It’s that time of year when the sun is rising later and setting earlier. And it sits lower in the sky during its daily traverse through the heavens.
Which means the sun is no longer getting high enough in the sky for its ultraviolet-B rays to penetrate the atmosphere and activate vitamin D in your skin.
In fact, if you live in northern latitudes, your skin doesn’t make any vitamin D from November through March—no matter how much sun exposure you get. And by “north” I don’t just mean New England… Any latitude above Atlanta is considered “north” for these purposes.
This is why supplementing with vitamin D at this time of year essential. You should also be increasing your intake of food rich in vitamin D.