Medical: Why your children should be playing outside

"Go outside and play" may be a parental refrain heard more often during school holidays, but it's also proving to be a prescription for better health on a number of fronts.

One new analysis of recent eye studies among children and teens found that time spent outdoors is related to a reduced risk for nearsightedness.

British researchers speaking at the journal Ophthalmology's meeting in Orlando, Fla., last fall reported that for each additional hour a week spent outdoors, the risk of developing nearsightedness dropped about 2 percent.

The eight studies merged into the analysis included more than 10,000 subjects and showed that nearsighted kids spent an average of 3.7 fewer hours a week outdoors than did those with normal or farsighted vision.

The analysis suggests that more exposure to natural light and time spent looking at more distant objects may be key factors, rather than doing or not doing any particular thing. Two of the studies that tried to assess effects from watching TV or playing video games didn't show any connection.

But another study reported by Australian researchers last spring found a very strong effect on the arteries at the back of the eyes in 6-year-olds who spent the most time "on screen" with television, computers or video games.

By contrast, kids who regularly participated in outdoor physical activity had retinal arteries an average of 2.2 microns wider than children with the lowest levels of such activity. A micron is one-thousandth of a millimeter, or one-25th of a thousandth of an inch.

Narrowing of the retinal arteries is considered a marker for future cardiovascular risk. The researchers found that the magnitude of narrowing associated with each hour of screen time was similar to a 10-millimeter increase in systolic (beating heart) blood pressure in children.

The study of nearly 1,500 children included both questioning them and their parents about their activities, taking vital signs and taking digital photos of the blood vessels behind the eye.

The children spent an average of just under two hours a day in screen time, and about 36 minutes a day in physical activity. But the most active, with the widest arteries, were active for just over an hour a day; those with the narrowest arteries were active for under a half hour.

Researchers have also discovered that certain regions of the brain linked to addiction experience increased blood flow when people who are considered dependent on tanning are exposed to ultraviolet light.

And it's well known that too much or too little light exposure can affect mood, depression and production of various hormones as well as vitamin D levels. A number of studies have tied sun exposure to various increased or decreased risk for human papilloma virus, multiple sclerosis and fungal infections.

Among the more recent claims, by British researchers, is that exposing the virus that causes chickenpox to ultraviolet rays in sunlight makes it less likely to spread to other people.

They note that both chickenpox and its nastier adult cousin, shingles, are less common in the tropics and that outbreaks of the disease in temperate zones tend to come in the winter season when UV rays are weakest.

(Contact Lee Bowman at bowmanl(at)shns.com. For other columns, visit www.scrippsnews.com.)