These four vitamins have what's called a synergistic relationship, meaning they actually help each other work more effectively.
Vitamin D3 helps your body absorb calcium, but without vitamin K2, that calcium can end up in your arteries instead of your bones.
K2 activates special proteins that direct calcium to the right places.
Vitamin A supports immune function while D3 regulates immune responses, and vitamin E protects all these vitamins from breaking down.

Yes, 5,000 IU of vitamin D3 is considered safe for most adults and is within the upper safe limit established by health authorities.

Many people are actually deficient in vitamin D, especially those who don't get much sun exposure or live in northern climates.

If you're taking blood-thinning medications like warfarin (Coumadin), you should definitely consult your doctor before taking Defend because it contains vitamin K2.
While K2 works differently than K1 (which is the main concern with blood thinners), it can still affect clotting.

It depends on how much you're already taking.
Check the labels of your other supplements to avoid getting too much of any single vitamin, especially the fat-soluble ones (A, D, E, K) since they can build up in your body.