Many people now know about vitamin D and they know that we can make it from the sun. What most people do not know is that you cannot make vitamin D from just any sunshine. You must have direct enough sun that the UVB's can get through the atmosphere and hit your skin. These UVB's then turn cholesterol (7-dehydrocholesterol) into vitamin D3. Vitamin D3 is then taken to the kidneys where it is made into the active form of vitamin D (25-hydroxyvitamin D).
Know When You Can Make Vitamin D
Where I live in Washington you can make decent amounts of vitamin D from April 5th to September 5th. The trick is to know when you can make higher levels of vitamin D on those days. As an example, the only time you can make significant levels of vitamin D on April 5th is between 11:40am and 12:20pm. This time window keeps expanding until June 21 which is the biggest window (in the US) to make vitamin D. It then starts shrinking again until you cannot make vitamin D anymore. The window where I live gets as big as 9:20am to 3:40pm. This means that you cannot make significant levels of vitamin D where I live after 3:40 pm on any day of the year!!
In northern Washington the window is even smaller and you have to wait till the 9th of April at noon to start making significant levels of Vitamin D. You need to know about which day and what time of day you can make vitamin D. Here are a few general rules I follow to make sure I get vitamin D from the sun anywhere in the US.
1. I do go outside at about noon for 15 minutes (not getting red or burnt).
2. I expose skin to the sun (being modest).
3. I go outside in the spring and summer.
You can only get significant levels of vitamin D in the spring and summer in most places in the US. I do not go out early in the morning or later in the evening to make vitamin D (you will not make very much if any vitamin D). How much vitamin D you make is determined by your latitude, time of year, how much skin you expose to the sun, and how dark your skin is. If you are very light skinned you may be able to make significant levels of vitamin D when others cannot so know your skin. You do not want to burn.
"I have not met anybody yet that seems to have the combination of experience, knowledge, and the practical usage (that Marshall has)*."
" He seems to really know what he is doing. In fact, more than anybody I have met so far."