My body stopped making Vitamin D on its own. Taking D3/K supplements was a life saver and for seasonal affective disorder. And now I seem to be back to typical levels with just sun exposure.
Not who you are asking, but most folks find out with blood tests. It is also pretty common for folks to produce less as they age, and it isn't a small difference.
Are you going out in the morning? That's when your get vitamin D, almost nothing in the afternoon.
This just isn't true. How much you get is going to depend on the angle and strength of the sunlight, the amount you get, the amount of skin exposed, and the color of your skin. (dark skin produces less than light skin, and makes it difficult to produce enough the further north/south you are).