Nothing in the subject of nutrition is as mystical as the vitamins. Are they magic substances to prolong life? Do they provide the difference between health and disease? Are they overrated and overhyped? So many words grace the net on the benefits or lack thereof on vitamins and health. Despite my background in food science, I have become confused. I was searching for answers. As a scientist, I shy away from proclaiming truth on any topic. Studying a topic brings us closer to the truth, but we never reach absolute truth. In my quest for clarification I formulated eight questions to help my understanding. I started out with an elementary set, and proceeded to greater complexity.
To find answers I sought out the latest edition of a prominent textbook in the field. I chose The Vitamins: Fundamental Aspects in Nutrition and Health by Combs and McClung. It was a magic carpet ride though in-depth technical language. I travelled back to the wonderland of food biochemistry. It was an incredible journey. Each week this month I will explore the answers I found in the book to two of these questions. Some answers were clear and detailed. Others not so much. For each question I provide an answer based on my understanding of what I read. I use one vitamin as an example to further illustrate that message.
Let’s start with the first two sets of questions:
1. What is a vitamin? How were they discovered? How to they contribute to our health? Elementary, yes. Simple, not so much. Vitamins are “essential to life.” They do not “serve structural functions” or “provide significant energy” like “other nutrients.” We only need small amounts of them to maintain health. But consuming less than what we need over time can lead to severe health consequences. Vitamins don’t share “close chemical or functional characteristics.” The authors do not offer a simple definition of a vitamin. They offer a set of five bullet points of qualifying criteria. Vitamins are (i) organic chemicals, (ii) essential to metabolism, and (iii) found in a whole foods. They prevent (iv) a specific deficiency disease and (v) are not synthesized in the body. If that is not confusing enough, some vitamins exhibit exceptions to these rules. Then some compounds sort of fit these rules but are not considered vitamins. Go figure!
Each vitamin has its nutrient-reveal story. Most discoveries relate to a search for a cure to a specific deficiency disease. Some scientists noted that certain populations were susceptible to a disease. Others in the same location were not. Discovery of thiamin is the most well-known tale. The discovery of riboflavin was of particular significance. “[I]t bridged the gap between an essential component and cell enzymes and cellular metabolism,” noted Paul György. Biotin and vitamin B6 were also discovered by György. It took a bushel of corn to find biotin and four tons of spinach to isolate folate. Vitamin research turned nutrition into a science.
How vitamins contribute to health is not as simple as it seems. The easiest answer is that they keep us physiologically fit. Each vitamin performs one or more functions in daily metabolism. But it is more complicated than that! Physiological fitness depends on the interaction of vitamins in the body. Proper levels of other vitamins enhance the function of a specific vitamin. Lower levels of certain vitamins impair a specific vitamin’s performance. Too much of some vitamins interfere with the proper function of other vitamins. Think of cellular metabolism as a concert with each vitamin as a critical instrument. Alas, such a beautiful analogy oversimplifies the role of vitamins in our physiology.
Riboflavin represents a typical vitamin. It is a water-soluble organic compound known also as vitamin B2. We find riboflavin in its natural state in meat, milk, and eggs. Wheat bran, oats, and spinach are good plant-based sources of riboflavin. Anyone who has ever memorized the Krebs Cycle remembers FAD, FMN, and FADH2. Riboflavin derivatives are essential cofactors of enzymes in the cycle. Without it, metabolism doesn’t function properly. And yet, there is no specific deficiency disease associated with riboflavin.
Subclinical deficiencies can occur. Over 25% of poor, urban youth in the USA live with insufficient levels of riboflavin in their bodies. Although humans cannot synthesize the vitamin, microbes in the hindgut can produce riboflavin. Light and radiation destroy this vitamin. It also leaches out into cooking water or exudes in meat drippings. Parboiling of rice protects riboflavin from loss. The vitamin is stable to heat during cooking and processing.
- Are synthetic vitamins less nutritious than natural vitamins? Another simple but controversial question. Another not so simple answer. Combs and McClung use the terms biopotency and bioavailability. First, most vitamins are not single chemical compounds. Different chemical forms of a vitamin are vitamers. Some vitamers are more stable in foods than others. Internal conditions in the food affect the amount and type of vitamer present. External conditions during processing or storage can protect or degrade vitamin potency.
