Here Comes the Sun continued...
But before you grab the beach towel and head for the seashore, keep in mind that particularly in the higher northern latitudes, vitamin D levels can be problematic. If you live above 40 degrees north latitude -- north of Philadelphia, for example, or Denver -- you won't make much of any vitamin D in the winter.
A study at the University of Maine monitored vitamin D levels in 23 girls (ages 10-13, all residents of Bangor, Maine). In findings presented at the American Society for Bone and Mineral Research last September (2003), nearly half of these girls had insufficient levels of vitamin D in their blood in March, the time of year when levels tend to be lowest due to decreases in sunlight exposure during the winter.
"I was surprised by some of our findings," Sullivan tells WebMD. "These were healthy, active, light-skinned girls who spent a lot of time outdoors. They were eating well-balanced diets, and many were milk drinkers. So if anyone was going to have normal vitamin D status, you'd think it would be them. But their levels were quite low by March. We're in central Maine at about latitude 44 degrees north, and we don't make vitamin D in our skin for five months a year -- between November and March."
That kind of sun scarcity can take its toll on human health. "There is some striking evidence that as you go farther north, the incidence of certain kinds of cancer increases," says Sullivan. "There is more prostate and colon cancer in the north than in those who live closer to the equator."
The correlation is similar for multiple sclerosis. Research has shown the immune disorder is more common in areas with fewer hours of sunlight. For example, multiple sclerosis is more common in Canada and the northern states of the U.S. than in the southern states.
The Perils of Sun Worshiping
The sun isn't all good, of course. As any dermatologist will eagerly tell you, too much sun could risk a lot more than a bad sunburn. Routinely overdosing on sunshine could translate into life threatening skin cancer. On the other hand, if you're completely sun-phobic from sunrise to sunset, you may pay the price in the amount of vitamin D your body produces, cautions Holick, author of The UV Advantage.