No obvious link between the two.
Is your kidney function normal ?
Are your platelet levels normal?
Any cause identified for the low Vit D levels?
If your levels do not increase this would raise the possibility that you are having a problem absorbing vitamin D from your gut.
I will post you a link about "malabsorption" as this condition is called.
In relation to your potassium level can I ask if you are on any medication and if the potassium level has been raised consistently?
Apologies for that.
Worth finding an alternative to the atenolol - this can cause a raised potassium level.
"beta blockade" on the link below