How are Vitamins and Nutrients Absorbed in the Body?
It’s a common misnomer that food is just fuel – that everything we consume is digested and transformed into energy. And though that may be the case for much of what we eat, there are many things inside our food we don’t use for fuel. And in a lot of ways, they’re just as if not more important. In reality, without these other minuscule components, we may not even be able to process that food.
These microscopic compounds are small, yet mighty. Necessary for life, they’re known as essential nutrients – though you may be more familiar with them as vitamins or minerals.
Because our bodies cannot create them, they require regular ingestion of them.
And without them, we would cease to exist.
What Makes Vitamins and Minerals So Important?
You have your macro-nutrients (fats, proteins, and carbohydrates) and then you have your micro-nutrients. The first micronutrient was discovered in 1912 by Polish-born biochemist Casimir Funk. He began hypothesizing that there must be other ‘essential nutrients’ in our food required for optimal health. He termed these mysterious compounds as “vital amines,” eventually shortened to what we know them as, vitamins.
Over a hundred years – and an exceptional amount of research – later, scientists have created a list of almost 30 vitamins and minerals necessary for normal function. If even just one of these micronutrients is deficient in your diet, the consequences can be extreme. For every vitamin or mineral deficiency, your body can begin to experience unique, serious, and rapid dysfunctional effects.
For example, vitamin A deficiency can cause blindness because it is responsible for the production of the pigments in the retina of the eye.1 Necessary to form healthy teeth, skeletal and soft tissue, mucus membranes, and skin, vitamin A deficiency is also closely associated with severe, sometimes fatal infections.
Deficiencies in minerals also can have disastrous side effects. You may be familiar with anemia associated with low levels of iron.2 Iron is a necessary component of red blood cells and helps store and transport oxygen to your tissues. If your iron levels are low, you may experience extreme bouts of fatigue and shortness of breath due to low oxygen distribution. Long term, it can develop into rapid or irregular heartbeats and place considerable strain on your heart to compensate for the lack of oxygen in your tissues.
Each micronutrient has a role and a part to play inside your body. Conversely, each deficiency is closely associated with a serious disease or condition. Thus – getting enough essential micronutrients in your diet is the ultimate necessity to high-functioning, optimal health.
It’s Not Just What You Eat, It’s Also What You Absorb
In Western civilization, having access to nutrient-dense foods is rarely a concern. Modern Nutrition advocates for ‘eating the rainbow’ or consuming all colors of fruits and vegetables to ensure you’re taking in all the vitamins and minerals you need.
And fortunately, modern society has also taken note of history and added extra nutrients to many foods commonly found in the marketplace. Consider enriched grains and flour – most of the cereals, bread, and other processed grains you may eat have been fortified with various B vitamins (and other minerals) to promote a more stable nutritional diet. These days, if you’re incorporating a fair mixture of whole foods - like fruits, vegetables, grains, and protein sources - in your diet, you’re most likely ingesting most of your essential nutrient needs.
But sometimes the issue isn’t always what you eat, but the ability of your body to absorb it.
Depending on the current state of your body, your digestive system may not be properly prepared for its role in the absorption process. In order to properly take in nutrients, your system must be primed and ready to go. This requires a couple of factors, such as a healthy intestinal lining and a balanced gut microbiome. But it also depends on how and where your micronutrients are absorbed – which brings us to the next thing: where are nutrients absorbed? And how can I support or improve nutrient absorption?
Nutrient Absorption and the Digestive System
The first role of your digestive system is to take the foods you consume and begin breaking them down into smaller, more usable components.3 This first wave begins immediately upon placing food in your mouth. As your teeth grind up the food into smaller bits, your salivary glands begin secreting enzymes with the sole purpose of breaking down carbohydrates. Simultaneously, your oral microbiome gets to work, using various bacteria in your mouth to further break down nutrients that can aid in regulating blood pressure and protecting against pathogens. Once swallowed, this compacted food enters the esophagus and travels to the stomach, where it is exposed to a highly acidic solution that further degrades carbohydrates, proteins, and fats.
As your stomach degrades the major macronutrients in your diet, it mixes it all together with the natural rhythms of its peristaltic motion. Then, the digested food is released into the small intestine where even more digestive enzymes are secreted by the liver, gallbladder, and pancreas4 as it prepares for its role in nutrient absorption.
