The vitamin D window has closed

Me in the snow. Photo by Jackie Brewer.

Seven or eight years ago, I became aware of research that suggested that vitamin D deficiencies were a possible cause of seasonal depression. As I have long suffered (albeit mildly) from SAD, I figured it was worth trying a vitamin D supplement, and it did seem to help.

I worry just a bit about taking a supplement, because there are dangers with excessive doses of vitamin D. (A random site on the web suggests that doses over about 10,000 IU per day are dangerous, if continued for a period of months.)

So, I prefer to get my vitamin D via sunlight. A pale-skinned person like me can make upwards of 10,000 IU of vitamin D in just a few minutes of mid-day summer sun—but there’s no danger of getting an overdose: your skin keeps making it as long as you’re in the sun, but once saturated with an optimal amount, it starts un-making it as fast as it makes it.

But it’s the UVB light in the sun that makes the vitamin D, and at my latitude (I live at almost exactly 40° north), little or no UVB gets through the atmosphere during the winter. Specifically, the vitamin D window closed this year on November 20th. It’ll open again on January 20th—although of course it’ll be too cold to expose much skin to the sun for a month or two after that.

This past summer, I spent more time in the sun than in years past, and found that it made me feel especially good—like the opposite of seasonal depression. I imagine it’s the extra vitamin D, although I don’t see any way to tweeze evidence for that hypothesis out from the many other possible reasons. Perhaps it was just more bright light (as opposed to the UVB in particular)—surely the sun is the world’s best light box. Perhaps it was just being more active (I tend to get my sun walking or running, not sitting or lying in the sun). Perhaps it was the endocannabinoids produced during the longer runs in particular. Perhaps it was more time in nature (I spend a lot of my outdoor time walking or running in our local prairie and woods), which is known to be good for the mood. Perhaps it was the extra “together time” Jackie and I got on our very long walks. Perhaps it was the solitude of walks and runs by myself, providing space for meditation.

Whatever it was, I miss it in the winter, and I fixate on a vitamin D deficiency as a possible culprit. Maybe I’ll up my supplement dose. Of course, I won’t do just that. I’ll use my Happy Light™. I’ll go for long walks in the cold and snow. I’ll get out in the prairie and the woods. I’ll try to cover all the possibilities. But I’ll keep taking my vitamin D.