Depends. Sunlight just converts a precursor molecule (7-dehydrocholesterol) to D3. The precursor is a product of the cholesterol synthesis system. I personally

Depends. Sunlight just converts a precursor molecule (7-dehydrocholesterol) to D3. The precursor is a product of the cholesterol synthesis system. I personally believe you don't need any exposure to direct sunlight to get required D3 as long as you eat food natural to humans, specially if the diet is close to that of indigenous groups living in similar environment for thousands of years. We store D3 in our fat and you can also get it when you eat animal fat. However, if you really want to use sun exposure, I recommend an app called dminder which tells you, based on your location, if and when sun exposure will give you Vitamin-D.