I saw a TV program recently where the people who took an hours extra outside in the sunlight each day improved their vitamin D levels as well as those given the tablets.
For me living is the gloomy north east US, even a couple of hours extra exposure never bumps my level up to 20.
Not so much money to be made out of advising people to get more sunlight though.
Yeah but the dermatologist is making good $$$$$$ freezing the precancerous lesions off me caused by the sun exposure.
Vitamin D3 supplements are incredibly cheap at only pennies per day over the counter with no prescription. My Dr. isn’t making a thing on me for those.
Hugh
North of ~40 degrees latitude, our skin generally can’t manufacture vitamin D from sunlight in the winter (~Nov-~March). The sun is too low in the sky, and the UVb rays are filtered by the atmosphere (UVb makes the vitamin D, UVa doesn’t). So while being in the sun in December might give us a psychological boost, it doesn’t boost our vitamin D levels.
There’s also some evidence that the cancer risk comes when exposed just to the UVa, with the UVb filtered out. In other words, being behind glass, winter sun exposure, and sunscreens all filter UVb but not UVa.