The Small Intestine
The small intestine is made up of three different sections: the duodenum, the jejunum, and the ileum. The majority of the nutrient absorption process occurs in these sections of the small intestine before finally passing the remaining components of your food into the large intestine for final touches. Your small intestine absorbs the broken-down components of your food now in the form of simple sugars, amino acids, fatty acids – not-to-mention the micronutrients in your diet.
Most of the vitamins and minerals you consume are also absorbed in the small intestine, but each one requires its own unique mechanism to cross the intestinal cell lining.
Understanding the differences between types of micronutrients is one way you can personally improve your absorption process. For example, there are two categories of vitamins: water-soluble (all the various Bs and C) and fat-soluble (like A, D, E, and K). Water-soluble vitamins require water for transport. Getting plenty of fluids can improve your body’s ability to absorb and transport these nutrients through diffusion. Conversely, fat-soluble vitamins – you may have guessed – require fat to aid in their absorption. One of the best ways to help improve their transport is to consume healthy fats with fat-soluble vitamin rich foods to ensure your body can properly absorb them.
Moreover, both water-soluble vitamins and minerals also require specialized ‘transporters’ found in the lining of intestinal cells to cross the cell membranes and make their way into the blood. These nutrient transporters make sure the appropriate particles pass into the cell. The more specialized the function, the more protective. This complex and particular process of absorption ensures that only exactly the right components enter the bloodstream: nothing more, nothing less.
As the digested food passes through the small intestine and undergoes the absorption process, it finally transitions into the large intestine where it faces the final stretch before excretion.
The Large Intestine
Historically, scientists have considered the role of the large intestine to be fairly straightforward in digestion. As the remaining components of food material enter the large intestine, it primarily functions to remove any excess water and salts to prepare for excretion. As this material enters it, the majority of nutrients have already been digested and absorbed. What remains is typically reduced to harder to digest remnants, such as non-digestible fibers and whatnot.
Now we know this area is rich in other key functions. With our broader understanding of the gut microbiome, we understand that the majority of gut bacteria colonize this region – taking in what our body cannot digest and breaking it down to their – and often our – benefit.
Although bacteria thrive in all areas of our digestive system – including the small intestine – it’s the ecosystem within the colon that upholds a lot of our intestinal integrity. Here, they transform many leftover food remnants into additional sources of many essential nutrients beneficial to our body.
Bacteria: The Understated Heroes of Vitamin & Nutrient Absorption
Though we don’t necessarily require microbes for nutrient absorption, they serve many supporting functions that don’t just facilitate the process but can even increase the levels of essential nutrients.
As you may know, a healthy gut ecosystem works to uphold the integrity of the intestinal lining. To truly optimize the process of absorption, the body requires healthy intestinal cells for nutrient uptake. It is well established that imbalance inside your gut ecosystem can cause intestinal cells to decay and die, disrupting nutrient uptake.5 This greatly reduces the capacity of our digestive system to absorb essential nutrients required to repair and maintain healthy cells.
Our gut bacteria have also been shown to contribute to the amount of many essential nutrients. Just one example is vitamin K. Though found in our diet, upwards of half of our daily vitamin K requirement is actually made by bacteria in our gut.6 If your gut ecosystem is imbalanced, your body may be experiencing a shortage of colonies that contribute to our vitamin levels necessary to combat various deficiencies.
When it comes to understanding digestion and your vitamin and mineral needs, every person is unique. Ultimately, it comes down to how your body functions, your own personal needs based on lifestyle, diet, and goals, and the health of your body and your various microbiomes. Learning where the gaps in your diet may be is just the first step toward better nutrient absorption.
1 Sommer A. (2008). Journal of Nutrients. 138(10):1835-9. doi:10.1093/jn/138.10.1835.
2 Jimenez K, Kulnigg-Dabsch S, Gasche C. (2015). Gastroenterol Hepatol (N Y). 11(4):241-50.
3 Boland M. (2016). J Sci Food Agric. 96(7):2275-83. doi: 10.1002/jsfa.7601.
4 Ogobuiro I, Gonzales J, Shumway KR, et al. (Updated 2023 Apr 8). Physiology, Gastrointestinal. In: StatPearls [Internet].
5 Krajmalnik-Brown R, Ilhan ZE, Kang DW, DiBaise JK. (2012). Nutr Clin Pract. ;27(2):201-14. doi: 10.1177/0884533611436116.
6 Conly JM, Stein K. (1992). Prog Food Nutr Sci. 16(4):307-43.