If you hear this word, the instant thought might be you walking around the grocery stores and skimming through the aisles full of all sorts of vitamin supplements. If you go closer to the aisle, you notice that the supplements have different sizes of containers, different alphabet letters and numbers, and different units for each vitamin. It can be confusing when it comes to purchasing vitamin supplements due to this broad range of options. However, people tend to overlook the general fact that vitamins are also abundant in various foods, and they can get enough vitamins by having a variety of nutritionally balanced meals with plenty of fruits and vegetables.

Vitamins are different from macronutrients like carbohydrates, protein, and fat in many important ways. While the human body needs large amounts of the macronutrients to use as main energy sources, only small amounts of micronutrients are required. For example, vitamins may be in a dose as small as a mere microgram. Unlike carbohydrates, protein, and fat; vitamins are not a source of energy, which explains why such a small amount is necessary. Vitamins are organic compounds like carbohydrate, protein, and fat, and they are also as essential as macronutrients for normal functioning, growth, and maintenance of the body. For example, as an overview, vitamin E and C act as antioxidants, B vitamins act as coenzymes in energy-producing metabolic reactions, vitamin D and K are essential for bone health, vitamin A plays an important role in vision, and vitamin K contributes to blood clotting. Having an awareness of how crucial vitamins are for the human body to stay healthy, can prevent deficiency and avoid serious health problems.

Vitamins can be largely classified into 2 types; water-soluble and fat-soluble. Vitamin A, D, E, and K are soluble in fat due to their lipid-like structures, whereas B vitamins and vitamin C are soluble in water. Water-soluble vitamins are absorbed in the intestine and delivered directly to the bloodstream, while fat-soluble vitamins are absorbed ‘with fat’ and transported via lymph to the bloodstream and eventually to the liver. These different methods of vitamin transport and absorption affect how vitamins are stored and how much of a vitamin can be tolerated by the human body.

Water-soluble vitamins like B vitamins and vitamin C are readily absorbed into the body and excess amounts of water-soluble vitamins are excreted in the urine. Toxicity of water-soluble vitamins is generally rare since extra water-soluble vitamins are excreted rather than being stored. However, consuming large amounts of certain vitamins such as vitamin B6, folate, niacin, and even vitamin C can be harmful; this is likely caused by taking unnecessarily high doses of vitamin, rather than having excessive food sources of those vitamins. Fat-soluble vitamins are stored in the liver and fatty tissues of the body and they are excreted much more slowly than water-soluble vitamins. Therefore, having excessive amounts of fat-soluble vitamins can pose a greater risk of toxicity than water-soluble vitamins. Again, it is less likely to reach toxic levels of fat-soluble vitamin by consuming excess food sources; it is riskier when taking a high dose of fat-soluble vitamin supplements without any consultation from health professionals. When counseling clients, I find this especially true with Vitamin D. If you are supplementing have your doctor check your Vitamin D level and prescribe an appropriate dose if needed. Toxic levels of vitamins can result in negative side effects causing health problems.

Understanding the units of measure on the containers of vitamin supplements can be overwhelming. When it comes to macronutrients like carbohydrates, proteins, and fats, all people need to know is how many ‘grams’ they should have for each macronutrient. However, when it comes to vitamins, there are various units for each vitamin, and along with the units, the amounts vary. This is because only small amounts of vitamins are required for individuals and therefore units like grams are not applicable. The most common units for vitamins are mg (milligram), mcg (microgram) or ug, and IU (international unit). International unit (IU) is an internationally accepted amount of a substance. The size of an international unit (IU) varies depending on the vitamin or drug it is used to measure.

Overall, we know vitamins are important and vitamin intake should be monitored to stay healthy. During the healthcare pandemic, even more so we recognize the importance of vitamin intake to strengthen the immune system and, hopefully, avoid getting sick. This also has brought attention to the importance of having nutritious meals that contain adequate amounts of vitamins and other pertinent nutrients to prevent disease by making our bodies strong. Vitamins should come first from natural or fortified food choices. A health professional may recommend vitamin supplements for people with certain conditions, during pregnancy, or for those with a restrictive diet.

Nicole Maslar RDN, LDN

*Researched and written in conjunction with UMASS Nutrition & Dietetic student Nina Seok


Insel.P., Ross. D., McMahon.K., and Berstein.M. Nutrition 6th edition, Johns & Barlett Learning(2017)

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