Hi doc , what will be the best vitamins supplements for my husbnd 40 and physically active as mechnical engr, his immune system is getting low recntly?

Instead: Remember there is no one size fits all for supplementation, but in general, unless you have to, consider opting for optimizing your husband's overall health. This means making sure he is minimizing stress, remaining active, sleeping well, eating well(focus on whole foods with lots of color, minimal processing and lots of veggies) and remaining socially active.