The three things in which most Americans have deficiencies are probably Vitamin D3, Magnesium and Zinc. After I began D3 supplementation 20 years ago, my constant round of Wintertime head and chest colds ceased. When I told my Cardiologist that I hadalso begun taking Magnesium and Zinc and a popular enzyme known as Co-Q-10, he said, "Good! I take them, too!"Magnesium and Zinc are available in many different chemical compounds, some of which are virtually worthless because of low bio-uptake. You can find out all the ins-and-outs of the different formulations from the doctors on YouTube. After experimenting, I settled on Magnesium Glycinate and Zinc Gluconate, both of which I get from Brother Amazon Prime.