDEN cohort, composed of children followed from their mother's last trimester of pregnancy until the age of 5 (even up to 10 years for some of them), and whose objective is to determine the factors that have an impact during childhood that may influence health in adulthood.

In the journal Scientific Reports, the researchers explain that they were interested in this specific topic because the prevalence of myopia is rapidly increasing worldwide. Estimated at 25% of the population, it could reach 50% by 2050, with its share of complications: learning or work difficulties, headaches, constraints related to wearing glasses... ". Knowing the causes of this trend would make it possible to set up preventive actions to try to reverse it. It has been shown in animals, in this case chicks, that the disruption of the circadian rhythm (which regulates the functioning of the body on a 24-hour cycle) leads to vision disorders. ", they note.

A cumulative effect of sleep and screen time

This disturbance was caused by the abnormal exposure of animals to light, considered as one of the most powerful (de)regulators of the circadian rhythm. The mechanism is already known: captured by the retina, a prolonged emission of light delays sleep and alters the sleep rhythm. This is why the researchers hypothesized that sleep disorders may be associated with vision problems in children. To test this possibility, they used data from 1130 children in the Eden cohort, including their sleep habits at age 2 and the quality of their vision at age 5 (wearing glasses for nearsightedness, farsightedness, other vision problems).

In this cohort, 20% of the 5-year-olds wore glasses and the analysis showed a U-shaped association between sleep and vision: children who slept little at age 2 were more likely to have glasses at age 5, as were those who slept a lot. While the average sleep duration is 11 hours and 5 minutes at the age of 2 years, those who slept less than 10 hours and 45 minutes had, at 5 years, an additional risk of wearing glasses of 43%. For the third of children who slept the most, this risk was 49%. A similar result was also observed in those who went to bed late at age 2 (average bedtime was 8:36 pm). 

The importance of quality and quantity of sleep until adolescence

According to the team, "these associations remain significant even when controlling for factors that may influence the results, in particular screen time, a known risk factor for myopia." At age 5, this "screen time" averaged 1 hour and 24 minutes per day in the cohort, and the risk of wearing glasses increased by 23% per hour of screen time, independent of sleep duration. Furthermore, the risk associated with sleep duration and that associated with screen exposure were cumulative: children who slept little or a lot at age 2 and were exposed to 1 hour and 24 minutes of screen time per day at age 5 were twice as likely to wear glasses as those who slept normally at age 2 and were not exposed to screens.

"Previously published studies on the vision of older children show a link between myopia and time spent indoors, especially under artificial light, studying, reading, watching screens... Our work indicates that a vision problem could appear much earlier, in connection with an inadequate amount of sleep at the age of 2 years. Our work indicates that a vision disorder could appear much earlier, in connection with an inadequate amount of sleep at the age of 2 years," explains Sabine Plancoulaine who led the study. "It is not excluded that the influence of sleep on vision extends into adolescence, at which stage the eye stops developing. "For the researchers, this result pleads for an adapted and quality sleep from the youngest age. And this "knowing that children will also benefit for their psychological or metabolic health. "concludes Sabine Plancoulaine.

*Researchers at the Centre for Research in Epidemiology and Statistics (CRESS, Paris)