Vitamin D is touted as very beneficial and downright necessary for good health. There are studies that demonstrate its benefit to everyone and especially those of us who have multiple sclerosis.
Sunshine is a primary source of vitamin D and requires little to no effort for us to absorb its vitamin D benefits.
However, I seem to be profoundly and negatively impacted simply by being in sunshine, regardless of the temperature. Unfortunately, I haven’t found any research or medical explanation to support this speculation.

Over at least thirty years, there have been more occasions than not when I simply went outside on even a partly cloudy day but in sunlight for less than 3 minutes, only to quickly experience profound fatigue and had to lie down as soon as possible. In fact, I was often wiped-out the rest of the day.
Is it not just the heat but the sun itself?
MS neurologists and other MS medical professionals have simply looked at me quizzically and offered nothing beyond “it must have been the heat.” I doubt it. Some of those days were very cold winter days.
Regardless, there is still more mystery to multiple sclerosis than knowledge.