I don't think many people appreciate that we only get 10% of our vitamin D from food and 90% from the sun. Also that very little of our skin is exposed to the sun these days and as we get older we lose the ability to turn that limited exposure into vitamin D. The average 70 year old can only convert 25% of what they could when they were 20 so it's no wonder most of us are deficient and need D3 as we get older.
It's also linked to dementia with D3 and zinc suggested to help fight/slow vascular dementia which are also vital for our immune response.
