Me and my shadow: Is your sunshine the “right” sunshine for vitamin D production?

We produce vitamin D from sunlight exposure, but not all sunshine is created equal.

Only a narrow spectrum of sunlight ultraviolet radiation (UV) stimulates our body’s production of vitamin D, and it’s most intense at the equator where the sun is directly overhead. However, as you move away from the equator, UV radiation varies by season, being the most intense in the summer when the sun is high in the sky. In northern areas, the slant of the sun is such that during the winter months we produce virtually no vitamin D.

ShadowAs getting vitamin D from the sun is so important, I am delighted to share with you a very simple system for estimating the Vitamin D–generating potential of your sunlight. It comes from Canadian vitamin D authority, Dr. Reinhold Vieth, who reports that all you need to do is to look at your shadow. If your shadow is shorter than you are, then you are able to produce vitamin D from this sunlight. If your shadow is longer than you are then you know you are not being exposed to that small spectrum ultraviolet radiation that allows for vitamin D production.

I tried the simple system myself here in Syracuse, New York, in mid-July:
–    At 7 AM, my shadow was much taller than I am,
–    by 11:30 AM, with the sun reaching directly overhead, it was very short,
–    by 1:30 PM, it was even shorter,
–    by 3:30 PM, the shadow was still shorter than I, but growing….
–    and by 4 PM, me and my shadow were about the same size.
From past research we know that these hours around midday are indeed the prime time for vitamin D production. Actually this little tidbit is but one part of a very impressive vitamin D lecture Dr. Vieth recently presented at a conference in London. For a YouTube video of this lecture I refer you to

Oh yeah, be sure to pick a sunny day for this experiment. If it is a cloudy day, you will not see your shadow at all.


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