Many people can rattle off the names of the most popular vitamins and the foods that contain them in abundance. But understanding exactly what vitamins are and what roles they play in the body is far more complicated. In fact, though scientists recognize that there are 13 vitamins that are essential for good health, there is no real consensus on what they actually do and exactly how much of them we truly need.

Catherine Price, a science journalist, explores these questions and more in a book that was recently released in paperback, called “Vitamania: How Vitamins Revolutionized the Way We Think About Food.” Ms. Price traces the history of vitamins from their discovery as lifesaving organic compounds that prevented strange diseases to their ubiquity today in foods, beverages and dietary supplements. Ms. Price sheds surprising light on the mythology surrounding vitamins and explains why even basic advice promoted by experts – like the nutrient requirements for healthy adults known as the recommended dietary allowance, or RDA – may be misguided.

Recently, we sat down with Ms. Price to discuss some of the most common misconceptions about vitamins, the reasons vitamin D testing can be misleading, and which questions you should ask yourself before deciding whether to take a multivitamin. Here are edited excerpts from our conversation.

Q. Why did you write this book?

A. I have Type 1 diabetes, which forces me to think about how food interacts with our bodies every time I eat. And yet when my husband turned to me out of the blue one day and asked, “What is a vitamin?” I realized I didn’t know the answer. Vitamins turned out to be a perfect subject for me. I love investigating things that seem so familiar to us that we never think to ask questions about them. They were a mystery hiding in plain sight, and I was intrigued.

Q. How have vitamins changed the way we think about food?

A. Vitamins were the first “superfoods”— they introduced the idea that there are particular foods, ingredients and dietary chemicals that have health benefits that go beyond mere nutrition. It turns out that there’s a direct line between the discovery and early marketing of vitamins and our current beliefs in the magical powers of kale. Learning about the history of vitamins made me much better at recognizing nutritional hype, which helps me make much better — and calmer — decisions about what to eat.

Q. What are some of the most common misperceptions about vitamins?

A. My biggest pet peeve is that when we hear the word “vitamin,” we automatically think of pills instead of food — and then use “vitamin” to refer to all dietary supplements. This is incorrect. There are only 13 vitamins, which are essential for health, compared to over 85,000 dietary supplements for sale in America. Also, we assume that scientists know exactly what vitamins do in our bodies and how much of each we need, but they don’t. We assume that all vitamins and dietary supplements are required to be tested for safety and effectiveness before they’re sold. But they’re not.

Q. Should the average person take a multivitamin?

A. Ask yourself what you eat. Does your plate look like the cover of a Michael Pollan book? Then you’re already getting plenty of vitamins and other nutrients from your food. Do you eat a lot of fortified foods like breakfast cereal and sports drinks? Then you probably don’t need to take a multivitamin either, because you’re essentially eating one. The people who benefit the most from multivitamins are those with restricted diets or health issues that make it hard to absorb nutrients from food, or who get most of their calories from foods that are so junky that they haven’t even been enriched with synthetic vitamins. Man cannot live on potato chips alone.

Q. In your book you say it’s a bad idea to get tested for blood levels of vitamin D and other nutrients. Why?

A. I wouldn’t say it’s necessarily bad — it’s more that it’s not particularly helpful. We know that vitamin D is essential for healthy bones, but the jury’s still out on what else it might do. This makes it impossible to determine what our requirements actually are, which in turn makes it impossible to figure out what an optimal level should be. And despite an ongoing standardization effort, results for the same blood sample can differ depending on which lab they’re sent to. It’s like taking an exam that doesn’t have an answer key — and that’s scored differently depending on who grades it.

Q. Why is taking large doses of some vitamins a bad idea?

A. It’s a bad idea to assume that just because something is essential in small doses, bigger doses must be better. Some vitamins are known to be toxic in high doses. Vitamin A is the most notorious. In some cases, high doses of vitamins that we thought would be helpful have been shown to cause more harm than good. In the 1990s, high doses of beta-carotene, which is a precursor to vitamin A, were tested as a possible prevention for cancer, but were eventually linked to an increased risk for lung cancer, especially among smokers. Remember: Even water can kill you if you drink too much of it.

Q. In your book you argue that the “Percent Daily Value” figures on food and supplement labels are close to meaningless. Why?

A. First of all, we each have different vitamin requirements, which means that 100 percent for me is not 100 percent for you. Second, the recommended dietary allowances aren’t meant as personalized recommendations to begin with. And third, most of the percentages in the “percent daily value” column on current food and supplement labels are calculated off of the RDAs from 1968. Yes, 1968. The FDA plans to use more updated recommendations in the next version of the nutrition and supplement facts panels, but for now, most of those numbers are still based on recommendations that are nearly a half a century old.

Q. What are some of the most peculiar things you learned about vitamins while writing this book?

A. That synthetic vitamin D is made by irradiating grease from sheep’s wool. That American politicians became convinced that thiamin deficiencies would make us lose World War II. That the guy who discovered vitamin B12 did so by eating raw meat, regurgitating it, and then tube-feeding it to his unknowing patients. And that before being affiliated with vitamins, Fred Flintstone and Barney Rubble used to advertise Winston cigarettes. It turns out that the story of vitamins is much bigger, weirder, more interesting and more useful than I ever could have anticipated.