Because going outside is NOT enough unless you work outside all day. And winter season comes up ... many especially in the NE lose Vitamin D.

If you want to KEEP out of a hospital You need to take Vitamin D daily. One of the doctors (cant remember which one) said in a video that you need to have your blood Vitamin D hydroxy level at or above 50 ng/mL.

So when you get a blood test check your Vitamin D-Hydroxy level.

Normal is considered 30.0 up to 100.0