The CDC estimated that about 10% of the US population had some form of nutrient deficiency in 2003-2006. There hasn’t been any update since. The most common deficiencies were in vitamin B6, iron, and vitamin D.
Contrast that report with an article from the Linus Pauling Institute, which is part of Oregon State University, that estimates that almost 95% has some form of nutrient deficiency. That’s a big gap from what the CDC reported.
In this case, the CDC has the final say scientifically. They’re the best equipped to measure things at a population-wide scale. However, certain groups of people are at greater risk for nutrient deficiency. Certain races are more likely to lack vitamin D, for example. Women are more likely to lack iron. People who are considered low-income tend to have more nutrient deficiencies.
In other words, there’s not a nutrient deficiency apocalypse. While there are some people with nutrient deficiencies, most have been eliminated by something called fortification. It’s possible to eat foods, such as cereal, and get most of your daily requirements of vitamins and minerals. Food companies fortify their foods with nutrients that people are commonly deficient in. That’s eliminated much of the nutrient deficiencies in the country.
Most people either have adequate nutrition or lack only a few micronutrients in their diet. Some people might need more of a certain nutrient due to health problems or genetic differences. At this point, the scientific community has a general understanding of which populations are likely to be deficient in certain nutrients.
Multivitamins provide a barrage of micronutrients to the body, many of which you flush out through urine. Most research on vitamins shows lackluster results, with a lack of correlation between taking vitamins and preventing disease or early death.
Most likely your vitamins are a waste of money, simply because you’re throwing a bunch of darts at a dartboard to see what sticks. If you think you have a nutrient deficiency, your first step should be to visit a doctor. They can run a blood test to check and suggest ways to replenish whatever micronutrient you’re lacking.
You shouldn’t, however, take a large vitamin pill and hope that it does something. Start with proper nutrition. It’s estimated that between 70-80% of Americans don’t get their daily recommended amounts of fruits and vegetables. Start there, and you might just cure whatever ailment you’re taking vitamins for.