There have been several USDA studies published as the National Health and Nutrition Examination Surveys over the pasts 50 years and all of them demonstrate widespread nutritional deficiencies in the US. Our food is calorie dense, but nutritionally deficient in a wide range of vitamins, minerals, and nutrients that include vitamins A, C, and D and minerals such as calcium, iron, and magnesium.
When we migrated from the farm to the city the quality of our food became a problem. We now consume more food products that we do real food. What we're eating is refined, processed, preserved, sprayed with toxic chemicals, and consumed often weeks to months after it is harvested. In addition we don't replenish our soils with the nutrients needed to grow our crops.
Even with supplementation it is difficult to get the nutrition we need to keep our cells healthy. Food is what we need to nourish our bodies, but our food needs to be high quality food that is fresh, unprocessed, unrefined, unpreserved and unsprayed.