A Baltimore reader said she needs extra vitamin D, so her doc prescribed 15 minutes of sunshine daily. Sunlight triggers vitamin D production in the skin. But at low sun angles, the atmosphere filters beneficial UVB rays. She wants to know when the sun is at least 45 degrees above the horizon in Baltimore: "Can you give me any guidance?"
Yes. Our midday solar elevation ranges from 28 degrees in winter to 74 degrees in summer. It exceeds 45 degrees from March 6 to Oct. 6.