Why staying outside could be good for you

IN THIS digital age where playtime has grown almost synonymous to gadget time, children spend more of their waking hours indoor, tinkering with electronic game consoles or browsing on the computer. Playing in the sun with other children has significantly lost its appeal. 

This could change again as more studies underscore the benefits of outdoor time. More people are realising that mothers’ remark to “Go out and play” accentuates the value of outdoor activities not only in promoting socialisation skills amongst children, but also, and more importantly, in improving their health, in particular eye health.

Scientific and anecdotal evidence have long supported the “outdoor effect” on nearsightedness or myopia, an eye condition that causes distant objects to appear blurry. Studies have signified that spending more quality time outside reduces the risk of nearsightedness in kids, even amongst those who use up a lot of their time squinting at electronic devices or reading.

In Asia, which is amongst the regions with the highest number of myopia cases, some nations have raised the amount of time every day that children are exposed outdoor in efforts to minimise the need for glasses. This is despite the absence of definitive data on exactly how outdoor time protects the eye from myopia.

Donald Mutti, OD, PhD, optometrist at The Ohio State University College of Optometry admits experts do not know exactly how outdoor time affects the eyes. “If we knew, we could change how we approach myopia,” he said.
Nevertheless, the specialist said that existing data suggest spending more than 14 hours a week outdoors results in a three-fold drop in the chances of a child genetically predisposed to myopia to acquire the condition.
Dr Mutti plans to use a pilot grant from Ohio State’s Center for Clinical and Translational Science (CCTS) to conduct further studies. Specifically, he hopes to focus on variables that he thinks have the most potential effect on myopia. These are invisible ultraviolet B rays (UVB) and vitamin D, and visible bright light and dopamine.

According to Dr Mutti, the eyes of children aged between five and nine are still developing. Nearsighted could be linked to changes during this growth period, which can cause the distance between the lens and retina to lengthen, a factor in developing myopia. He said the different types of outdoor light may help preserve the proper shape and length of the eye during this stage.

Vitamins for good vision
Studies, including one by Dr Mutti, have shown that nearsighted people have lower vitamin D levels in their blood, pointing to the negative effects on the eye of less time spent outdoors.  
Vitamin D, which is produced with the help of UVB light, supports the smooth muscle tissue found around the lens of the eye. In addition to helping focus light on the retina, this muscle assists in maintaining the proper eye shape and the length between the lens and the retina during the eye’s growth stage. 

The difficulty in measuring vitamin D levels, however, posits a problem for data interpretation. For one, studies should take into consideration that vitamin D levels change markedly from season to season. Vitamin D levels spike during fall even if people usually get the biggest UVB exposure during summer. 

“We don’t know if vitamin D is simply a proxy for measuring outdoor time, or if it is actually exerting a biological effect on how the eye works and develops,” said Dr Mutti.

Amongst his research objectives is to develop a protocol for measuring vitamin D levels. One of his studies uses monitors worn by participants to detect UV and visible light exposure. Vitamin D levels are also measured using blood and saliva samples. It is hoped that the study will validate the way vitamin D is measured. This will then help experts understand in a more accurate way the role it plays in large-scale studies, Dr Mutti added.

Another vitamin affecting eyesight that scientists are exploring more extensively is vitamin A.

A study published in the journal Nature Chemical Biology discusses the success of researchers at Case Western Reserve University School of Medicine in uncovering the mechanism by which the enzyme Lecithin retinol acyltransferase (LRAT) stores vitamin A, a process that is indispensable for vision.

LRAT helps convert vitamin A to a usable form called retinyl ester, which then regulates the cellular uptake of the vitamin and is therefore essential for our eyes to function. The lack of LRAT causes vitamin A deficiency and blindness.
According to Marcin Golczak, one of the authors and assistant professor of pharmacology at Case Western Reserve, the findings will help experts understand the molecular mechanisms of blindness caused by mutations in the enzyme. The data can be used in designing small molecule therapies for degenerative eye diseases. Methods to transport small molecule drugs to the eye can adopt the LRAT’s enzymatic activity allowing specific cells to absorb vitamin A. Once these drugs accumulate in the eye tissue, the effective dose can be decreased to minimise the risk of systemic side effects.

The researchers also studied how LRAT is different from the rest of its protein family. Dr Golczak, medical student Avery E. Sears, pharmacology instructor Philip D. Kiser, and pharmacology chair Krzysztof Palczewski compared LRAT with related enzymes belonging to the N1pC/P60 family. The analysis revealed that the substrate specificity, or the substances on which the enzymes act, are determined by small variations in the protein sequences. These also govern the physiological functions of these enzymes.

LRAT’s close relative HRAS-like tumor suppressor 3, also known as HRASLS3, does not process vitamin A but helps regulate the breakdown of triglycerides in white fat cells. Excess accumulation of triglycerides, which provide body tissues with an energy source, leads to obesity and related metabolic syndrome, subsequently raising the risks of heart disease, diabetes, and other health problems.

According to Dr Golczak, “Evolution of enzymatic activities via gene duplication, mutation and selection has led to the present diversity of metabolic capabilities. Our studies explain what modification in the cellular enzymatic machinery enables vertebrates to efficiently take up and store excess vitamin A.”

Whilst LRAT and HRASLS3 have a common molecular structure, LRAT has an insertion of 11 amino acids followed by a conserved 19 amino acid stretch not found in HRASLS. Replacing the 30-amino-acid sequence in HRASLS3 and its two closest relatives, HRASLS2 and HRASLS4, with the sequence from LRAT reveals that unmodified HRASLS proteins failed to catalyse the conversion of vitamin A into retinyl ester. Modified HRASLS proteins, however, robustly produced retinyl ester.

These further show that the replacement caused major structural rearrangements, including interactions between two protein molecules and domain swapping between neighbouring subunits. The alteration in the active site architecture, protein/lipid membrane interactions, and promotion of binding to a different substrate, in this case, to vitamin A, helped foster the new enzymatic activity.  

Visible bright light and the eye
Besides vitamin D, sunlight helps prevent myopia through exposure to visible light. Visible light outdoors, which is at least 10 times brighter than indoor lighting even on a cloudy day, help specialised cells in the retina control the size of the pupil’s dilation to let more or less light in. Another function of these specialised cells is connecting to other cells that release dopamine, an important neurotransmitter in the eye and brain. Dopamine has been shown to slow down the growth of the eye. However, directly measuring dopamine release in the eye is currently not feasible because of the lack of technology.

Dr Mutti plans to use a procedure developed by Andrew Hartwick, OD, PhD, through another CCTS-funded research in measuring dopamine release. This procedure, which was meant for the early detection of glaucoma, studies the pupil’s reaction to light.

According to Dr Mutti, “Dr Hartwick has developed a protocol that measures how much these specialised retinal cells contribute to pupil responses to blue and red light. Our initial research suggests that the pupil responds more if these cells have been exposed to a lot of sunlight in the previous few days. That could serve as a proxy for how much dopamine the eye has been producing."

Dr Mutti and his team plan to use study results, which have been presented to the American Academy of Optometry annual meeting, plus other ongoing researches to develop methodologies for large-scale clinical trials. A more definitive knowledge of how the outdoor effect prevents myopia could help more people avoid a lifetime of depending on eyeglasses. In the meantime, Dr Mutti reminds parents not to forget sunglasses and sunscreen as they prod their children to go out and play.