I know from my time in my 30's messing around with testogel, it does wonders for the brain and talking to someone from South Africa who worked in the medical field, they use testosterone therapy for treating dementia.

Coupled with factors like calcium, iron, fibre, phytates and tannins inhibit zinc, and zinc is required for so much in the body, I'm of the opinion we dont get enough zinc.

Zinc and aspartate mediate cysteine immune responses. So much needs zinc, the active form of Vit D3 needs zinc to protect the bones, but supplement form of D3 doesnt, but the supplement form of D3 needs to activated by the kidneys. D3 needs a zinc finger (zinc & cysteine).

Zinc plays such a major part in biology, I'm surprised the RDA is set so low, but also not surprised when looking at the method for calculating these RDA's, which involved healthy young adults, and not old people!