Lots of lab tests show people to be low in this vitamin or that mineral. However, food science has proven that just adding a missing nutrient is not an efficient way to build up those levels. Nutrients (vitamins, minerals, trace elements, etc.) do not function well in isolation, so taking a bottle of this or a swallow of that is expensive and with negligible results. Every element needs a whole host of "partners" for absorption and effective utilization. Any other approach is just a waste of money and can, in fact, cause more problems. Most good doctors will admit that they had no nutritional training in medical school so I'd be wary of anyone who doesn't.
No matter what a person is low in, the best way to counteract it is with a comprehensive (70+ ingredients in proper proportion) in a highly absorbable form. You want bioavailability (absorption, surviving the digestive process, easy uptake), synergism (proper blend), optimal nutrient levels (absolutely NOT the old RDIs which are usually bare minimums), and guaranteed quality ingredients (no warning labels, analysis for purity, patents, and approved for sale in countries with very strict regulatory agencies (for more than the US).
The key is cellular nutrition - getting the nutrients into the individual cells where the real work of the body occurs. What you swallow is immaterial - what you absorb is key.