Bright light, bright mind: Do kids need daylight to learn and thrive?


Sunlight is crucial if you're a plant. But even if you don't photosynthesize, exposure to daylight has a major impact on your health and well-being. This is true for children as well as adults. In fact, natural rhythms of daylight and darkness may be especially important during childhood.

It helps ensure kids develop healthy circadian rhythms. Studies indicate that many kids have trouble falling asleep at their appointed bedtime because their brain chemistry is out of sync: They get too little daylight during the day, and too much artificial light at night.

In addition, kids who don't get enough sunlight develop vitamin D insufficiency, which puts them at increased risk for certain health problems. These may include poor bone health (Borg et al 2018), cardiovascular disease (El-Fakhri et al 2014), and reduced muscle function (Carson et al 2015; Hazel et al 2012). There is also evidence that low vitamin D status could be a trigger for early puberty in girls (Chew and Harris 2013).

But what about mental performance? Certainly, poor sleep can contribute to attention and concentration problems -- problems that interfere with academic achievement. Moreover, experiments support the idea that bright morning light boosts mood (Leichtfried et al 2015; Gabel et al 2013; Te Kulve et al 2017), which could have an effect on motivation at school.

And now recent experiments on rats suggest an additional possibility: Maybe bright, daytime light has an effect on learning. Maybe it alters the brain. Take that daylight away -- keep individuals indoors, in dimly-lit rooms -- and they might suffer learning deficits.

The experiments were performed on nile grass rats -- a species that sleeps at night and remains active during the day, just as humans do. From the beginning of the study, all rats were kept on strict schedules of 12 hours of constant lighting followed by 12 hours of darkness. But the intensity of daytime light varied (Soler et al 2018).

  • For rats assigned to the bright light group, daytime meant light levels of 1,000 lux -- roughly what we experience outdoors on an overcast day at noon.
  • For rats assigned to the dim light group, daytime meant light levels of 50 lux -- close to the levels that light bulb manufacturers recommended for a living room.

The rats stayed on these schedules for 4 weeks, at which point they were introduced to a problem-solving challenge called the Morris Water Maze. During this challenge, each rat was placed in a pool of water. The water was made opaque by nontoxic, white paint, which concealed the existence of a resting platform just under the water's surface.

Rats had to swim until they discovered the resting platform -- something they were highly motivated to find. A steep wall surrounded the sides of the pool, and the wall was marked with a variety of distinctive shapes and designs.

Once a rat found the platform, it therefore had the opportunity to use the nearby designs as landmarks. If a rat remembered the landmarks, it would be able to quickly find the platform the next time it was placed in the pool.

The question was: How readily would rats learn?

All of the rats had the same opportunities. They were placed in the pool twice each day for 5 days running. And all of the rats showed signs of learning -- they made their way to the hidden platform more quickly as the days went by.

But during each morning session, the rats housed under dim light "living room" conditions performed worse than the "bright light" rats -- as if they had forgotten more overnight.

And when the researchers gave the rats a longer break -- 24 hours between challenges -- the dim light "living room" rats showed a pronounced learning deficit.

Whereas the "bright light" rats had no trouble zeroing in on the location of the platform, the rats living with dim light schedules floundered. They were no more likely to swim in the correct location than you would expect by chance.

The results weren't caused by differences in lighting during swim sessions, because all rats experienced the same lighting conditions (about 300 lux) when they were in the Morris Water Maze. And interestingly, the behavior outcomes were accompanied by visible differences in brain tissue.

When researchers looked in the hippocampus (a part of the brain associated with spatial learning), they found that the "dim light" rats had lower levels of brain-derived neurotrophic factor, or BDNF -- the substance that promotes the growth of new brain cells.

In addition, neurons in the hippocampus were physically different. The neurons of the "bright light" rats had more spines on their dendrites -- evidence that these neurons had grown stronger synapses, a hallmark of learning. 

Finally, the researchers found they could change the brains of "dim light" rats by transferring them to the bright light condition. After four weeks, they too experienced increased BDNF and grew more dendritic spines (Soler et al 2018).

What should we make of this? We can't assume that humans would respond the same way. This is a single study that needs to be replicated, and we need studies that include human subjects.

However, our basic physiology has a lot in common with these rats, so I think it would be equally foolish to assume this research has no applications to humans.

And given all the other good reasons we have to expose our children to plentiful daylight, we have nothing to lose by making an extra effort to ensure that every child gets his or her time in the sun.

Yes, we need to take precautions against harmful UVB rays. Sunscreen and hats are important protections when sunlight is intense. But we shouldn't regard sunlight as a troublesome health threat on the one hand, or a luxurious perk on the other. Kids need daylight for their health and well-being.

More reading

Kids need daylight, but it isn't just the light that's good. Research suggests that being outdoors -- in nature -- is intrinsically beneficial. More more information, see this article. In addition, read more about BDNF and the cognitive effects of exercise.

References: Bright light, bright mind: Why kids need daylight to learn and thrive

Barkmann C, Wessolowski N, Schulte-Markwort M. 2012. Applicability and efficacy of variable light in schools. Physiol Behav. 105(3):621-7.

Borg SA, Buckley H, Owen R, Marin AC, Lu Y, Eyles D, Lacroix D, Reilly GC, Skerry TM, Bishop NJ. 2018. Early life vitamin D depletion alters the postnatal response to skeletal loading in growing and mature bone. PLoS One. 13(1):e0190675.

Carson EL, Pourshahidi LK, Hill TR, Cashman KD, Strain JJ, Boreham CA, Mulhern MS1. Vitamin D, Muscle Function, and Cardiorespiratory Fitness in Adolescents From the Young Hearts Study. J Clin Endocrinol Metab. 100(12):4621-8.

Chew A, Harris SS. 2013. Does vitamin D affect timing of menarche? Nutr Rev. 71(3):189-93.

El-Fakhri N, McDevitt H, Shaikh MG, Halsey C, Ahmed SF. 2014. Vitamin D and its effects on glucose homeostasis, cardiovascular function and immune function. Horm Res Paediatr. 81(6):363-78.

Gabel V, Maire M, Reichert CF, Chellappa SL, Schmidt C, Hommes V, Viola AU, Cajochen C. 2013. Effects of artificial dawn and morning blue light on daytime cognitive performance, well-being, cortisol and melatonin levels. Chronobiol Int. 30(8):988-97.

Hazell TJ, DeGuire JR, Weiler HA. 2012. Vitamin D: an overview of its role in skeletal muscle physiology in children and adolescents. Nutr Rev. 70(9):520-33.

Leichtfried V, Mair-Raggautz M, Schaeffer V, Hammerer-Lercher A, Mair G, Bartenbach 4, Canazei M, Schobersberger W. 2015. Intense illumination in the morning hours improved mood and alertness but not mental performance. Appl Ergon. 46 Pt A:54-9.

Soler JE, Robison AJ, Núñez AA, Yan L. 2018. Light modulates hippocampal function and spatial learning in a diurnal rodent species: A study using male nile grass rat (Arvicanthis niloticus). Hippocampus. 28(3):189-200.

Te Kulve M, Schlangen LJM, Schellen L, Frijns AJH, van Marken Lichtenbelt WD. 2017. The impact of morning light intensity and environmental temperature on body temperatures and alertness. Physiol Behav. 175:72-81.

Image credit for "kids need daylight':

Title image of happy toddler in sunlight and smoke by Graham Crumb / flickr

Child in sunlit forest by Philippe Put / flickr