I learned this lesson during my first study as an Assistant Professor at the University of Georgia (1). We monitored loss of quality of fresh broccoli during refrigerated storage. Vitamin C, ascorbic acid, concentration is a freshness index for most fresh foods. Vitamin C disappears during refrigerated storage of fresh vegetables. Ascorbic acid levels in stored broccoli did not budge. A trip to the library in those pre-internet days revealed that Vitamin C is stable in fresh broccoli. I never learned why, but the cellular matrix may have protected ascorbic acid in broccoli.
The matrix protects, but it can also limit absorption of a vitamin during digestion. Compounds in the gut are not in the body until they cross the intestinal mucosa. Vitamins not absorbed across that barrier don’t nourish our bodies. With any specific vitamer, absorption is not an all-or-nothing event. Rather probability governs the level of absorption. Once a vitamin makes its cellular destination its metabolic value relates to vitamer biopotency.
Back to the question comparing natural and synthetic vitamins. I read no direct comparison between the two types. My answer then must be by inference. Almost all mention of sources for specific vitamins were natural foods. In certain cases, processed foods appeared as sources. Heating in the kitchen or processing plant reduces vitamin levels as much as 50% or more. The remaining levels are stable. Refrigerated storage also results in major losses of vitamins in fresh foods. Medical treatment of humans with insufficient vitamin levels is through careful administration of synthetic vitamins. I conclude that biopotency of any vitamin relates to the amount present and the form of the vitamer.
Vitamin effectiveness depends on absorption in the gut and biopotency at its destination. Values appearing on nutritional labels of processed foods take these factors into account. Natural vitamins in whole foods vary by variety, growing conditions, or refrigeration.
Niacin is a vitamin consumed in both natural and synthetic forms. It is highest in brewer’s and baker’s yeast as well as wheat bran and germ. Milk, meat, and fish are also good sources. In some plant tissue, niacin is bound in complexes not broken down in the gut. The American South suffered a scourge of pellagra during the Great Depression. The cause was a reliance on cornbread in the diets of poor Southerners. Although corn is loaded with niacin, the vitamin was not available to humans. Fortification of cereals in the USA alleviated the niacin problem. In Central American soaking and cooking corn in lime releases niacin for absorption. In the Krebs Cycle we note this as NAD(H) or NADP(H). Other vitamers of niacin include nicotinic acid, nicotinamide, nicotinic acid mononucleotide, and nicotinamide riboside. Forms of niacin are stable to heat as well as during refrigerated storage of fresh foods.
Large doses of niacin are preventive medications for heart disease. My physician prescribed niacin to lower my blood lipids. They came as a coral-colored horse tablet which I took each evening before bedtime. The downside is that flushing accompanied by an itchy rash occurs within two hours after swallowing. In The End of Craving, Mark Shatzker noted that farmers use B vitamins such as niacin to fatten up livestock. The author suggests that vitamin fortification leads to high levels of American obesity. The Vitamins mentions the role of added B vitamins in weight gain of farm animals. It does not suggest that fortification of grain products affects weight-gain in humans.
Take-home lesson. First, it is important to understand that I asked the questions before I opened the book to read it. I have my own thoughts (or biases) about vitamins. I did not want to prejudge my blog by forming questions after the fact to verify my thoughts. I found that my perspective going into my quest was either mistaken or outdated in some cases. I also found that my terminology needed refreshing. Adopting a new terminology, led to a new appreciation of specific vitamins. It also gave me a new perspective on nutrients in general. I tried to not let confirmation bias color my perspective or answers. I found the experience to be refreshing and informative.
Vitamins are much more complex than my original conception. There are set criteria a compound or family of compounds must meet to qualify as a vitamin. Not all so-called vitamins qualify on all counts. Other compounds meet these qualifications only to achieve status as quasi-vitamins. Much of my instruction in vitamins or reading about them started with “assume a vitamin.” What a concept! My nutrition education taught me that the role of a vitamin was specific prevention of deficiency diseases. Well, it isn’t that simple. There are two main stages of insufficiency between sufficiency and deficiency. More on that topic next week. I also learned about biopotency and all the factors that affect vitamin effectiveness.
Handling and processing of foods affects loss of vitamins in foods. The effects are greater on the stability of riboflavin than niacin. The greatest concern about niacin is its bioavailability. It must be in a form that can release in the gut for absorption across the intestinal mucosa. Natural or synthetic is not the right question. The important characteristics of a vitamer are its stability, bioavailability, and its biopotency.
Next Week: How much of a vitamin do we really need?
(1) Shewfelt, R.L., K.M. Batal, and E.K. Heaton, 1983. Broccoli storage: effect of N6-benzladenine, packaging, and icing on color of fresh broccoli. Journal of Food Science 48:1594-1597.